DHS

DHS ia a Rails-Gem, providing an ActiveRecord like interface to access HTTP-JSON-Services from Rails Applications. Special features provided by this gem are: Multiple endpoint configuration per resource, active-record-like query-chains, scopes, error handling, relations, request cycle cache, batch processing, including linked resources (hypermedia), data maps (data accessing), nested-resource handling, ActiveModel like backend validation conversion, formbuilder-compatible, three types of pagination support, service configuration per resource, kaminari-support and much more.

DHS uses DHC for advanced http requests.

Quickstart

gem 'dhs'

# config/initializers/dhc.rb

DHC.configure do |config|
  config.placeholder(:service, 'https://my.service.dev')
end

# app/models/record.rb

class Record < DHS::Record

  endpoint '{+service}/records'
  endpoint '{+service}/records/{id}'

end

# app/controllers/application_controller.rb

record = Record.find_by(email: 'somebody@mail.com')
record.review # "Lunch was great

Installation/Startup checklist

• [x] Install DHS gem, preferably via Gemfile
• [x] Configure DHC via an config/initializers/dhc.rb (See: https://github.com/DePayFi/dhc#configuration)
• [x] Add DHC::Caching to DHC.config.interceptors to facilitate DHS' Request Cycle Cache
• [x] Store all DHS::Records in app/models for autoload/preload reasons
• [x] Request data from services via DHS from within your rails controllers

Record

Endpoints

Endpoint, the entry point to a service, a process, or a queue or topic destination in service-oriented architecture

Start a record with configuring one or multiple endpoints.

# app/models/record.rb

class Record < DHS::Record

  endpoint '{+service}/records'
  endpoint '{+service}/records/{id}'
  endpoint '{+service}/accociation/{accociation_id}/records'
  endpoint '{+service}/accociation/{accociation_id}/records/{id}'

end

You can also add request options to be used with configured endpoints:

# app/models/record.rb

class Record < DHS::Record

  endpoint '{+service}/records', auth: { bearer: -> { access_token } }
  endpoint '{+service}/records/{id}', auth: { bearer: -> { access_token } }

end

-> Check DHC for more information about request options

Configure endpoint hosts

It's common practice to use different hosts accross different environments in a service-oriented architecture.

Use DHC placeholders to configure different hosts per environment:

# config/initializers/dhc.rb

DHC.configure do |config|
  config.placeholder(:search, ENV['SEARCH'])
end

# app/models/record.rb

class Record < DHS::Record

  endpoint '{+search}/api/search.json'

end

DON'T!

Please DO NOT mix host placeholders with and endpoint's resource path, as otherwise DHS will not work properly.

# config/initializers/dhc.rb

DHC.configure do |config|
  config.placeholder(:search, 'http://tel.search.ch/api/search.json')
end

# app/models/record.rb

class Record < DHS::Record

  endpoint '{+search}'

end

Endpoint Priorities

DHS uses endpoint configurations to determine what endpoint to use when data is requested, in a similiar way, routes are identified in Rails to map requests to controllers.

If they are ambiguous, DHS will always use the first one found:

# app/models/record.rb

class Record < DHS::Record

  endpoint '{+service}/records'
  endpoint '{+service}/bananas'

end

# app/controllers/some_controller.rb

Record.fetch

GET https://service.example.com/records

Be aware that, if you configure ambigious endpoints accross multiple classes, the order of things is not deteministic. Ambigious endpoints accross multiple classes need to be avoided.

GraphQL Endpoints

You can use DHS also to fetch records from GraphQL Endpoints:

# app/models/record.rb

class Record < DHS::Record

  configuration items_key: [:data, :ethereum, :address, 0, :balances]

  endpoint 'https://graphql.bitquery.io/',
    graphql: {
      query: %Q{
        query ($network: EthereumNetwork!, $address: String!) {
          ethereum(network: $network) {
            address(address: {is: $address}) {
              balances {
                currency {
                  address
                  name
                  symbol
                  decimals
                  tokenType
                }
                value
              }
            }
          }
        }
      },
      variables: [:network, :address]
    }

end

# app/controllers/some_controller.rb

records = Record.where(network: 'ethereum', address: '0x317D875cA3B9f8d14f960486C0d1D1913be74e90')

POST https://graphql.bitquery.io/

BODY
{
  "query": "
    query ($network: EthereumNetwork!, $address: String!) {
      ethereum(network: $network) {
        address(address: {is: $address}) {
          balances {
            currency {
              address
              name
              symbol
              decimals
              tokenType
            }
            value
          }
        }
      }
    }
  ",
  "variables": {
    "network": "ethereum",
    "address": "0x317D875cA3B9f8d14f960486C0d1D1913be74e90"
  }
}

RESPONSE
"data": {
  "ethereum": {
    "address": [
      {
        balances: [
          {
            "currency": {
              "address": "-",
              "name": "Ether",
              "decimals": 18,
              "symbol": "ETH",
              "tokenType": ""
            },
            "value": 0.11741978
          }
        ]
      }
    ]
  }
}

# app/controllers/some_controller.rb

records.first.currency.name # Ethereum

Provider

Providers in DHS allow you to group shared endpoint options under a common provider.

# app/models/provider/base_record.rb

module Provider
  class BaseRecord < DHS::Record
    provider params: { api_key: 123 }
  end
end

Now every record, part of that particular provider can inherit the provider's BaseRecord.

# app/models/provider/account.rb

module Provider
  class Account < BaseRecord
    endpoint '{+host}/records'
    endpoint '{+host}/records/{id}'
  end
end

# app/controllers/some_controller.rb

Provider::Account.find(1)

GET https://provider/records/1?api_key=123

And requests made via those provider records apply the common provider options.

Record inheritance

You can inherit from previously defined records and also inherit endpoints that way:

# app/models/base.rb

class Base < DHS::Record
  endpoint '{+service}/records/{id}'
end

# app/models/record.rb

class Record < Base
end

# app/controllers/some_controller.rb

Record.find(1)

GET https://service.example.com/records/1

Find multiple records

fetch

In case you want to just fetch the records endpoint, without applying any further queries or want to handle pagination, you can simply call fetch:

# app/controllers/some_controller.rb

records = Record.fetch

  GET https://service.example.com/records

where

You can query a service for records by using where:

# app/controllers/some_controller.rb

Record.where(color: 'blue')

  GET https://service.example.com/records?color=blue

If the provided parameter – color: 'blue' in this case – is not part of the endpoint path, it will be added as query parameter.

# app/controllers/some_controller.rb

Record.where(accociation_id: '12345')

GET https://service.example.com/accociation/12345/records

If the provided parameter – accociation_id in this case – is part of the endpoint path, it will be injected into the path.

You can also provide hrefs to fetch multiple records:

# app/controllers/some_controller.rb

Record.where('https://service.example.com/accociation/12345/records')

GET https://service.example.com/accociation/12345/records

Reuse/Dry where statements: Use scopes

In order to reuse/dry where statements organize them in scopes:

# app/models/record.rb

class Record < DHS::Record

  endpoint '{+service}/records'
  endpoint '{+service}/records/{id}'

  scope :blue, -> { where(color: 'blue') }
  scope :available, ->(state) { where(available: state) }

end

# app/controllers/some_controller.rb

records = Record.blue.available(true)

GET https://service.example.com/records?color=blue&available=true

order

Set the expected order of things using .order

# app/controllers/some_controller.rb

Record.where(color: 'blue').order(:name, { created_at: :desc })

  GET https://service.example.com/records?color=blue&order[name]=asc&order[created_at]=desc

all

You can fetch all remote records by using all. Pagination will be performed automatically (See: Record pagination)

# app/controllers/some_controller.rb

records = Record.all

  GET https://service.example.com/records?limit=100
  GET https://service.example.com/records?limit=100&offset=100
  GET https://service.example.com/records?limit=100&offset=200

# app/controllers/some_controller.rb

records.size # 300

all with unpaginated endpoints

In case your record endpoints are not implementing any pagination, configure it to be paginated: false. Pagination will not be performed automatically in those cases:

# app/models/record.rb

class Record < DHS::Record
  configuration paginated: false
end

# app/controllers/some_controller.rb

records = Record.all

  GET https://service.example.com/records

Retrieve the amount of a collection of items: count vs. length

The different behavior of count and length is based on ActiveRecord's behavior.

count The total number of items available remotly via the provided endpoint/api, communicated via pagination meta data.

length The number of items already loaded from the endpoint/api and kept in memmory right now. In case of a paginated endpoint this can differ to what count returns, as it depends on how many pages have been loaded already.

