Class: ViewModel

Inherits:
Object
  • Object
show all
Defined in:
lib/view_model.rb,
lib/view_model/migrator.rb,
lib/view_model/reference.rb,
lib/view_model/references.rb,
lib/view_model/deserialization_error.rb

Defined Under Namespace

Modules: AfterTransactionRunner, Callbacks, Controller, MigratableView, TestHelpers Classes: AbstractError, AbstractErrorCollection, AbstractErrorWithBlame, AccessControl, AccessControlError, ActiveRecord, Changes, Config, DeserializationError, DeserializeContext, DownMigrator, Error, ErrorView, GarbageCollection, Metadata, Migration, Migrator, Record, Reference, References, Registry, Schemas, SerializationError, SerializeContext, TraversalContext, UpMigrator, Utils, WrappedExceptionError

Constant Summary collapse

REFERENCE_ATTRIBUTE = 
'_ref'
ID_ATTRIBUTE = 
'id'
TYPE_ATTRIBUTE = 
'_type'
VERSION_ATTRIBUTE = 
'_version'
NEW_ATTRIBUTE =

The optional _new attribute specifies explicitly whether a deserialization is to an new or existing model. The behaviour of _new is as follows:

* true  - Always create a new model, using the id if provided, error if
          a model with that id already exists
* false - Never create a new model. If id isn’t provided, it's an error
          unless the viewmodel is being deserialized in the context of a
          singular association, in which case it's implicitly referring
          to the current child of that association, and is an error if
          that child doesn't exist.

  • nil - Create a new model if ‘id` is not specified, otherwise update the

    existing record with `id`, and error if it doesn't exist.

  • ‘auto’ - Can only be used when the viewmodel is being deserialized in the

    context of a singular association. `id` must not be specified. If
the association currently has a child, update it, otherwise
create a new one.

'_new'
BULK_UPDATE_TYPE = 
'_bulk_update'
BULK_UPDATES_ATTRIBUTE = 
'updates'
BULK_UPDATE_ATTRIBUTE = 
'update'
MIGRATED_ATTRIBUTE =

Migrations leave a metadata attribute _migrated on any views that they alter. This attribute is accessible as metadata when deserializing migrated input, and is included in the output serialization sent to clients.

'_migrated'

Class Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(*args) ⇒ ViewModel

Returns a new instance of ViewModel.



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# File 'lib/view_model.rb', line 339

def initialize(*args)
  self.class._attributes.each_with_index do |attr, idx|
    self.public_send(:"#{attr}=", args[idx])
  end
end

Class Attribute Details

._attributes ⇒ Object

Returns the value of attribute _attributes.



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# File 'lib/view_model.rb', line 72

def _attributes
  @_attributes
end

.schema_version ⇒ Object

Returns the value of attribute schema_version.



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# File 'lib/view_model.rb', line 73

def schema_version
  @schema_version
end

.synthetic ⇒ Object

Boolean to indicate if the viewmodel is synthetic. Synthetic viewmodels are nearly-invisible glue. They’re full viewmodels, but do not participate in hooks or registration. For example, a join table connecting A and B through T has a synthetic viewmodel T to represent the join model, but the external interface is a relationship of A to a list of Bs.



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# File 'lib/view_model.rb', line 83

def synthetic
  @synthetic
end

.view_aliases ⇒ Object (readonly)

Returns the value of attribute view_aliases.



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# File 'lib/view_model.rb', line 74

def view_aliases
  @view_aliases
end

.view_name ⇒ Object 



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# File 'lib/view_model.rb', line 96

def view_name
  @view_name ||=
    begin
      # try to auto-detect based on class name
      match = /(.*)View$/.match(self.name)
      raise ArgumentError.new("Could not auto-determine ViewModel name from class name '#{self.name}'") if match.nil?

