Alba
Alba is a JSON serializer for Ruby, JRuby, and TruffleRuby.
TL;DR
Alba allows you to do something like below.
class User
attr_accessor :id, :name, :email
def initialize(id, name, email)
@id = id
@name = name
@email = email
end
end
class UserResource
include Alba::Resource
root_key :user
attributes :id, :name
attribute :name_with_email do |resource|
"#{resource.name}: #{resource.email}"
end
end
user = User.new(1, 'Masafumi OKURA', '[email protected]')
UserResource.new(user).serialize
# => '{"user":{"id":1,"name":"Masafumi OKURA","name_with_email":"Masafumi OKURA: [email protected]"}}'
Seems useful? Continue reading!
Discussions
Alba uses GitHub Discussions to openly discuss the project.
If you've already used Alba, please consider posting your thoughts and feelings on Feedback. The fact that you enjoy using Alba gives me energy to keep developing Alba!
If you have feature requests or interesting ideas, join us with Ideas. Let's make Alba even better, together!
Resources
If you want to know more about Alba, there's a screencast created by Sebastian from Hanami Mastery. It covers basic features of Alba and how to use it in Hanami.
What users say about Alba
Alba is a well-maintained JSON serialization engine, for Ruby, JRuby, and TruffleRuby implementations, and what I like in this gem - except of its speed, is the easiness of use, no dependencies and the fact it plays well with any Ruby application!
Alba is more feature-rich and pretty fast, too
Gemfile of dreams by Evil Martians
Why Alba?
Because it's fast, easy and feature rich!
Fast
Alba is faster than most of the alternatives. We have a benchmark.
Easy
Alba is easy to use because there are only a few methods to remember. It's also easy to understand due to clean and small codebase. Finally it's easy to extend since it provides some methods for override to change default behavior of Alba.
Feature rich
While Alba's core is simple, it provides additional features when you need them, For example, Alba provides a way to control circular associations, root key and association resource name inference and supports layouts.
Other reasons
- Dependency free, no need to install
oj
oractivesupport
while Alba works well with them - Well tested, the test coverage is 99%
- Well maintained, gettings frequent update and new releases (see version history)
Installation
Add this line to your application's Gemfile:
gem 'alba'
And then execute:
$ bundle install
Or install it yourself as:
$ gem install alba
Supported Ruby versions
Alba supports CRuby 3.0 and higher and latest JRuby and TruffleRuby.
Documentation
You can find the documentation on RubyDoc.
Features
- Conditional attributes and associations
- Selectable backend
- Key transformation
- Root key and association resource name inference
- Error handling
- Nil handling
- Circular associations control
- Types for validation and conversion
- Layout
- No runtime dependencies
Usage
Configuration
Alba's configuration is fairly simple.
Backend configuration
Backend is the actual part serializing an object into JSON. Alba supports these backends.
name | description | requires_external_gem | encoder |
---|---|---|---|
oj , oj_strict |
Using Oj in strict mode |
Yes(C extension) | Oj.dump(object, mode: :strict) |
oj_rails |
It's oj but in rails mode |
Yes(C extension) | Oj.dump(object, mode: :rails) |
oj_default |
It's oj but respects mode set by users |
Yes(C extension) | Oj.dump(object) |
active_support |
For Rails compatibility | Yes | ActiveSupport::JSON.encode(object) |
default , json |
Using json gem |
No | JSON.generate(object) |
You can set a backend like this:
Alba.backend = :oj
This is equivalent as:
Alba.encoder = ->(object) { Oj.dump(object, mode: :strict) }
Encoder configuration
You can also set JSON encoder directly with a Proc.
Alba.encoder = ->(object) { JSON.generate(object) }
You can consider setting a backend with Symbol as a shortcut to set encoder.
Inference configuration
You can enable the inference feature using the Alba.inflector = SomeInflector
API. For example, in a Rails initializer:
Alba.inflector = :active_support
You can choose which inflector Alba uses for inference. Possible options are:
:active_support
forActiveSupport::Inflector
:dry
forDry::Inflector
- any object which conforms to the protocol (see below)
To disable inference, set the inflector
to nil
:
Alba.inflector = nil
To check if inference is enabled etc, inspect the return value of inflector
:
if Alba.inflector.nil?
puts 'inflector not set'
else
puts "inflector is set to #{Alba.inflector}"
end
Naming
Alba tries to infer resource name from class name like the following.