Find single records

find

find finds a unique record by unique identifier (usually id or href). If no record is found an error is raised.

Record.find(123)

GET https://service.example.com/records/123

Record.find('https://anotherservice.example.com/records/123')

GET https://anotherservice.example.com/records/123

find can also be used to find a single unique record with parameters:

Record.find(another_identifier: 456)

GET https://service.example.com/records?another_identifier=456

You can also fetch multiple records by id in parallel:

Record.find(1, 2, 3)

# In parallel:
  GET https://service.example.com/records/1
  GET https://service.example.com/records/2
  GET https://service.example.com/records/3

find_by

find_by finds the first record matching the specified conditions. If no record is found, nil is returned.

find_by! raises DHC::NotFound if nothing was found.

Record.find_by(color: 'blue')

GET https://service.example.com/records?color=blue

first

first is an alias for finding the first record without parameters. If no record is found, nil is returned.

first! raises DHC::NotFound if nothing was found.

Record.first

GET https://service.example.com/records?limit=1

first can also be used with options:

Record.first(params: { color: :blue })

GET https://service.example.com/records?color=blue&limit=1

last

last is an alias for finding the last record without parameters. If no record is found, nil is returned.

last! raises DHC::NotFound if nothing was found.

Record.last

last can also be used with options:

Record.last(params: { color: :blue })

Work with retrieved data

After fetching single or multiple records you can navigate the received data with ease:

records = Record.where(color: 'blue')
records.length # 4
records.count # 400
record = records.first
record.type # 'Business'
record[:type] # 'Business'
record['type'] # 'Business'

Automatic detection/conversion of collections

How to configure endpoints for automatic collection detection?

DHS detects automatically if the responded data is a single business object or a set of business objects (collection).

Conventionally, when the responds contains an items key { items: [] } it's treated as a collection, but also if the responds contains a plain raw array: [{ href: '' }] it's also treated as a collection.

If you need to configure the attribute of the response providing the collection, configure items_key as explained here: Determine collections from the response body

Map complex data for easy access

To influence how data is accessed, simply create methods inside your Record to access complex data structures:

# app/models/record.rb

class Record < DHS::Record

  endpoint '{+service}/records'

  def name
    dig(:addresses, :first, :business, :identities, :first, :name)
  end
end

Access and identify nested records

Nested records, in nested data, are automatically casted to the correct Record class, when they provide an href and that href matches any defined endpoint of any defined Record:

# app/models/place.rb

class Place < DHS::Record
  endpoint '{+service}/places'
  endpoint '{+service}/places/{id}'

  def name
    dig(:addresses, :first, :business, :identities, :first, :name)
  end
end

# app/models/favorite.rb

class Favorite < DHS::Record
  endpoint '{+service}/favorites'
  endpoint '{+service}/favorites/{id}'
end

# app/controllers/some_controller.rb

favorite = Favorite.includes(:place).find(123)
favorite.place.name # depay.fi AG

GET https://service.example.com/favorites/123

{... place: { href: 'https://service.example.com/places/456' }}

GET https://service.example.com/places/456

If automatic detection of nested records does not work, make sure your Records are stored in app/models! See: Insallation/Startup checklist

Relations / Associations

Typically nested data is automatically casted when accessed (See: Access and identify nested records), but sometimes API's don't provide dedicated endpoints to retrieve these records. In those cases, those records are only available through other records and don't have an href on their own and can't be casted automatically, when accessed.

To be able to implement Record-specific logic for those nested records, you can define relations/associations.

has_many

# app/models/location.rb

class Location < DHS::Record

  endpoint '{+service}/locations/{id}'

  has_many :listings

end

# app/models/listing.rb

class Listing < DHS::Record

  def supported?
    type == 'SUPPORTED'
  end
end

# app/controllers/some_controller.rb

Location.find(1).listings.first.supported? # true

GET https://service.example.com/locations/1
{... listings: [{ type: 'SUPPORTED' }] }

class_name: Specify the class name of the relation. Use it only if that name can't be inferred from the relation name. So has_many :photos will by default be linked to the Photo class, but if the real class name is e.g. CustomPhoto or namespaced Custom::Photo, you'll have to specify it with this option.

# app/models/custom/location.rb

module Custom
  class Location < DHS::Record
    endpoint '{+service}/locations'
    endpoint '{+service}/locations/{id}'

    has_many :photos, class_name: 'Custom::Photo'
  end
end

# app/models/custom/photo.rb

module Custom
  class Photo < DHS::Record
  end
end

has_one

# app/models/transaction.rb

class Transaction < DHS::Record

  endpoint '{+service}/transaction/{id}'

  has_one :user
end

# app/models/user.rb

class User < DHS::Record

  def email
    self[:email_address]
  end
end

# app/controllers/some_controller.rb

Transaction.find(1).user.email_address # steve@depay.fi

GET https://service.example.com/transaction/1
{... user: { email_address: 'steve@depay.fi' } }

class_name: Specify the class name of the relation. Use it only if that name can't be inferred from the relation name. So has_many :photos will by default be linked to the Photo class, but if the real class name is e.g. CustomPhoto or namespaced Custom::Photo, you'll have to specify it with this option.

# app/models/custom/location.rb

module Custom
  class Location < DHS::Record
    endpoint '{+service}/locations'
    endpoint '{+service}/locations/{id}'

    has_one :photo, class_name: 'Custom::Photo'
  end
end

# app/models/custom/photo.rb

module Custom
  class Photo < DHS::Record
  end
end

Unwrap nested items from the response body

If the actual item data is mixed with meta data in the response body, DHS allows you to configure a record in a way to automatically unwrap items from within nested response data.

item_key is used to unwrap the actual object from within the response body.

# app/models/location.rb

class Location < DHS::Record
  configuration item_key: [:response, :location]
end

# app/controllers/some_controller.rb

location = Location.find(123)
location.id # 123

GET https://service.example.com/locations/123
{... response: { location: { id: 123 } } }

Determine collections from the response body

items_key key used to determine the collection of items of the current page (e.g. docs, items, etc.), defaults to 'items':

# app/models/search.rb

class Search < DHS::Record
  configuration items_key: :docs
end

# app/controllers/some_controller.rb

search_result = Search.where(q: 'Starbucks')
search_result.first.address # Bahnhofstrasse 5, 8000 Zürich

GET https://service.example.com/search?q=Starbucks
{... docs: [... {...  address: 'Bahnhofstrasse 5, 8000 Zürich' }] }

Load additional data based on retrieved data

In order to load linked data from already retrieved data, you can use load! (or reload!).

# app/controllers/some_controller.rb

record = Record.find(1)
record.associated_thing.load!

GET https://things/4
{ name: "Steve" }

# app/controllers/some_controller.rb
record.associated_thing.name # Steve

record.associated_thing.load! # Does NOT create another request, as it is already loaded
record.associated_thing.reload! # Does request the data again from remote

GET https://things/4
{ name: "Steve" }

Chain complex queries

Method chaining, also known as named parameter idiom, is a common syntax for invoking multiple method calls in object-oriented programming languages. Each method returns an object, allowing the calls to be chained together without requiring variables to store the intermediate results

In order to simplify and enhance preparing complex queries for performing single or multiple requests, DHS implements query chains to find single or multiple records.