      ViewModel::Registry.default_view_name(match[1])
    end
end

Class Method Details

.accepts_schema_version?(schema_version) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/view_model.rb', line 313

def accepts_schema_version?(schema_version)
  schema_version == self.schema_version
end

.add_view_alias(as) ⇒ Object 



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# File 'lib/view_model.rb', line 107

def add_view_alias(as)
  view_aliases << as
  ViewModel::Registry.register(self, as: as)
end

.attribute(attr, **_args) ⇒ Object 



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# File 'lib/view_model.rb', line 131

def attribute(attr, **_args)
  unless attr.is_a?(Symbol)
    raise ArgumentError.new('ViewModel attributes must be symbols')
  end

  attr_accessor attr

  define_method("deserialize_#{attr}") do |value, references: {}, deserialize_context: self.class.new_deserialize_context|
    self.public_send("#{attr}=", value)
  end
  _attributes << attr
end

.attributes(*attrs, **args) ⇒ Object

ViewModels are typically going to be pretty simple structures. Make it a bit easier to define them: attributes specified this way are given accessors and assigned in order by the default constructor.



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# File 'lib/view_model.rb', line 127

def attributes(*attrs, **args)
  attrs.each { |attr| attribute(attr, **args) }
end

.deserialize_context_class ⇒ Object 



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# File 'lib/view_model.rb', line 305

def deserialize_context_class
  ViewModel::DeserializeContext
end

.deserialize_from_view(hash_data, references: {}, deserialize_context: new_deserialize_context) ⇒ Object

Rebuild this viewmodel from a serialized hash.



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# File 'lib/view_model.rb', line 259

def deserialize_from_view(hash_data, references: {}, deserialize_context: new_deserialize_context)
  viewmodel = self.new
  deserialize_members_from_view(viewmodel, hash_data, references: references, deserialize_context: deserialize_context)
  viewmodel
end

.deserialize_members_from_view(viewmodel, view_hash, references:, deserialize_context:) ⇒ Object 



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# File 'lib/view_model.rb', line 265

def deserialize_members_from_view(viewmodel, view_hash, references:, deserialize_context:)
  ViewModel::Callbacks.wrap_deserialize(viewmodel, deserialize_context: deserialize_context) do |hook_control|
    if (bad_attrs = view_hash.keys - member_names).present?
      causes = bad_attrs.map do |bad_attr|
        ViewModel::DeserializationError::UnknownAttribute.new(bad_attr, viewmodel.blame_reference)
      end
      raise ViewModel::DeserializationError::Collection.for_errors(causes)
    end

    member_names.each do |attr|
      next unless view_hash.has_key?(attr)

      viewmodel.public_send("deserialize_#{attr}",
                            view_hash[attr],
                            references: references,
                            deserialize_context: deserialize_context)
    end

    deserialize_context.run_callback(ViewModel::Callbacks::Hook::BeforeValidate, viewmodel)
    viewmodel.validate!

    # More complex viewmodels can use this hook to track changes to
    # persistent backing models, and record the results. Primitive
    # viewmodels record no changes.
    if block_given?
      yield(hook_control)
    else
      hook_control.record_changes(Changes.new)
    end
  end
end

.eager_includes(include_referenced: true) ⇒ Object

If this viewmodel represents an AR model, what associations does it make use of? Returns a includes spec appropriate for DeepPreloader, either as AR-style nested hashes or DeepPreloader::Spec.



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# File 'lib/view_model.rb', line 197

def eager_includes(include_referenced: true)
  {}
end

.encode_json(value) ⇒ Object 



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# File 'lib/view_model.rb', line 247

def encode_json(value)
  # Jbuilder#encode no longer uses MultiJson, but instead calls `.to_json`. In
  # the context of ActiveSupport, we don't want this, because AS replaces the
  # .to_json interface with its own .as_json, which demands that everything is
  # reduced to a Hash before it can be JSON encoded. Using this is not only
  # slightly more expensive in terms of allocations, but also defeats the
  # purpose of our precompiled `CompiledJson` terminals. Instead serialize
  # using OJ with options equivalent to those used by MultiJson.
  Oj.dump(value, mode: :compat, time_format: :ruby, use_to_json: true)
end