Class name | Resource name |
---|---|
FooResource | Foo |
FooSerializer | Foo |
FooElse | FooElse |
Resource name is used as the default name of the root key, so you might want to name it ending with "Resource" or "Serializer"
When you use Alba with Rails, it's recommended to put your resource/serializer classes in corresponding directory such as app/resources
or app/serializers
.
Simple serialization with root key
You can define attributes with (yes) attributes
macro with attribute names. If your attribute need some calculations, you can use attribute
with block.
class User
attr_accessor :id, :name, :email, :created_at, :updated_at
def initialize(id, name, email)
@id = id
@name = name
@email = email
@created_at = Time.now
@updated_at = Time.now
end
end
class UserResource
include Alba::Resource
root_key :user
attributes :id, :name
attribute :name_with_email do |resource|
"#{resource.name}: #{resource.email}"
end
end
user = User.new(1, 'Masafumi OKURA', '[email protected]')
UserResource.new(user).serialize
# => '{"user":{"id":1,"name":"Masafumi OKURA","name_with_email":"Masafumi OKURA: [email protected]"}}'
You can define instance methods on resources so that you can use it as attribute name in attributes
.
# The serialization result is the same as above
class UserResource
include Alba::Resource
root_key :user, :users # Later is for plural
attributes :id, :name, :name_with_email
# Attribute methods must accept one argument for each serialized object
def name_with_email(user)
"#{user.name}: #{user.email}"
end
end
This even works with users collection.
user1 = User.new(1, 'Masafumi OKURA', '[email protected]')
user2 = User.new(2, 'Test User', '[email protected]')
UserResource.new([user1, user2]).serialize
# => '{"users":[{"id":1,"name":"Masafumi OKURA","name_with_email":"Masafumi OKURA: [email protected]"},{"id":2,"name":"Test User","name_with_email":"Test User: [email protected]"}]}'
If you have a simple case where you want to change only the name, you can use the Symbol to Proc shortcut:
class UserResource
include Alba::Resource
attribute :some_other_name, &:name
end
Prefer methods on resource
By default, Alba prefers methods on the object to methods on the resource. This means if you have a following situation:
class User
attr_accessor :id, :name, :email
def initialize(id, name, email)
@id = id
@name = name
@email = email
end
def name_with_email
'dummy!'
end
end
class UserResource
include Alba::Resource
root_key :user, :users # Later is for plural
attributes :id, :name, :name_with_email
# Same method exists in `User` class!
# This is not called
def name_with_email(user)
"#{user.name}: #{user.email}"
end
end
user = User.new(1, 'Masafumi OKURA', '[email protected]')
UserResource.new(user).serialize
# => '{"user":{"id":1,"name":"Masafumi OKURA","name_with_email":"dummy!"}}'
You can see that name_with_email
is now dummy!
from User#name_with_email
. You cna change this behavior by using prefer_resource_method!
DSL in a resource class:
# With the same `User` class
class UserResource
include Alba::Resource
prefer_resource_method! # This line is important
root_key :user, :users # Later is for plural
attributes :id, :name, :name_with_email
# Same method exists in `User` class!
# But now this is called!
def name_with_email(user)
"#{user.name}: #{user.email}"
end
end
user = User.new(1, 'Masafumi OKURA', '[email protected]')
UserResource.new(user).serialize
# => '{"user":{"id":1,"name":"Masafumi OKURA","name_with_email":"Masafumi OKURA: [email protected]"}}'
The next major version of Alba will change this default behavior to prefer resource methods. In case you want to preserve current behavior, there's prefer_object_method!
DSL, which does that.
Params
You can pass a Hash to the resource for internal use. It can be used as "flags" to control attribute content.
class UserResource
include Alba::Resource
attribute :name do |user|
params[:upcase] ? user.name.upcase : user.name
end
end
user = User.new(1, 'Masa', '[email protected]')
UserResource.new(user).serialize # => '{"name":"Masa"}'
UserResource.new(user, params: {upcase: true}).serialize # => '{"name":"MASA"}'
Serialization with associations
Associations can be defined using the association
macro, which is also aliased as one
, many
, has_one
, and has_many
for convenience.
class User
attr_reader :id, :created_at, :updated_at
attr_accessor :articles
def initialize(id)
@id = id
@created_at = Time.now
@updated_at = Time.now
@articles = []
end
end
class Article
attr_accessor :user_id, :title, :body
def initialize(user_id, title, body)
@user_id = user_id
@title = title
@body = body
end
end
class ArticleResource
include Alba::Resource
attributes :title
end
class UserResource
include Alba::Resource
attributes :id
many :articles, resource: ArticleResource
end
user = User.new(1)
article1 = Article.new(1, 'Hello World!', 'Hello World!!!')