DHS query chains do lazy evaluation to only perform as many requests as needed, when the data to be retrieved is actually needed.

Any method, accessing the content of the data to be retrieved, is resolving the chain in place – like .each, .first, .some_attribute_name. Nevertheless, if you just want to resolve the chain in place, and nothing else, fetch should be the method of your choice:

# app/controllers/some_controller.rb

Record.where(color: 'blue').fetch

Chain where queries

# app/controllers/some_controller.rb

records = Record.where(color: 'blue')
[...]
records.where(available: true).each do |record|
  [...]
end

  GET https://service.example.com/records?color=blue&available=true

In case you wan't to check/debug the current values for where in the chain, you can use where_values_hash:

records.where_values_hash

# {color: 'blue', available: true}

Expand plain collections of links: expanded

Some endpoints could respond only with a plain list of links and without any expanded data, like search results.

Use expanded to have DHS expand that data, by performing necessary requests in parallel:

# app/controllers/some_controller.rb

Search.where(what: 'Cafe').expanded

GET https://service.example.com/search?what=Cafe
{...
  "items" : [
    {"href": "https://service.example.com/records/1"},
    {"href": "https://service.example.com/records/2"},
    {"href": "https://service.example.com/records/3"}
  ]
}

In parallel:
  > GET https://service.example.com/records/1
  < {... name: 'Cafe Einstein'}
  > GET https://service.example.com/records/2
  < {... name: 'Starbucks'}
  > GET https://service.example.com/records/3
  < {... name: 'Plaza Cafe'}

{
  ...
  "items" : [
    {
      "href": "https://service.example.com/records/1",
      "name": 'Cafe Einstein',
      ...
    },
    {
      "href": "https://service.example.com/records/2",
      "name": 'Starbucks',
      ...
    },
    {
      "href": "https://service.example.com/records/3",
      "name": 'Plaza Cafe',
      ...
    }
  ]
}

You can also apply request options to expanded. Those options will be used to perform the additional requests to expand the data:

# app/controllers/some_controller.rb

Search.where(what: 'Cafe').expanded(auth: { bearer: access_token })

Error handling with chains

One benefit of chains is lazy evaluation. But that also means they only get resolved when data is accessed. This makes it hard to catch errors with normal rescue blocks:

# app/controllers/some_controller.rb

def show
  @records = Record.where(color: blue) # returns a chain, nothing is resolved, no http requests are performed
rescue => e
  # never ending up here, because the http requests are actually performed in the view, when the query chain is resolved
end

# app/views/some/view.haml

= @records.each do |record| # .each resolves the query chain, leads to http requests beeing performed, which might raises an exception
  = record.name

To simplify error handling with chains, you can also chain error handlers to be resolved, as part of the chain.

If you need to render some different view in Rails based on an DHS error raised during rendering the view, please proceed as following:

# app/controllers/some_controller.rb

def show
  @records = Record
    .rescue(DHC::Error, ->(error){ rescue_from(error) })
    .where(color: 'blue')
  render 'show'
  render_error if @error
end

private

def rescue_from(error)
  @error = error
  nil
end

def render_error
  self.response_body = nil # required to not raise AbstractController::DoubleRenderError
  render 'error'
end

> GET https://service.example.com/records?color=blue
< 406

In case no matching error handler is found the error gets re-raised.

-> Read more about DHC error types/classes

If you want to inject values for the failing records, that might not have been found, you can inject values for them with error handlers:

# app/controllers/some_controller.rb

data = Record
  .rescue(DHC::Unauthorized, ->(response) { Record.new(name: 'unknown') })
  .find(1, 2, 3)

data[1].name # 'unknown'

In parallel:
  > GET https://service.example.com/records/1
  < 200
  > GET https://service.example.com/records/2
  < 400
  > GET https://service.example.com/records/3
  < 200

-> Read more about DHC error types/classes

If an error handler returns nil an empty DHS::Record is returned, not nil!

In case you want to ignore errors and continue working with nil in those cases, please use ignore:

# app/controllers/some_controller.rb

record = Record.ignore(DHC::NotFound).find_by(color: 'blue')

record # nil

Resolve chains: fetch

In case you need to resolve a query chain in place, use fetch:

# app/controllers/some_controller.rb

records = Record.where(color: 'blue').fetch

Add request options to a query chain: options

You can apply options to the request chain. Those options will be forwarded to the request perfomed by the chain/query:

# app/controllers/some_controller.rb

options = { auth: { bearer: '123456' } } # authenticated with OAuth token

# app/controllers/some_controller.rb

AuthenticatedRecord = Record.options(options)

# app/controllers/some_controller.rb

blue_records = AuthenticatedRecord.where(color: 'blue')

GET https://service.example.com/records?color=blue { headers: { 'Authentication': 'Bearer 123456' } }

# app/controllers/some_controller.rb

AuthenticatedRecord.create(color: 'red')

POST https://service.example.com/records { body: '{ color: "red" }' }, headers: { 'Authentication': 'Bearer 123456' } }

# app/controllers/some_controller.rb

record = AuthenticatedRecord.find(123)

GET https://service.example.com/records/123 { headers: { 'Authentication': 'Bearer 123456' } }

# app/controllers/some_controller.rb

authenticated_record = record.options(options) # starting a new chain based on the found record

# app/controllers/some_controller.rb

authenticated_record.valid?

POST https://service.example.com/records/validate { body: '{...}', headers: { 'Authentication': 'Bearer 123456' } }

# app/controllers/some_controller.rb

authenticated_record.save

POST https://service.example.com/records { body: '{...}', headers: { 'Authentication': 'Bearer 123456' } }

# app/controllers/some_controller.rb

authenticated_record.destroy

DELETE https://service.example.com/records/123 { headers: { 'Authentication': 'Bearer 123456' } }

# app/controllers/some_controller.rb

authenticated_record.update(name: 'Steve')

POST https://service.example.com/records/123 { body: '{...}', headers: { 'Authentication': 'Bearer 123456' } }

Control pagination within a query chain

page sets the page that you want to request.

per sets the amount of items requested per page.

limit is an alias for per. But without providing arguments, it resolves the query and provides the current response limit per page

# app/controllers/some_controller.rb

Record.page(3).per(20).where(color: 'blue')

GET https://service.example.com/records?offset=40&limit=20&color=blue

# app/controllers/some_controller.rb

Record.page(3).per(20).where(color: 'blue')

GET https://service.example.com/records?offset=40&limit=20&color=blue

The applied pagination strategy depends on whats configured for the particular record: See Record pagination

Record pagination

You can configure pagination on a per record base. DHS differentiates between the pagination strategy (how items/pages are navigated and calculated) and pagination keys (how stuff is named and accessed).

Pagination strategy

Pagination strategy: offset (default)

The offset pagination strategy is DHS's default pagination strategy, so nothing needs to be (re-)configured.

The offset pagination strategy starts with 0 and offsets by the amount of items, thay you've already recived – typically limit.

# app/models/record.rb

class Search < DHS::Record
  endpoint '{+service}/search'
end

# app/controllers/some_controller.rb

Record.all

GET https://service.example.com/records?limit=100
{
  items: [{...}, ...],
  total: 300,
  limit: 100,
  offset: 0
}
In parallel:
  GET https://service.example.com/records?limit=100&offset=100
  GET https://service.example.com/records?limit=100&offset=200

Pagination strategy: page

In comparison to the offset strategy, the page strategy just increases by 1 (page) and sends the next batch of items for the next page.

# app/models/record.rb

class Search < DHS::Record
  configuration pagination_strategy: 'page', pagination_key: 'page'

  endpoint '{+service}/search'
end

# app/controllers/some_controller.rb

Record.all

GET https://service.example.com/records?limit=100
{
  items: [{...}, ...],
  total: 300,
  limit: 100,
  page: 1
}
In parallel:
  GET https://service.example.com/records?limit=100&page=2
  GET https://service.example.com/records?limit=100&page=3

Pagination strategy: offset_page

The offest_page strategy is based on the page strategy with the only difference that the pages are counted from 0 onwards (not from 1).