.extract_reference_metadata(hash) ⇒ Object 



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# File 'lib/view_model.rb', line 183

def extract_reference_metadata(hash)
  ViewModel::Schemas.verify_schema!(ViewModel::Schemas::VIEWMODEL_REFERENCE, hash)
  hash.delete(ViewModel::REFERENCE_ATTRIBUTE)
end

.extract_reference_only_metadata(hash) ⇒ Object 



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# File 'lib/view_model.rb', line 175

def extract_reference_only_metadata(hash)
  ViewModel::Schemas.verify_schema!(ViewModel::Schemas::VIEWMODEL_UPDATE, hash)
  id             = hash.delete(ViewModel::ID_ATTRIBUTE)
  type_name      = hash.delete(ViewModel::TYPE_ATTRIBUTE)

  Metadata.new(id, type_name, nil, false, false)
end

.extract_viewmodel_metadata(hash) ⇒ Object

In deserialization, verify and extract metadata from a provided hash.



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# File 'lib/view_model.rb', line 159

def extract_viewmodel_metadata(hash)
  ViewModel::Schemas.verify_schema!(ViewModel::Schemas::VIEWMODEL_UPDATE, hash)
  id             = hash.delete(ViewModel::ID_ATTRIBUTE)
  type_name      = hash.delete(ViewModel::TYPE_ATTRIBUTE)
  schema_version = hash.delete(ViewModel::VERSION_ATTRIBUTE)
  new            = hash.delete(ViewModel::NEW_ATTRIBUTE)
  migrated       = hash.delete(ViewModel::MIGRATED_ATTRIBUTE) { false }

  if id && new == 'auto'
    raise ViewModel::DeserializationError::InvalidSyntax.new(
            "An explicit id must not be specified with an 'auto' child update")
  end

  Metadata.new(id, type_name, schema_version, new, migrated)
end

.inherited(subclass) ⇒ Object 



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# File 'lib/view_model.rb', line 85

def inherited(subclass)
  super
  subclass.initialize_as_viewmodel
end

.initialize_as_viewmodel ⇒ Object 



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# File 'lib/view_model.rb', line 90

def initialize_as_viewmodel
  @_attributes    = []
  @schema_version = 1
  @view_aliases   = []
end

.is_update_hash?(hash) ⇒ Boolean

rubocop:disable Naming/PredicateName

Returns:

  • (Boolean) 


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# File 'lib/view_model.rb', line 188

def is_update_hash?(hash) # rubocop:disable Naming/PredicateName
  ViewModel::Schemas.verify_schema!(ViewModel::Schemas::VIEWMODEL_UPDATE, hash)
  hash.has_key?(ViewModel::ID_ATTRIBUTE) &&
    !hash.fetch(ViewModel::ActiveRecord::NEW_ATTRIBUTE, false)
end

.lock_attribute_inheritance ⇒ Object

An abstract viewmodel may want to define attributes to be shared by their subclasses. Redefine ‘_attributes` to close over the current class’s _attributes and ignore children.



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# File 'lib/view_model.rb', line 147

def lock_attribute_inheritance
  _attributes.tap do |attrs|
    define_singleton_method(:_attributes) { attrs }
    attrs.freeze
  end
end

.member_names ⇒ Object 



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# File 'lib/view_model.rb', line 154

def member_names
  _attributes.map(&:to_s)
end

.new_deserialize_context ⇒ Object 



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# File 'lib/view_model.rb', line 309

def new_deserialize_context(...)
  deserialize_context_class.new(...)
end

.new_serialize_context ⇒ Object 



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# File 'lib/view_model.rb', line 301

def new_serialize_context(...)
  serialize_context_class.new(...)
end

.preload_for_serialization(viewmodels, include_referenced: true, lock: nil) ⇒ Object 