user.articles << article1
article2 = Article.new(2, 'Super nice', 'Really nice!')
user.articles << article2
UserResource.new(user).serialize
# => '{"id":1,"articles":[{"title":"Hello World!"},{"title":"Super nice"}]}'
You can define associations inline if you don't need a class for association.
class ArticleResource
include Alba::Resource
attributes :title
end
class UserResource
include Alba::Resource
attributes :id
many :articles, resource: ArticleResource
end
# This class works the same as `UserResource`
class AnotherUserResource
include Alba::Resource
attributes :id
many :articles do
attributes :title
end
end
You can "filter" association using second proc argument. This proc takes association object, params
and initial object.
This feature is useful when you want to modify association, such as adding includes
or order
to ActiveRecord relations.
class User
attr_reader :id, :banned
attr_accessor :articles
def initialize(id, banned = false)
@id = id
@banned = banned
@articles = []
end
end
class Article
attr_accessor :id, :title, :body
def initialize(id, title, body)
@id = id
@title = title
@body = body
end
end
class ArticleResource
include Alba::Resource
attributes :title
end
class UserResource
include Alba::Resource
attributes :id
# Second proc works as a filter
many :articles,
proc { |articles, params, user|
filter = params[:filter] || :odd?
articles.select { |a| a.id.__send__(filter) && !user.banned }
},
resource: ArticleResource
end
user = User.new(1)
article1 = Article.new(1, 'Hello World!', 'Hello World!!!')
user.articles << article1
article2 = Article.new(2, 'Super nice', 'Really nice!')
user.articles << article2
UserResource.new(user).serialize
# => '{"id":1,"articles":[{"title":"Hello World!"}]}'
UserResource.new(user, params: {filter: :even?}).serialize
# => '{"id":1,"articles":[{"title":"Super nice"}]}'
You can change a key for association with key
option.
class UserResource
include Alba::Resource
attributes :id
many :articles,
key: 'my_articles', # Set key here
resource: ArticleResource
end
UserResource.new(user).serialize
# => '{"id":1,"my_articles":[{"title":"Hello World!"}]}'
You can omit the resource option if you enable Alba's inference feature.
Alba.inflector = :active_support
class UserResource
include Alba::Resource
attributes :id
many :articles # Using `ArticleResource`
end
UserResource.new(user).serialize
# => '{"id":1,"my_articles":[{"title":"Hello World!"}]}'
If you need complex logic to determine what resource to use for association, you can use a Proc for resource option.
class UserResource
include Alba::Resource
attributes :id
many :articles, resource: ->(article) { article.with_comment? ? ArticleWithCommentResource : ArticleResource }
end
Note that using a Proc slows down serialization if there are too many
associated objects.
Params override
Associations can override params. This is useful when associations are deeply nested.
class BazResource
include Alba::Resource
attributes :data
attributes :secret, if: proc { params[:expose_secret] }
end
class BarResource
include Alba::Resource
one :baz, resource: BazResource
end
class FooResource
include Alba::Resource
root_key :foo
one :bar, resource: BarResource
end
class FooResourceWithParamsOverride
include Alba::Resource
root_key :foo
one :bar, resource: BarResource, params: {expose_secret: false}
end
Baz = Struct.new(:data, :secret)
Bar = Struct.new(:baz)
Foo = Struct.new(:bar)
foo = Foo.new(Bar.new(Baz.new(1, 'secret')))
FooResource.new(foo, params: {expose_secret: true}).serialize # => '{"foo":{"bar":{"baz":{"data":1,"secret":"secret"}}}}'
FooResourceWithParamsOverride.new(foo, params: {expose_secret: true}).serialize # => '{"foo":{"bar":{"baz":{"data":1}}}}'
Nested Attribute
Alba supports nested attributes that makes it easy to build complex data structure from single object.
In order to define nested attributes, you can use nested
or nested_attribute
(alias of nested
).
class User
attr_accessor :id, :name, :email, :city, :zipcode
def initialize(id, name, email, city, zipcode)
@id = id
@name = name
@email = email
@city = city
@zipcode = zipcode
end
end
class UserResource
include Alba::Resource
root_key :user
attributes :id
nested_attribute :address do
attributes :city, :zipcode
end
end
user = User.new(1, 'Masafumi OKURA', '[email protected]', 'Tokyo', '0000000')
UserResource.new(user).serialize
# => '{"user":{"id":1,"address":{"city":"Tokyo","zipcode":"0000000"}}}'
Nested attributes can be nested deeply.
class FooResource
include Alba::Resource
root_key :foo
nested :bar do
nested :baz do
attribute :deep do
42
end
end
end
end
FooResource.new(nil).serialize
# => '{"foo":{"bar":{"baz":{"deep":42}}}}'
Inline definition with Alba.serialize
Alba.serialize
method is a shortcut to define everything inline.