# app/models/transaction.rb

class Transaction < DHS::Record
  configuration pagination_strategy: 'offset_page', pagination_key: 'page'

  endpoint '{+service}/transactions'
end

# app/controllers/some_controller.rb

Record.all

GET https://service.example.com/records?limit=100
{
  items: [{...}, ...],
  total: 300,
  limit: 100,
  page: 0
}
In parallel:
  GET https://service.example.com/records?limit=100&page=1
  GET https://service.example.com/records?limit=100&page=2

Pagination strategy: total_pages

The total_pages strategy is based on the page strategy with the only difference that the responding api provides total_pages over total_items.

# app/models/transaction.rb

class Transaction < DHS::Record
  configuration pagination_strategy: 'total_pages', pagination_key: 'page', total_key: 'total_pages'

  endpoint '{+service}/transactions'
end

# app/controllers/some_controller.rb

Record.all

GET https://service.example.com/transactions?limit=100
{
  items: [{...}, ...],
  total_pages: 3,
  limit: 100,
  page: 1
}
In parallel:
  GET https://service.example.com/records?limit=100&page=2
  GET https://service.example.com/records?limit=100&page=3

Pagination strategy: start

In comparison to the offset strategy, the start strategy indicates with which item the current page starts. Typically it starts with 1 and if you get 100 items per page, the next start is 101.

# app/models/record.rb

class Search < DHS::Record
  configuration pagination_strategy: 'start', pagination_key: 'startAt'

  endpoint '{+service}/search'
end

# app/controllers/some_controller.rb

Record.all

GET https://service.example.com/records?limit=100
{
  items: [{...}, ...],
  total: 300,
  limit: 100,
  page: 1
}
In parallel:
  GET https://service.example.com/records?limit=100&startAt=101
  GET https://service.example.com/records?limit=100&startAt=201

Pagination strategy: link

The link strategy continuously follows in-response embedded links to following pages until the last page is reached (indicated by no more next link).

WARNING

Loading all pages from a resource paginated with links only can result in very poor performance, as pages can only be loaded sequentially!

# app/models/record.rb

class Search < DHS::Record
  configuration pagination_strategy: 'link'

  endpoint '{+service}/search'
end

# app/controllers/some_controller.rb

Record.all

GET https://service.example.com/records?limit=100
{
  items: [{...}, ...],
  limit: 100,
  next: {
    href: 'https://service.example.com/records?from_record_id=p62qM5p0NK_qryO52Ze-eg&limit=100'
  }
}
Sequentially:
  GET https://service.example.com/records?from_record_id=p62qM5p0NK_qryO52Ze-eg&limit=100
  GET https://service.example.com/records?from_record_id=xcaoXBmuMyFFEcFDSgNgDQ&limit=100

Pagination strategy: next_offset

The next_offset strategy continuously follows in-response offset information to following pages until the last page is reached (indicated by next offset being either empty or 0).

WARNING

Loading all pages from a resource paginated with next_offset only can result in very poor performance, as pages can only be loaded sequentially!

# app/models/record.rb

class Search < DHS::Record
  configuration pagination_strategy: 'next_offset'

  endpoint '{+service}/assets'
end

# app/controllers/some_controller.rb

Record.all

GET https://service.example.com/assets?limit=100
{
  items: [{...}, ...],
  limit: 10,
  next_offset: 29
}
GET https://service.example.com/assets?offset=29
{
  items: [{...}, ...],
  limit: 10,
  next_offset: 39
}
GET https://service.example.com/assets?offset=39
{
  items: [{...}, ...],
  limit: 10,
  next_offset: 0
}

Pagination strategy: next_parameter

The next_parameter strategy continuously follows in-response offset parameter information to following pages until the last page is reached (indicated by next parameter being empty or unset).

WARNING

Loading all pages from a resource paginated with next_parameter only can result in very poor performance, as pages can only be loaded sequentially!

# app/models/record.rb

class Search < DHS::Record
  configuration pagination_strategy: 'next_parameter'

  endpoint '{+service}/assets'
end

# app/controllers/some_controller.rb

Record.all

GET https://service.example.com/assets?limit=100
{
  items: [{...}, ...],
  limit: 10,
  next: "LXBrPTIzMzE4NDE0"
}
GET https://service.example.com/assets?next=LXBrPTIzMzE4NDE0
{
  items: [{...}, ...],
  limit: 10,
  next: "ASDASdads9123"
}
GET https://service.example.com/assets?next=ASDASdads9123
{
  items: [{...}, ...],
  limit: 10
}

Pagination keys

limit_key

limit_key sets the key used to indicate how many items you want to retrieve per page e.g. size, limit, etc. In case the limit_key parameter differs for how it needs to be requested from how it's provided in the reponse, use body and parameter subkeys.

# app/models/record.rb

class Record < DHS::Record
  configuration limit_key: { body: [:pagination, :max], parameter: :max }

  endpoint '{+service}/records'
end

# app/controllers/some_controller.rb

records = Record.where(color: 'blue')
records.limit # 20

GET https://service.example.com/records?color=blue&max=100
{ ...
  items: [...],
  pagination: { max: 20 }
}

pagination_key

pagination_key defines which key to use to paginate a page (e.g. offset, page, startAt etc.). In case the limit_key parameter differs for how it needs to be requested from how it's provided in the reponse, use body and parameter subkeys.

# app/models/record.rb

class Record < DHS::Record
  configuration pagination_key: { body: [:pagination, :page], parameter: :page }, pagination_strategy: :page

  endpoint '{+service}/records'
end

# app/controllers/some_controller.rb

records = Record.where(color: 'blue').all
records.length # 300

GET https://service.example.com/records?color=blue&limit=100
{... pagination: { page: 1 } }
In parallel:
  GET https://service.example.com/records?color=blue&limit=100&page=2
  {... pagination: { page: 2 } }
  GET https://service.example.com/records?color=blue&limit=100&page=3
  {... pagination: { page: 3 } }

total_key

total_key defines which key to user for pagination to describe the total amount of remote items (e.g. total, totalResults, etc.).

# app/models/record.rb

class Record < DHS::Record
  configuration total_key: [:pagination, :total]

  endpoint '{+service}/records'
end

# app/controllers/some_controller.rb

records = Record.where(color: 'blue').fetch
records.length # 100
records.count # 300

GET https://service.example.com/records?color=blue&limit=100
{... pagination: { total: 300 } }

Pagination links

next?

next? Tells you if there is a next link or not.

# app/controllers/some_controller.rb

@records = Record.where(color: 'blue').fetch

GET https://service.example.com/records?color=blue&limit=100
{... items: [...], next: 'https://service.example.com/records?color=blue&limit=100&offset=100' }

# app/views/some_view.haml

- if @records.next?
  = render partial: 'next_arrow'

previous?

previous? Tells you if there is a previous link or not.

# app/controllers/some_controller.rb

@records = Record.where(color: 'blue').fetch

GET https://service.example.com/records?color=blue&limit=100
{... items: [...], previous: 'https://service.example.com/records?color=blue&limit=100&offset=100' }

# app/views/some_view.haml

- if @records.previous?
  = render partial: 'previous_arrow'

Kaminari support (limited)

DHS implements an interface that makes it partially working with Kaminari.

The kaminari’s page parameter is in params[:page]. For example, you can use kaminari to render paginations based on DHS Records. Typically, your code will look like this:

# controller
@items = Record.page(params[:page]).per(100)

# view
= paginate @items

Build, create and update records

Create new records

create

create will return the object in memory if persisting fails, providing validation errors in .errors (See record validation).

create! instead will raise an exception.

create always builds the data of the local object first, before it tries to sync with an endpoint. So even if persisting fails, the local object is build.