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# File 'lib/view_model.rb', line 330

def preload_for_serialization(viewmodels, include_referenced: true, lock: nil)
  Array.wrap(viewmodels).group_by(&:class).each do |type, views|
    DeepPreloader.preload(views.map(&:model),
                          type.eager_includes(include_referenced: include_referenced),
                          lock: lock)
  end
end

.root! ⇒ Object 



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# File 'lib/view_model.rb', line 120

def root!
  define_singleton_method(:root?) { true }
end

.root? ⇒ Boolean

ViewModels are either roots or children. Root viewmodels may be (de)serialized directly, whereas child viewmodels are always nested within their parent. Associations to root viewmodel types always use indirect references.

Returns:

  • (Boolean) 


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# File 'lib/view_model.rb', line 116

def root?
  false
end

.schema_hash(schema_versions) ⇒ Object 



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# File 'lib/view_model.rb', line 323

def schema_hash(schema_versions)
  version_string = schema_versions.to_a.sort.join(',')
  # We want a short hash value, as this will be used in cache keys
  hash = Digest::SHA256.digest(version_string).byteslice(0, 16)
  Base64.urlsafe_encode64(hash, padding: false)
end

.schema_versions(viewmodels) ⇒ Object 



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# File 'lib/view_model.rb', line 317

def schema_versions(viewmodels)
  viewmodels.each_with_object({}) do |view, h|
    h[view.view_name] = view.schema_version
  end
end

.serialize(target, json, serialize_context: new_serialize_context) ⇒ Object

ViewModel can serialize ViewModels, Arrays and Hashes of ViewModels, and relies on Jbuilder#merge! for other values (e.g. primitives).



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# File 'lib/view_model.rb', line 203

def serialize(target, json, serialize_context: new_serialize_context)
  case target
  when ViewModel
    target.serialize(json, serialize_context: serialize_context)
  when Array
    json.array! target do |elt|
      serialize(elt, json, serialize_context: serialize_context)
    end
  when Hash, Struct
    json.merge!({})
    target.each_pair do |key, value|
      json.set! key do
        serialize(value, json, serialize_context: serialize_context)
      end
    end
  else
    json.merge! target
  end
end

.serialize_as_reference(target, json, serialize_context: new_serialize_context) ⇒ Object 



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# File 'lib/view_model.rb', line 223

def serialize_as_reference(target, json, serialize_context: new_serialize_context)
  if serialize_context.flatten_references
    serialize(target, json, serialize_context: serialize_context)
  else
    ref = serialize_context.add_reference(target)
    json.set!(REFERENCE_ATTRIBUTE, ref)
  end
end

.serialize_context_class ⇒ Object 



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# File 'lib/view_model.rb', line 297

def serialize_context_class
  ViewModel::SerializeContext
end

.serialize_from_cache(views, migration_versions: {}, locked: false, serialize_context:) ⇒ Object 



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# File 'lib/view_model.rb', line 236

def serialize_from_cache(views, migration_versions: {}, locked: false, serialize_context:)
  plural = views.is_a?(Array)
  views = Array.wrap(views)

  json_views, json_refs = ViewModel::ActiveRecord::Cache.render_viewmodels_from_cache(
                views, locked: locked, migration_versions: migration_versions, serialize_context: serialize_context)

  json_views = json_views.first unless plural
  return json_views, json_refs
end

.serialize_to_hash(viewmodel, serialize_context: new_serialize_context) ⇒ Object 



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# File 'lib/view_model.rb', line 232

def serialize_to_hash(viewmodel, serialize_context: new_serialize_context)
  Jbuilder.new { |json| serialize(viewmodel, json, serialize_context: serialize_context) }.attributes!
end

Instance Method Details

#==(other) ⇒ Object Also known as: eql? 