Alba.serialize(user, root_key: :foo) do
attributes :id
many :articles do
attributes :title, :body
end
end
# => '{"foo":{"id":1,"articles":[{"title":"Hello World!","body":"Hello World!!!"},{"title":"Super nice","body":"Really nice!"}]}}'
Alba.serialize
can be used when you don't know what kind of object you serialize. For example:
Alba.serialize(something)
# => Same as `FooResource.new(something).serialize` when `something` is an instance of `Foo`.
Although this might be useful sometimes, it's generally recommended to define a class for Resource.
Inline definition for multiple root keys
While Alba doesn't directly support multiple root keys, you can simulate it with Alba.serialize
.
# Define foo and bar local variables here
Alba.serialize do
attribute :key1 do
FooResource.new(foo).to_h
end
attribute :key2 do
BarResource.new().to_h
end
end
# => JSON containing "key1" and "key2" as root keys
Note that we must use to_h
, not serialize
, with resources.
We can also generate a JSON with multiple root keys without making any class by the combination of Alba.serialize
and Alba.hashify
.
# Define foo and bar local variables here
Alba.serialize do
attribute :foo do
Alba.hashify(foo) do
attributes :id, :name # For example
end
end
attribute :bar do
Alba.hashify() do
attributes :id
end
end
end
# => JSON containing "foo" and "bar" as root keys
Serializable Hash
Instead of serializing to JSON, you can also output a Hash by calling serializable_hash
or the to_h
alias. Note also that the serialize
method is aliased as to_json
.
# These are equivalent and will return serialized JSON
UserResource.new(user).serialize
UserResource.new(user).to_json
# These are equivalent and will return a Hash
UserResource.new(user).serializable_hash
UserResource.new(user).to_h
If you want a Hash that corresponds to a JSON String returned by serialize
method, you can use as_json
.
# These are equivalent and will return the same result
UserResource.new(user).serialize
UserResource.new(user).to_json
JSON.generate(UserResource.new(user).as_json)
Inheritance
When you include Alba::Resource
in your class, it's just a class so you can define any class that inherits from it. You can add new attributes to inherited class like below:
class FooResource
include Alba::Resource
root_key :foo
attributes :bar
end
class ExtendedFooResource < FooResource
root_key :foofoo
attributes :baz
end
Foo = Struct.new(:bar, :baz)
foo = Foo.new(1, 2)
FooResource.new(foo).serialize # => '{"foo":{"bar":1}}'
ExtendedFooResource.new(foo).serialize # => '{"foofoo":{"bar":1,"baz":2}}'
In this example we add baz
attribute and change root_key
. This way, you can extend existing resource classes just like normal OOP. Don't forget that when your inheritance structure is too deep it'll become difficult to modify existing classes.
Filtering attributes
Filtering attributes can be done in two ways - with attributes
and select
. They have different semantics and usage.
select
is a new and more intuitive API, so generally it's recommended to use select
.
Filtering attributes with attributes
You can filter out certain attributes by overriding attributes
instance method. This is useful when you want to customize existing resource with inheritance.
You can access raw attributes via super
call. It returns a Hash whose keys are the name of the attribute and whose values are the body. Usually you need only keys to filter out, like below.
class Foo
attr_accessor :id, :name, :body
def initialize(id, name, body)
@id = id
@name = name
@body = body
end
end
class GenericFooResource
include Alba::Resource
attributes :id, :name, :body
end
class RestrictedFooResource < GenericFooResource
def attributes
super.select { |key, _| key.to_sym == :name }
end
end
foo = Foo.new(1, 'my foo', 'body')
RestrictedFooResource.new(foo).serialize
# => '{"name":"my foo"}'
Filtering attributes with select
When you want to filter attributes based on more complex logic, you can use select
instance method. select
takes two parameters, the name of an attribute and the value of an attribute. If it returns false that attribute is rejected.
class Foo
attr_accessor :id, :name, :body
def initialize(id, name, body)
@id = id
@name = name
@body = body
end
end
class GenericFooResource
include Alba::Resource
attributes :id, :name, :body
end
class RestrictedFooResource < GenericFooResource
def select(_key, value)
!value.nil?
end
end
foo = Foo.new(1, nil, 'body')
RestrictedFooResource.new(foo).serialize
# => '{"id":1,"body":"body"}'
Key transformation
If you have inference enabled, you can use the transform_keys
DSL to transform attribute keys.