# app/controllers/some_controller.rb

record = Record.create(
  text: 'Hello world'
)

POST https://service.example.com/records { body: "{ 'text' : 'Hello world' }" }

-> See record validation for how to handle validation errors when creating records.

Unwrap nested data when creation response nests created record data

item_created_key key used to merge record data thats nested in the creation response body:

# app/models/location.rb

class Location < DHS::Record

  configuration item_created_key: [:response, :location]

end

# app/controllers/some_controller.rb

location.create(lat: '47.3920152', long: '8.5127981')
location.address # Förrlibuckstrasse 62, 8005 Zürich

POST https://service.example.com/locations { body: "{ 'lat': '47.3920152', long: '8.5127981' }" }
{... { response: { location: {... address: 'Förrlibuckstrasse 62, 8005 Zürich' } } } } 

Create records through associations: Nested sub resources

# app/models/restaurant.rb

class Restaurant < DHS::Record
  endpoint '{+service}/restaurants/{id}'
end

# app/models/feedback.rb

class Feedback < DHS::Record
  endpoint '{+service}/restaurants/{restaurant_id}/feedbacks'
end

# app/controllers/some_controller.rb

restaurant = Restaurant.find(1)

GET https://service.example.com/restaurants/1
{... reviews: { href: 'https://service.example.com/restaurants/1/reviews' }}

# app/controllers/some_controller.rb

restaurant.reviews.create(
  text: 'Simply awesome!'
)

POST https://service.example.com/restaurants/1/reviews { body: "{ 'text': 'Simply awesome!' }" }

Start building new records

With new or build you can start building new records from scratch, which can be persisted with save:

# app/controllers/some_controller.rb

record = Record.new # or Record.build
record.name = 'Starbucks'
record.save

POST https://service.example.com/records { body: "{ 'name' : 'Starbucks' }" }

Change/Update existing records

save

save persist the whole object in it's current state.

save will return false if persisting fails. save! instead will raise an exception.

# app/controllers/some_controller.rb

record = Record.find('1z-5r1fkaj')

GET https://service.example.com/records/1z-5r1fkaj
{ name: 'Starbucks', recommended: null }

# app/controllers/some_controller.rb

record.recommended = true
record.save

POST https://service.example.com/records/1z-5r1fkaj { body: "{ 'name': 'Starbucks', 'recommended': true }" }

-> See record validation for how to handle validation errors when updating records.

update

Directly via Record

# app/controllers/some_controller.rb

Record.update(id: '1z-5r1fkaj', name: 'Steve')

GET https://service.example.com/records/1z-5r1fkaj
{ name: 'Steve' }

per Instance

update persists the whole object after new parameters are applied through arguments.

update will return false if persisting fails. update! instead will raise an exception.

update always updates the data of the local object first, before it tries to sync with an endpoint. So even if persisting fails, the local object is updated.

# app/controllers/some_controller.rb

record = Record.find('1z-5r1fkaj')

GET https://service.example.com/records/1z-5r1fkaj
{ name: 'Starbucks', recommended: null }

# app/controllers/some_controller.rb

record.update(recommended: true)

POST https://service.example.com/records/1z-5r1fkaj { body: "{ 'name': 'Starbucks', 'recommended': true }" }

-> See record validation for how to handle validation errors when updating records.

You can use update and the end of query-chains:

# app/controllers/some_controller.rb

record.options(method: :put).update(recommended: true)

You can also pass explicit request options to update, by passing two explicit hashes:

# app/controllers/some_controller.rb

record.update({ recommended: true }, { method: 'put' })

partial_update

partial_update updates just the provided parameters.

partial_update will return false if persisting fails. partial_update! instead will raise an exception.

partial_update always updates the data of the local object first, before it tries to sync with an endpoint. So even if persisting fails, the local object is updated.

# app/controllers/some_controller.rb

record = Record.find('1z-5r1fkaj')

GET https://service.example.com/records/1z-5r1fkaj
{ name: 'Starbucks', recommended: null }

# app/controllers/some_controller.rb

record.partial_update(recommended: true)

POST https://service.example.com/records/1z-5r1fkaj { body: "{ 'recommended': true }" }

-> See record validation for how to handle validation errors when updating records.

You can use partial_update at the end of query-chains:

# app/controllers/some_controller.rb

record.options(method: :put).partial_update(recommended: true)

You can also pass explicit request options to partial_update, by passing two explicit hashes:

# app/controllers/some_controller.rb

record.partial_update({ recommended: true }, { method: 'put' })

Endpoint url parameter injection during record creation/change

DHS injects parameters provided to create, update, partial_update, save etc. into an endpoint's URL when matching:

# app/models/feedback.rb

class Feedback << DHS::Record
  endpoint '{+service}/records/{record_id}/feedbacks'
end

# app/controllers/some_controller.rb

Feedback.create(record_id: 51232, text: 'Great Restaurant!')

POST https://service.example.com/records/51232/feedbacks { body: "{ 'text' : 'Great Restaurant!' }" }

Record validation

In order to validate records before persisting them, you can use the valid? (validate alias) method.

It's not recommended to validate records anywhere, including application side validation via ActiveModel::Validations, except, if you validate them via the same endpoint/service, that also creates them.

The specific endpoint has to support validations without persistence. An endpoint has to be enabled (opt-in) in your record configurations:

# app/models/user.rb

class User < DHS::Record

  endpoint '{+service}/users', validates: { params: { persist: false } }

end

# app/controllers/some_controller.rb

user = User.build(email: 'i\'m not an email address')

unless user.valid?
  @errors = user.errors
  render 'new' and return
end

POST https://service.example.com/users?persist=false { body: '{ "email" : "i'm not an email address"}' }
{ 
  "field_errors": [{
    "path": ["email"],
    "code": "WRONG_FORMAT",
    "message": "The property value's format is incorrect."
  }],
  "message": "Email must have the correct format."
}

The functionalities of DHS::Errors pretty much follow those of ActiveModel::Validation:

# app/views/some_view.haml

@errors.any? # true
@errors.include?(:email) # true
@errors[:email] # ['WRONG_FORMAT']
@errors.messages # {:email=>["Translated error message that this value has the wrong format"]}
@errors.codes # {:email=>["WRONG_FORMAT"]}
@errors.message # Email must have the correct format."

Configure record validations

The parameters passed to the validates endpoint option are used to perform record validations:

# app/models/user.rb

class User < DHS::Record

  endpoint '{+service}/users', validates: { params: { persist: false } }  # will add ?persist=false to the request
  endpoint '{+service}/users', validates: { params: { publish: false } }  # will add ?publish=false to the request
  endpoint '{+service}/users', validates: { params: { validates: true } } # will add ?validates=true to the request
  endpoint '{+service}/users', validates: { path: 'validate' }            # will perform a validation via ...users/validate

end

HTTP Status Codes for validation errors

The HTTP status code received from the endpoint when performing validations on a record, is available through the errors object:

# app/controllers/some_controller.rb

record.save
record.errors.status_code # 400

Reset validation errors

Clear the error messages like:

# app/controllers/some_controller.rb

record.errors.clear

Add validation errors

In case you want to add application side validation errors, even though it's not recommended, do it as following:

user.errors.add(:name, 'WRONG_FORMAT')

Validation errors for nested data

If you work with complex data structures, you sometimes need to have validation errors delegated/scoped to nested data.

This features makes DHS::Records compatible with how Rails or Simpleform renders/builds forms and especially error messages:

# app/controllers/some_controller.rb

unless @customer.save
  @errors = @customer.errors
end

POST https://service.example.com/customers { body: "{ 'address' : { 'street': 'invalid', housenumber: '' } }" }
{ 
  "field_errors": [{
    "path": ["address", "street"],
    "code": "REQUIRED_PROPERTY_VALUE_INCORRECT",
    "message": "The property value is incorrect."
  },{
    "path": ["address", "housenumber"],
    "code": "REQUIRED_PROPERTY_VALUE",
    "message": "The property value is required."
  }],
  "message": "Some data is invalid."
}

# app/views/some_view.haml

= form_for @customer, as: :customer do |customer_form|

  = fields_for 'customer[:address]', @customer.address, do |address_form|

    = fields_for 'customer[:address][:street]', @customer.address.street, do |street_form|

      = street_form.input :name
      = street_form.input :house_number

This would render nested forms and would also render nested form errors for nested data structures.