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# File 'lib/view_model.rb', line 421

def ==(other)
  other.class == self.class && self.class._attributes.all? do |attr|
    other.send(attr) == self.send(attr)
  end
end

#blame_reference ⇒ Object

When deserializing, if an error occurs within this viewmodel, what viewmodel is reported as to blame. Can be overridden for example when a viewmodel is merged with its parent.



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# File 'lib/view_model.rb', line 409

def blame_reference
  to_reference
end

#context_for_child(member_name, context:) ⇒ Object 



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# File 'lib/view_model.rb', line 413

def context_for_child(member_name, context:)
  context.for_child(self, association_name: member_name)
end

#hash ⇒ Object 



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# File 'lib/view_model.rb', line 429

def hash
  features = self.class._attributes.map { |attr| self.send(attr) }
  features << self.class
  features.hash
end

#id ⇒ Object

Provide a stable way to identify this view through attribute changes. By default views cannot make assumptions about the identity of our attributes, so we fall back on the view’s ‘object_id`. If a viewmodel is backed by a model with a concept of identity, this method should be overridden to use it.



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# File 'lib/view_model.rb', line 383

def id
  object_id
end

#model ⇒ Object

ViewModels are often used to serialize ActiveRecord models. For convenience, if necessary we assume that the wrapped model is the first attribute. To change this, override this method.



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# File 'lib/view_model.rb', line 374

def model
  self.public_send(self.class._attributes.first)
end

#preload_for_serialization(lock: nil) ⇒ Object 



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# File 'lib/view_model.rb', line 417

def preload_for_serialization(lock: nil)
  ViewModel.preload_for_serialization([self], lock: lock)
end

#serialize(json, serialize_context: self.class.new_serialize_context) ⇒ Object

Serialize this viewmodel to a jBuilder by calling serialize_view. May be overridden in subclasses to (for example) implement caching.



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# File 'lib/view_model.rb', line 347

def serialize(json, serialize_context: self.class.new_serialize_context)
  ViewModel::Callbacks.wrap_serialize(self, context: serialize_context) do
    serialize_view(json, serialize_context: serialize_context)
  end
end

#serialize_to_hash(serialize_context: self.class.new_serialize_context) ⇒ Object 



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# File 'lib/view_model.rb', line 353

def serialize_to_hash(serialize_context: self.class.new_serialize_context)
  Jbuilder.new { |json| serialize(json, serialize_context: serialize_context) }.attributes!
end

#serialize_view(json, serialize_context: self.class.new_serialize_context) ⇒ Object

Render this viewmodel to a jBuilder. Usually overridden in subclasses. Default implementation visits each attribute with Viewmodel.serialize.



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# File 'lib/view_model.rb', line 363

def serialize_view(json, serialize_context: self.class.new_serialize_context)
  self.class._attributes.each do |attr|
    json.set! attr do
      ViewModel.serialize(self.send(attr), json, serialize_context: serialize_context)
    end
  end
end

#stable_id? ⇒ Boolean

Is this viewmodel backed by a model with a stable identity? Used to decide whether the id is included when constructing a ViewModel::Reference from this view.

Returns:

  • (Boolean) 


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# File 'lib/view_model.rb', line 390

def stable_id?
  false
end

#to_json(serialize_context: self.class.new_serialize_context) ⇒ Object 



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# File 'lib/view_model.rb', line 357

def to_json(serialize_context: self.class.new_serialize_context)
  ViewModel.encode_json(self.serialize_to_hash(serialize_context: serialize_context))
end

#to_reference ⇒ Object 



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# File 'lib/view_model.rb', line 396

def to_reference
  ViewModel::Reference.new(self.class, (id if stable_id?))
end

#validate! ⇒ Object 



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# File 'lib/view_model.rb', line 394

def validate!; end

#view_name ⇒ Object

Delegate view_name to class in most cases. Polymorphic views may wish to override this to select a specific alias.



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# File 'lib/view_model.rb', line 402

def view_name
  self.class.view_name
end