Alba.inflector = :active_support
class User
attr_reader :id, :first_name, :last_name
def initialize(id, first_name, last_name)
@id = id
@first_name = first_name
@last_name = last_name
end
end
class UserResource
include Alba::Resource
attributes :id, :first_name, :last_name
transform_keys :lower_camel
end
user = User.new(1, 'Masafumi', 'Okura')
UserResourceCamel.new(user).serialize
# => '{"id":1,"firstName":"Masafumi","lastName":"Okura"}'
Possible values for transform_keys
argument are:
:camel
for CamelCase:lower_camel
for lowerCamelCase:dash
for dash-case:snake
for snake_case:none
for not transforming keys
Root key transformation
You can also transform root key when:
Alba.inflector
is setroot_key!
is called in Resource classroot
option oftransform_keys
is set to true
Alba.inflector = :active_support
class BankAccount
attr_reader :account_number
def initialize(account_number)
@account_number = account_number
end
end
class BankAccountResource
include Alba::Resource
root_key!
attributes :account_number
transform_keys :dash, root: true
end
bank_account = BankAccount.new(123_456_789)
BankAccountResource.new(bank_account).serialize
# => '{"bank-account":{"account-number":123456789}}'
This is the default behavior from version 2.
Find more details in the Inference configuration section.
Key transformation cascading
When you use transform_keys
with inline association, it automatically applies the same transformation type to those inline association.
This is the default behavior from version 2, but you can do the same thing with adding transform_keys
to each association.
You can also turn it off by setting cascade: false
option to transform_keys
.
class User
attr_reader :id, :first_name, :last_name, :bank_account
def initialize(id, first_name, last_name)
@id = id
@first_name = first_name
@last_name = last_name
@bank_account = BankAccount.new(1234)
end
end
class BankAccount
attr_reader :account_number
def initialize(account_number)
@account_number = account_number
end
end
class UserResource
include Alba::Resource
attributes :id, :first_name, :last_name
transform_keys :lower_camel # Default is cascade: true
one :bank_account do
attributes :account_number
end
end
user = User.new(1, 'Masafumi', 'Okura')
UserResource.new(user).serialize
# => '{"id":1,"firstName":"Masafumi","lastName":"Okura","bankAccount":{"accountNumber":1234}}'
Custom inflector
A custom inflector can be plugged in as follows.
module CustomInflector
module_function
def camelize(string); end
def camelize_lower(string); end
def dasherize(string); end
def underscore(string); end
def classify(string); end
end
Alba.inflector = CustomInflector
Conditional attributes
Filtering attributes with overriding attributes
works well for simple cases. However, It's cumbersome when we want to filter various attributes based on different conditions for keys.
In these cases, conditional attributes works well. We can pass if
option to attributes
, attribute
, one
and many
. Below is an example for the same effect as filtering attributes section.
class User
attr_accessor :id, :name, :email
def initialize(id, name, email)
@id = id
@name = name
@email = email
end
end
class UserResource
include Alba::Resource
attributes :id, :name, :email, if: proc { |user, attribute| !attribute.nil? }
end
user = User.new(1, nil, nil)
UserResource.new(user).serialize # => '{"id":1}'
Default
Alba doesn't support default value for attributes, but it's easy to set a default value.
class FooResource
attribute :bar do |foo|
foo. || 'default bar'
end
end
We believe this is clearer than using some (not implemented yet) DSL such as default
because there are some conditions where default values should be applied (nil
, blank?
, empty?
etc.)
Root key and association resource name inference
If inference is enabled, Alba tries to infer the root key and association resource names.
Alba.inflector = :active_support
class User
attr_reader :id
attr_accessor :articles
def initialize(id)
@id = id
@articles = []
end
end
class Article
attr_accessor :id, :title
def initialize(id, title)
@id = id
@title = title
end
end
class ArticleResource
include Alba::Resource
attributes :title
end
class UserResource
include Alba::Resource
root_key!
attributes :id
many :articles
end
user = User.new(1)
user.articles << Article.new(1, 'The title')
UserResource.new(user).serialize # => '{"user":{"id":1,"articles":[{"title":"The title"}]}}'
UserResource.new([user]).serialize # => '{"users":[{"id":1,"articles":[{"title":"The title"}]}]}'
This resource automatically sets its root key to either "users" or "user", depending on the given object is collection or not.