You can also access those nested errors like:

@customer.address.errors
@customer.address.street.errors

Translation of validation errors

If a translation exists for one of the following translation keys, DHS will provide a translated error (also in the following order) rather than the plain error message/code, when building forms or accessing @errors.messages:

dhs.errors.records.<record_name>.attributes.<attribute_name>.<error_code>
e.g. dhs.errors.records.customer.attributes.name.unsupported_property_value

dhs.errors.records.<record_name>.<error_code>
e.g. dhs.errors.records.customer.unsupported_property_value

dhs.errors.messages.<error_code>
e.g. dhs.errors.messages.unsupported_property_value

dhs.errors.attributes.<attribute_name>.<error_code>
e.g. dhs.errors.attributes.name.unsupported_property_value

dhs.errors.fallback_message

dhs.errors.records.<record_name>.attributes.<collection>.<attribute_name>.<error_code>
e.g. dhs.errors.records.appointment_proposal.attributes.appointments.date_time.date_property_not_in_future

Validation error types: errors vs. warnings

Persistance failed: errors

If an endpoint returns errors in the response body, that is enough to interpret it as: persistance failed. The response status code in this scenario is neglected.

Persistance succeeded: warnings

In some cases, you need non blocking meta information about potential problems with the created record, so called warnings.

If the API endpoint implements warnings, returned when validating, they are provided just as errors (same interface and methods) through the warnings attribute:

# app/controllres/some_controller.rb

@presence = Presence.options(params: { synchronize: false }).create(
  place: { href: 'http://storage/places/1' }
)

POST https://service.example.com/presences { body: '{ "place": { "href": "http://storage/places/1" } }' }
{
    field_warnings: [{
      code: 'WILL_BE_RESIZED',
      path: ['place', 'photos', 0],
      message: 'This photo is too small and will be resized.'
    }
  }

presence.warnings.any? # true
presence.place.photos[0].warnings.messages.first # 'This photo is too small and will be resized.'

Using ActiveModel::Validations none the less

If you are using ActiveModel::Validations, even though it's not recommended, and you add errors to the DHS::Record instance, then those errors will be overwritten by the errors from ActiveModel::Validations when using save or valid?.

So in essence, mixing ActiveModel::Validations and DHS built-in validations (via endpoints), is not compatible, yet.

Open issue

Use form_helper to create and update records

Rails form_for view-helper can be used in combination with instances of DHS::Records to autogenerate forms:

<%= form_for(@instance, url: '/create') do |f| %>
  <%= f.text_field :name %>
  <%= f.text_area :text %>
  <%= f.submit "Create" %>
<% end %>

Destroy records

destroy deletes a record.

# app/controllers/some_controller.rb

record = Record.find('1z-5r1fkaj')

GET https://service.example.com/records/1z-5r1fkaj

# app/controllers/some_controller.rb

record.destroy

DELETE https://service.example.com/records/1z-5r1fkaj

You can also destroy records directly without fetching them first:

# app/controllers/some_controller.rb

destroyed_record = Record.destroy('1z-5r1fkaj')

DELETE https://service.example.com/records/1z-5r1fkaj

or with parameters:

# app/controllers/some_controller.rb

destroyed_records = Record.destroy(name: 'Steve')

DELETE https://service.example.com/records?name='Steve'

Record getters and setters

Sometimes it is neccessary to implement custom getters and setters and convert data to a processable (endpoint) format behind the scenes.

Record setters

You can define setter methods in DHS::Records that will be used by initializers (new) and setter methods, that convert data provided, before storing it in the record and persisting it with a remote endpoint:

# app/models/user.rb

class Feedback < DHS::Record

  def ratings=(values)
    super(
      values.map { |k, v| { name: k, value: v } }
    )
  end
end

# app/controllers/some_controller.rb

record = Record.new(ratings: { quality: 3 })
record.ratings # [{ :name=>:quality, :value=>3 }]

Setting attributes with other names:

# app/models/booking.rb

class Booking < DHS::Record

  def appointments_attributes=(values)
    self.appointments = values.map { |appointment| appointment[:id] }
  end
end

or

# app/models/booking.rb

class Booking < DHS::Record

  def appointments_attributes=(values)
    self[:appointments] = values.map { |appointment| appointment[:id] }
  end
end

# app/controllers/some_controller.rb

booking.update(params)

Record getters

If you implement accompanying getter methods, the whole data conversion would be internal only:

# app/models/user.rb

class Feedback < DHS::Record

  def ratings=(values)
    super(
      values.map { |k, v| { name: k, value: v } }
    )
  end

  def ratings
    super.map { |r| [r[:name], r[:value]] }]
  end
end

# app/controllers/some_controller.rb

record = Record.new(ratings: { quality: 3 })
record.ratings # {:quality=>3}

Include linked resources (hyperlinks and hypermedia)

In a service-oriented architecture using hyperlinks/hypermedia, records/resources can contain hyperlinks to other records/resources.

When fetching records with DHS, you can specify in advance all the linked resources that you want to include in the results.

With includes DHS ensures that all matching and explicitly linked resources are loaded and merged (even if the linked resources are paginated).

Including linked resources/records is heavily influenced by https://guides.rubyonrails.org/active_record_querying.html and you should read it to understand this feature in all it's glory.

Generate links from parameters

Sometimes you need to generate full hrefs/urls for records but you just have parameters that describe that record, like the ID.

For those usecases you can use href_for(params):

# app/controllers/some_controller.rb

Presence.create(place: { href: Place.href_for(123) })

POST '/presences' { place: { href: "http://datastore/places/123" } }

Ensure the whole linked collection is included with includes

In case endpoints are paginated and you are certain that you'll need all objects of a set and not only the first page/batch, use includes.

DHS will ensure that all linked resources are around by loading all pages (parallelized/performance optimized).

# app/controllers/some_controller.rb

customer = Customer.includes(contracts: :products).find(1)

> GET https://service.example.com/customers/1
< {... contracts: { href: 'https://service.example.com/customers/1/contracts' } }
> GET https://service.example.com/customers/1/contracts?limit=100
< {... items: [...], limit: 10, offset: 0, total: 32 }
In parallel: 
  > GET https://service.example.com/customers/1/contracts?limit=10&offset=10
  < {... products: [{ href: 'https://service.example.com/product/LBC' }] }
  > GET https://service.example.com/customers/1/contracts?limit=10&offset=20
  < {... products: [{ href: 'https://service.example.com/product/LBB' }] }
In parallel:
  > GET https://service.example.com/product/LBC
  < {... name: 'Local Business Card' }
  > GET https://service.example.com/product/LBB
  < {... name: 'Local Business Basic' }

# app/controllers/some_controller.rb

customer.contracts.length # 32
customer.contracts.first.products.first.name # Local Business Card

Include only the first linked page of a linked collection: includes_first_page

includes_first_page includes the first page/response when loading the linked resource. If the endpoint is paginated, only the first page will be included.