Also, you don't have to specify which resource class to use with many
. Alba infers it from association name.
Find more details in the Inference configuration section.
Error handling
You can set error handler globally or per resource using on_error
.
class User
attr_accessor :id, :name
def initialize(id, name, email)
@id = id
@name = name
@email = email
end
def email
raise 'Error!'
end
end
class UserResource
include Alba::Resource
attributes :id, :name, :email
on_error :ignore
end
user = User.new(1, 'Test', '[email protected]')
UserResource.new(user).serialize # => '{"id":1,"name":"Test"}'
This way you can exclude an entry when fetching an attribute gives an exception.
There are four possible arguments on_error
method accepts.
:raise
re-raises an error. This is the default behavior.:ignore
ignores the entry with the error.:nullify
sets the attribute with the error tonil
.- Block gives you more control over what to be returned.
The block receives five arguments, error
, object
, key
, attribute
and resource class
and must return a two-element array. Below is an example.
class ExampleResource
include Alba::Resource
on_error do |error, object, key, attribute, resource_class|
if resource_class == MyResource
['error_fallback', object.error_fallback]
else
[key, error.]
end
end
end
Nil handling
Sometimes we want to convert nil
to different values such as empty string. Alba provides a flexible way to handle nil
.
class User
attr_reader :id, :name, :age
def initialize(id, name = nil, age = nil)
@id = id
@name = name
@age = age
end
end
class UserResource
include Alba::Resource
on_nil { '' }
root_key :user, :users
attributes :id, :name, :age
end
UserResource.new(User.new(1)).serialize
# => '{"user":{"id":1,"name":"","age":""}}'
You can get various information via block parameters.
class UserResource
include Alba::Resource
on_nil do |object, key|
if key == 'age'
20
else
"User#{object.id}"
end
end
root_key :user, :users
attributes :id, :name, :age
end
UserResource.new(User.new(1)).serialize
# => '{"user":{"id":1,"name":"User1","age":20}}'
Note that on_nil
does NOT work when the given object itself is nil
. There are a few possible ways to deal with nil
.
- Use
if
statement and avoid using Alba when the object isnil
- Use "Null Object" pattern
Metadata
You can set a metadata with meta
DSL or meta
option.
class UserResource
include Alba::Resource
root_key :user, :users
attributes :id, :name
do
if object.is_a?(Enumerable)
{size: object.size}
else
{foo: :bar}
end
end
end
user = User.new(1, 'Masafumi OKURA', '[email protected]')
UserResource.new([user]).serialize
# => '{"users":[{"id":1,"name":"Masafumi OKURA"}],"meta":{"size":1}}'
# You can merge metadata with `meta` option
UserResource.new([user]).serialize(meta: {foo: :bar})
# => '{"users":[{"id":1,"name":"Masafumi OKURA"}],"meta":{"size":1,"foo":"bar"}}'
# You can set metadata with `meta` option alone
class UserResourceWithoutMeta
include Alba::Resource
root_key :user, :users
attributes :id, :name
end
UserResourceWithoutMeta.new([user]).serialize(meta: {foo: :bar})
# => '{"users":[{"id":1,"name":"Masafumi OKURA"}],"meta":{"foo":"bar"}}'
You can use object
method to access the underlying object and params
to access the params in meta
block.
Note that setting root key is required when setting a metadata.
Circular associations control
Note that this feature works correctly since version 1.3. In previous versions it doesn't work as expected.
You can control circular associations with within
option. within
option is a nested Hash such as {book: {authors: books}}
. In this example, Alba serializes a book's authors' books. This means you can reference BookResource
from AuthorResource
and vice versa. This is really powerful when you have a complex data structure and serialize certain parts of it.
For more details, please refer to test code
Experimental support of types
You can validate and convert input with types.
class User
attr_reader :id, :name, :age, :bio, :admin, :created_at
def initialize(id, name, age, bio = '', admin = false)
@id = id
@name = name
@age = age
@admin = admin
@bio = bio
@created_at = Time.new(2020, 10, 10)
end
end
class UserResource
include Alba::Resource
attributes :name, id: [String, true], age: [Integer, true], bio: String, admin: [:Boolean, true], created_at: [String, ->(object) { object.strftime('%F') }]
end
user = User.new(1, 'Masafumi OKURA', '32', 'Ruby dev')
UserResource.new(user).serialize
# => '{"name":"Masafumi OKURA","id":"1","age":32,"bio":"Ruby dev","admin":false,"created_at":"2020-10-10"}'
Notice that id
and created_at
are converted to String and age
is converted to Integer.
If type is not correct and auto conversion is disabled (default), TypeError
occurs.
user = User.new(1, 'Masafumi OKURA', '32', nil) # bio is nil and auto conversion is disabled for bio
UserResource.new(user).serialize
# => TypeError, 'Attribute bio is expected to be String but actually nil.'
Note that this feature is experimental and interfaces are subject to change.
Collection serialization into Hash
Sometimes we want to serialize a collection into a Hash, not an Array. It's possible with Alba.
class User
attr_reader :id, :name
def initialize(id, name)
@id = id
@name = name
end
end
class UserResource
include Alba::Resource
collection_key :id # This line is important
attributes :id, :name
end
user1 = User.new(1, 'John')
user2 = User.new(2, 'Masafumi')
UserResource.new([user1, user2]).serialize
# => '{"1":{"id":1,"name":"John"},"2":{"id":2,"name":"Masafumi"}}'
In the snippet above, collection_key :id
specifies the key used for the key of the collection hash. In this example it's :id
.
Make sure that collection key is unique for the collection.
Layout
Sometimes we'd like to serialize JSON into a template. In other words, we need some structure OUTSIDE OF serialized JSON. IN HTML world, we call it a "layout".
Alba supports serializing JSON in a layout. You need a file for layout and then to specify file with layout
method.
{
"header": "my_header",
"body": <%= serialized_json %>
}
class FooResource
include Alba::Resource
layout file: 'my_layout.json.erb'
end
Note that layout files are treated as json
and erb
and evaluated in a context of the resource, meaning
- A layout file must be a valid JSON
- You must write
<%= serialized_json %>
in a layout to put serialized JSON string into a layout - You can access
params
in a layout so that you can add virtually any objects to a layout- When you access
params
, it's usually a Hash. You can useencode
method in a layout to convertparams
Hash into a JSON with the backend you use
- When you access
- You can also access
object
, the underlying object for the resource
In case you don't want to have a file for layout, Alba lets you define and apply layouts inline:
class FooResource
include Alba::Resource
layout inline: proc {
{
header: 'my header',
body: serializable_hash
}
}
end
In the example above, we specify a Proc which returns a Hash as an inline layout. In the Proc we can use serializable_hash
method to access a Hash right before serialization.
You can also use a Proc which returns String, not a Hash, for an inline layout.
class FooResource
include Alba::Resource
layout inline: proc {
%({
"header": "my header",
"body": #{serialized_json}
})
}
end
It looks similar to file layout but you must use string interpolation for method calls since it's not an ERB.
Also note that we use percentage notation here to use double quotes. Using single quotes in inline string layout causes the error which might be resolved in other ways.
Helper
Inheritance works well in most of the cases to share behaviors. One of the exceptions is when you want to shared behaviors with inline association. For example:
class ApplicationResource
include Alba::Resource
def self.with_id
attributes(:id)
end
end
class LibraryResource < ApplicationResource
with_id
attributes :created_at
with_many :library_books do
with_id # This DOES NOT work!
attributes :created_at
end
end
This doesn't work. Technically, inside of has_many
is a separate class which doesn't inherit from the base class (LibraryResource
in this example).
helper
solves this problem. It's just a mark for methods that should be shared with inline associations.
class ApplicationResource
include Alba::Resource
helper do
def with_id
attributes(:id)
end
end
end
# Now `LibraryResource` works!
Within helper
block, all methods should be defined without self.
.
Caching
Currently, Alba doesn't support caching, primarily due to the behavior of ActiveRecord::Relation
's cache. See the issue.
Extend Alba
Sometimes we have shared behaviors across resources. In such cases we can have a module for common logic.