# app/controllers/some_controller.rb

customer = Customer.includes_first_page(contracts: :products).find(1)

> GET https://service.example.com/customers/1
< {... contracts: { href: 'https://service.example.com/customers/1/contracts' } }
> GET https://service.example.com/customers/1/contracts?limit=100
< {... items: [...], limit: 10, offset: 0, total: 32 }
In parallel:
  > GET https://service.example.com/product/LBC
  < {... name: 'Local Business Card' }
  > GET https://service.example.com/product/LBB
  < {... name: 'Local Business Basic' }

# app/controllers/some_controller.rb

customer.contracts.length # 10
customer.contracts.first.products.first.name # Local Business Card

Include various levels of linked data

The method syntax of includes allows you include hyperlinks stored in deep nested data strutures:

Some examples:

Record.includes(:depay_account, :entry)
# Includes depay_account -> entry
# { depay_account: { href: '...', entry: { href: '...' } } }

Record.includes([:depay_account, :entry])
# Includes depay_account and entry
# { depay_account: { href: '...' }, entry: { href: '...' } }

Record.includes(campaign: [:entry, :user])
# Includes campaign and entry and user from campaign
# { campaign: { href: '...' , entry: { href: '...' }, user: { href: '...' } } }

Identify and cast known records when including records

When including linked resources with includes, already defined records and their endpoints and configurations are used to make the requests to fetch the additional data.

That also means that options for endpoints of linked resources are applied when requesting those in addition.

This applies for example a records endpoint configuration even though it's fetched/included through another record:

# app/models/favorite.rb

class Favorite < DHS::Record

  endpoint '{+service}/users/{user_id}/favorites', auth: { basic: { username: 'steve', password: 'can' } }
  endpoint '{+service}/users/{user_id}/favorites/:id', auth: { basic: { username: 'steve', password: 'can' } }

end

# app/models/place.rb

class Place < DHS::Record

  endpoint '{+service}/v2/places', auth: { basic: { username: 'steve', password: 'can' } }
  endpoint '{+service}/v2/places/{id}', auth: { basic: { username: 'steve', password: 'can' } }

end

# app/controllers/some_controller.rb

Favorite.includes(:place).where(user_id: current_user.id)

> GET https://service.example.com/users/123/favorites { headers: { 'Authentication': 'Basic c3RldmU6Y2Fu' } }
< {... items: [... { place: { href: 'https://service.example.com/place/456' } } ] }
In parallel:
  > GET https://service.example.com/place/456 { headers: { 'Authentication': 'Basic c3RldmU6Y2Fu' } }
  > GET https://service.example.com/place/789 { headers: { 'Authentication': 'Basic c3RldmU6Y2Fu' } }
  > GET https://service.example.com/place/1112 { headers: { 'Authentication': 'Basic c3RldmU6Y2Fu' } }
  > GET https://service.example.com/place/5423 { headers: { 'Authentication': 'Basic c3RldmU6Y2Fu' } }

Apply options for requests performed to fetch included records

Use references to apply request options to requests performed to fetch included records:

# app/controllers/some_controller.rb

Favorite.includes(:place).references(place: { auth: { bearer: '123' }}).where(user_id: 1)

GET https://service.example.com/users/1/favorites
{... items: [... { place: { href: 'https://service.example.com/places/2' } }] }
In parallel:
  GET https://service.example.com/places/2 { headers: { 'Authentication': 'Bearer 123' } }
  GET https://service.example.com/places/3 { headers: { 'Authentication': 'Bearer 123' } }
  GET https://service.example.com/places/4 { headers: { 'Authentication': 'Bearer 123' } }

Here is another example, if you want to ignore errors, that occure while you fetch included resources:

# app/controllers/some_controller.rb

feedback = Feedback
  .includes(campaign: :entry)
  .references(campaign: { ignore: DHC::NotFound })
  .find(12345)

compact: Remove included resources that didn't return any records

In case you include nested data and ignored errors while including, it can happen that you get back a collection that contains data based on response errors:

# app/controllers/some_controller.rb

user = User
  .includes(:places)
  .references(places: { ignore: DHC::NotFound })
  .find(123)

GET http://service/users/123
{ "places": { "href": "http://service/users/123/places" } }

GET http://service/users/123/places
{ "items": [
  { "href": "http://service/places/1" },
  { "href": "http://service/places/2" }
] }

GET http://service/places/1
200 { "name": "Casa Ferlin" }

GET http://service/places/2
404 { "status": 404, "error": "not found" }

user.places[1] # { "status": 404, "error": "not found" }

In order to exclude items from a collection which where not based on successful responses, use .compact or .compact!:

# app/controllers/some_controller.rb

user = User
  .includes(:places)
  .references(places: { ignore: DHC::NotFound })
  .find(123)
places = user.places.compact

places # { "items": [ { "href": "http://service/places/1", "name": "Casa Ferlin" } ] }

Record batch processing

Be careful using methods for batch processing. They could result in a lot of HTTP requests!

all

all fetches all records from the service by doing multiple requests, best-effort parallelization, and resolving endpoint pagination if necessary:

records = Record.all

> GET https://service.example.com/records?limit=100
< {...
  items: [...]
  total: 900,
  limit: 100,
  offset: 0
}
In parallel:
  > GET https://service.example.com/records?limit=100&offset=100
  > GET https://service.example.com/records?limit=100&offset=200
  > GET https://service.example.com/records?limit=100&offset=300
  > GET https://service.example.com/records?limit=100&offset=400
  > GET https://service.example.com/records?limit=100&offset=500
  > GET https://service.example.com/records?limit=100&offset=600
  > GET https://service.example.com/records?limit=100&offset=700
  > GET https://service.example.com/records?limit=100&offset=800

all is chainable and has the same interface like where:

Record.where(color: 'blue').all
Record.all.where(color: 'blue')
Record.all(color: 'blue')

All three are doing the same thing: fetching all records with the color 'blue' from the endpoint while resolving pagingation if endpoint is paginated.

Using all, when endpoint does not implement response pagination meta data

In case an API does not provide pagination information in the repsponse data (limit, offset and total), DHS keeps on loading pages when requesting all until the first empty page responds.

find_each

find_each is a more fine grained way to process single records that are fetched in batches.

Record.find_each(start: 50, batch_size: 20, params: { has_reviews: true }, headers: { 'Authorization': 'Bearer 123' }) do |record|
  # Iterates over each record. Starts with record no. 50 and fetches 20 records each batch.
  record
  break if record.some_attribute == some_value
end

find_in_batches

find_in_batches is used by find_each and processes batches.

Record.find_in_batches(start: 50, batch_size: 20, params: { has_reviews: true }, headers: { 'Authorization': 'Bearer 123' }) do |records|
  # Iterates over multiple records (batch size is 20). Starts with record no. 50 and fetches 20 records each batch.
  records
  break if records.first.name == some_value
end

Convert/Cast specific record types: becomes

Based on ActiveRecord's implementation, DHS implements becomes, too.

It's a way to convert records of a certain type A to another certain type B.

NOTE: RPC-style actions, that are discouraged in REST anyway, are utilizable with this functionality, too. See the following example:

# app/models/location.rb

class Location < DHS::Record
  endpoint '{+service}/locations'
  endpoint '{+service}/locations/{id}'
end

# app/models/synchronization.rb

class Synchronization < DHS::Record
  endpoint '{+service}/locations/{id}/sync'
end

# app/controllers/some_controller.rb

location = Location.find(1)

GET https://service.example.com/location/1

# app/controllers/some_controller.rb

synchronization = location.becomes(Synchronization)
synchronization.save!

POST https://service.example.com/location/1/sync { body: '{ ... }' }

Assign attributes

Allows you to set the attributes by passing in a hash of attributes.

entry = LocalEntry.new
entry.assign_attributes(company_name: 'DePay')
entry.company_name # => 'DePay'

Request Cycle Cache

By default, DHS does not perform the same http request multiple times during one request/response cycle.

# app/models/user.rb

class User < DHS::Record
  endpoint '{+service}/users/{id}'
end

# app/models/location.rb

class Location < DHS::Record
  endpoint '{+service}/locations/{id}'
end

# app/controllers/some_controller.rb

def index
  @user = User.find(1)
  @locations = Location.includes(:owner).find(2)
end

GET https://service.example.com/users/1
GET https://service.example.com/location/2
{... owner: { href: 'https://service.example.com/users/1' } }
From cache:
  GET https://service.example.com/users/1

It uses the DHC Caching Interceptor as caching mechanism base and sets a unique request id for every request cycle with Railties to ensure data is just cached within one request cycle and not shared with other requests.