In attribute
block we can call instance method so we can improve the code below:
class FooResource
include Alba::Resource
# other attributes
attribute :created_at do |foo|
foo.created_at.strftime('%m/%d/%Y')
end
attribute :updated_at do |foo|
foo.updated_at.strftime('%m/%d/%Y')
end
end
class BarResource
include Alba::Resource
# other attributes
attribute :created_at do ||
.created_at.strftime('%m/%d/%Y')
end
attribute :updated_at do ||
.updated_at.strftime('%m/%d/%Y')
end
end
to:
module SharedLogic
def format_time(time)
time.strftime('%m/%d/%Y')
end
end
class FooResource
include Alba::Resource
include SharedLogic
# other attributes
attribute :created_at do |foo|
format_time(foo.created_at)
end
attribute :updated_at do |foo|
format_time(foo.updated_at)
end
end
class BarResource
include Alba::Resource
include SharedLogic
# other attributes
attribute :created_at do ||
format_time(.created_at)
end
attribute :updated_at do ||
format_time(.updated_at)
end
end
We can even add our own DSL to serialize attributes for readability and removing code duplications.
To do so, we need to extend
our module. Let's see how we can achieve the same goal with this approach.
module AlbaExtension
# Here attrs are an Array of Symbol
def formatted_time_attributes(*attrs)
attrs.each do |attr|
attribute(attr) do |object|
time = object.__send__(attr)
time.strftime('%m/%d/%Y')
end
end
end
end
class FooResource
include Alba::Resource
extend AlbaExtension
# other attributes
formatted_time_attributes :created_at, :updated_at
end
class BarResource
include Alba::Resource
extend AlbaExtension
# other attributes
formatted_time_attributes :created_at, :updated_at
end
In this way we have shorter and cleaner code. Note that we need to use send
or public_send
in attribute
block to get attribute data.
Debugging
Debugging is not easy. If you find Alba not working as you expect, there are a few things to do:
- Inspect
The typical code looks like this:
class FooResource
include Alba::Resource
attributes :id
end
FooResource.new(foo).serialize
Notice that we instantiate FooResource
and then call serialize
method. We can get various information by calling inspect
method on it.
puts FooResource.new(foo).inspect # or: p class FooResource.new(foo)
# => "#<FooResource:0x000000010e21f408 @object=[#<Foo:0x000000010e3470d8 @id=1>], @params={}, @within=#<Object:0x000000010df2eac8>, @method_existence={}, @_attributes={:id=>:id}, @_key=nil, @_key_for_collection=nil, @_meta=nil, @_transform_type=:none, @_transforming_root_key=false, @_on_error=nil, @_on_nil=nil, @_layout=nil, @_collection_key=nil>"
The output might be different depending on the version of Alba or the object you give, but the concepts are the same. @object
represents the object you gave as an argument to new
method, @_attributes
represents the attributes you defined in FooResource
class using attributes
DSL.
Other things are not so important, but you need to take care of corresponding part when you use additional features such as root_key
, transform_keys
and adding params.
- Logging
Alba currently doesn't support logging directly, but you can add your own logging module to Alba easily.
module Logging
# `...` was added in Ruby 2.7
def serialize(...)
puts serializable_hash
super(...)
end
end
FooResource.prepend(Logging)
FooResource.new(foo).serialize
# => "{:id=>1}" is printed
Here, we override serialize
method with prepend
. In overridden method we print the result of serializable_hash
that gives the basic hash for serialization to serialize
method. Using ...
allows us to override without knowing method signiture of serialize
.
Don't forget calling super
in this way.
Rails
When you use Alba in Rails, you can create an initializer file with the line below for compatibility with Rails JSON encoder.
Alba.backend = :active_support
# or
Alba.backend = :oj_rails
To find out more details, please see https://github.com/okuramasafumi/alba/blob/main/docs/rails.md
Why named "Alba"?
The name "Alba" comes from "albatross", a kind of birds. In Japanese, this bird is called "Aho-dori", which means "stupid bird". I find it funny because in fact albatrosses fly really fast. I hope Alba looks stupid but in fact it does its job quick.
Pioneers
There are great pioneers in Ruby's ecosystem which does basically the same thing as Alba does. To name a few:
- ActiveModelSerializers a.k.a AMS, the most famous implementation of JSON serializer for Ruby
- Blueprinter shares some concepts with Alba
Development
After checking out the repo, run bin/setup
to install dependencies. Then, run bundle exec rake test
to run the tests. You can also run bin/console
for an interactive prompt that will allow you to experiment.
To install this gem onto your local machine, run bundle exec rake install
. To release a new version, update the version number in version.rb
, and then run bundle exec rake release
, which will create a git tag for the version, push git commits and tags, and push the .gem
file to rubygems.org.
Contributing
Thank you for begin interested in contributing to Alba! Please see contributors guide before start contributing. If you have any questions, please feel free to ask in Discussions.
License
The gem is available as open source under the terms of the MIT License.
Code of Conduct
Everyone interacting in the Alba project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.