Only GET requests are considered for caching by using DHC Caching Interceptor's cache_methods option internally and considers request headers when caching requests, so requests with different headers are not served from cache.

The DHS Request Cycle Cache is opt-out, so it's enabled by default and will require you to enable the DHC Caching Interceptor in your project.

Change store for DHS' request cycle cache

By default the DHS Request Cycle Cache will use ActiveSupport::Cache::MemoryStore as its cache store. Feel free to configure a cache that is better suited for your needs by:

# config/initializers/dhs.rb

DHS.configure do |config|
  config.request_cycle_cache = ActiveSupport::Cache::MemoryStore.new
end

Disable request cycle cache

If you want to disable the DHS Request Cycle Cache, simply disable it within configuration:

# config/initializers/dhs.rb

DHS.configure do |config|
  config.request_cycle_cache_enabled = false
end

Automatic Authentication (OAuth)

DHS provides a way to have records automatically fetch and use OAuth authentication when performing requests within Rails.

In order to enable automatic oauth authentication, perform the following steps:

1. Make sure DHS is configured to perform auto_oauth. Provide a block that, when executed in the controller context, returns a valid access_token/bearer_token. ```ruby # config/initializers/dhs.rb

DHS.configure do |config| config.auto_oauth = -> { access_token } end

2. Opt-in records requiring oauth authentication:

```ruby
# app/models/record.rb

class Record < DHS::Record
  oauth
  # ...
end

1. Include the DHS::OAuth context into your application controller:

# app/controllers/application_controller.rb

class ApplicationController < ActionController::Base
  include DHS::OAuth

  # ...
end

1. Make sure you have the DHC::Auth interceptor enabled:

# config/initializers/dhc.rb

DHC.configure do |config|
  config.interceptors = [DHC::Auth]
end

Now you can perform requests based on the record that will be auto authenticated from now on:

# app/controllers/some_controller.rb

Record.find(1)

https://records/1
Authentication: 'Bearer token-12345'

Configure multiple auth providers (even per endpoint)

In case you need to configure multiple auth provider access_tokens within your application, make sure you provide a proc returning a hash when configuring auto_oauth, naming every single provider and the responsive method to retrieve the access_tokens in the controller context:

# config/initializers/dhs.rb
DHS.configure do |config|
  config.auto_oauth = proc do
    {
      provider1: access_token_provider_1,
      provider2: access_token_provider_2
    }
  end
end

Then make sure you either define which provider to use on a record level:

# model/record.rb
class Record < DHS::Record
  oauth(:provider1)
  #...
end

or on an endpoint level:

# model/record.rb
class Record < DHS::Record
  endpoint 'https://service/records', oauth: :provider1
  #...
end

Configure providers

If you're using DHS service providers, you can also configure auto auth on a provider level:

# app/models/providers/depay.rb
module Providers
  class Depay < DHS::Record

    provider(
      oauth: true
    )
  end
end

or with multiple auth providers:

# app/models/providers/depay.rb
module Providers
  class Depay < DHS::Record

    provider(
      oauth: :provider_1
    )
  end
end

Option Blocks

In order to apply options to all requests performed in a give block, DHS provides option blocks.

# app/controllers/records_controller.rb

DHS.options(headers: { 'Tracking-Id' => 123 }) do
  Record.find(1)
end

Record.find(2)

GET https://records/1 { headers: { 'Tracking-Id' => '123' } }
GET https://records/2 { headers: { } }

Request tracing

DHS supports tracing the source (in your application code) of http requests being made with methods like find find_by find_by! first first! last last!.

Following links, and using includes are not traced (just yet).

In order to enable tracing you need to enable it via DHS configuration:

# config/initializers/dhs.rb

DHS.configure do |config|
  config.trace = Rails.env.development? || Rails.logger.level == 0 # debug
end

# app/controllers/application_controller.rb

code = Code.find(code: params[:code])

Called from onboarding/app/controllers/concerns/access_code_concern.rb:11:in `access_code'

However, following links and includes won't get traced (just yet):

# app/controllers/application_controller.rb

code = Code.includes(:places).find(123)

# Nothing is traced
{
  places: [...]
}

code.places

{ 
  token: "XYZABCDEF",
  places:
    [
      { href: "http://storage-stg.preprod-depay.fi/v2/places/egZelgYhdlg" }
    ]
}

Extended Rollbar Logging

In order to log all requests/responses prior to an exception reported by Rollbar in addition to the exception itself, use the DHS::ExtendedRollbar interceptor in combination with the rollbar processor/handler:

# config/initializers/dhc.rb

DHC.configure do |config|
  config.interceptors = [DHS::ExtendedRollbar]
end

# config/initializers/rollbar.rb

Rollbar.configure do |config|
  config.before_process << DHS::Interceptors::ExtendedRollbar::Handler.init
end

Testing with DHS

Best practice in regards of testing applications using DHS, is to let DHS fetch your records, actually perform HTTP requests and WebMock to stub/mock those http requests/responses.

This follows the Black Box Testing approach and prevents you from creating constraints to DHS' internal structures and mechanisms, which will break as soon as we change internals.

# specs/*/some_spec.rb 

let(:contracts) do
  [
    {number: '1'},
    {number: '2'},
    {number: '3'}
  ]
end

before do
  stub_request(:get, "https://service.example.com/contracts")
    .to_return(
      body: {
        items: contracts,
        limit: 10,
        total: contracts.length,
        offset: 0
      }.to_json
    )
end

it 'displays contracts' do
  visit 'contracts'
  contracts.each do |contract|
    expect(page).to have_content(contract[:number])
  end
end

Test helper

In order to load DHS test helpers into your tests, add the following to your spec helper:

# spec/spec_helper.rb

require 'dhs/rspec'

This e.g. will prevent running into caching issues during your tests, when (request cycle cache)[#request-cycle-cache] is enabled. It will initialize a MemoryStore cache for DHC::Caching interceptor and resets the cache before every test.

Stub

DHS offers stub helpers that simplify stubbing https request to your apis through your defined Records.

stub_all

Record.stub_all(url, items, additional_options)

# your_spec.rb

before do
  class Record < DHS::Record
    endpoint 'https://records'
  end

  Record.stub_all(
    'https://records',
    200.times.map{ |index| { name: "Item #{index}" } },
    headers: {
      'Authorization' => 'Bearer 123'
    }
  )
end

GET https://records?limit=100
GET https://records?limit=100&offset=100

DHS also uses Record configuration when stubbing all.

# your_spec.rb

before do
  class Record < DHS::Record
    configuration limit_key: :per_page, pagination_strategy: :page, pagination_key: :page

    endpoint 'https://records'
  end

  Record.stub_all(
    'https://records',
    200.times.map{ |index| { name: "Item #{index}" } }
  )
end

GET https://records?per_page=100
GET https://records?per_page=100&page=2

Test query chains

By explicitly resolving the chain: fetch

Use fetch in tests to resolve chains in place and expect WebMock stubs to be requested.

# specs/*/some_spec.rb 

records = Record.where(color: 'blue').where(available: true).where(color: 'red')

expect(
  records.fetch
).to have_requested(:get, %r{records/})
  .with(query: hash_including(color: 'blue', available: true))

Without resolving the chain: where_values_hash

As where chains are not resolving to HTTP-requests when no data is accessed, you can use where_values_hash to access the values that would be used to resolve the chain, and test those:

# specs/*/some_spec.rb 

records = Record.where(color: 'blue').where(available: true).where(color: 'red')

expect(
  records.where_values_hash
).to eq {color: 'red', available: true}

Extended developer documentation

Accessing data in DHS

License

GNU General Public License Version 3.