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/error_wrapping.rb,
lib/view_model/deserialization_error.rb

Defined Under Namespace

Modules: AfterTransactionRunner, Callbacks, Controller, ErrorWrapping, 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.



351
352
353
354
355
 
# File 'lib/view_model.rb', line 351

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.



72
73
74
 
# File 'lib/view_model.rb', line 72

def _attributes
  @_attributes
end

.schema_version ⇒ Object

Returns the value of attribute schema_version.



73
74
75
 
# 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.



83
84
85
 
# File 'lib/view_model.rb', line 83

def synthetic
  @synthetic
end

.view_aliases ⇒ Object (readonly)

Returns the value of attribute view_aliases.



74
75
76
 
# File 'lib/view_model.rb', line 74

def view_aliases
  @view_aliases
end

.view_name ⇒ Object 



96
97
98
99
100
101
102
103
104
105
 
# 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) 


322
323
324
 
# File 'lib/view_model.rb', line 322

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

.add_view_alias(as) ⇒ Object 



107
108
109
110
 
# 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 



131
132
133
134
135
136
137
138
139
140
141
142
 
# 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.



127
128
129
 
# File 'lib/view_model.rb', line 127

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

.deserialization_includes ⇒ Object

If this viewmodel represents an AR model, what associations does it make use of during deserialization? By default all mentioned associations are preloaded, however access controls and hooks may benefit from additional preloading. Returns a includes spec appropriate for DeepPreloader, either as AR-style nested hashes or DeepPreloader::Spec.



206
207
208
 
# File 'lib/view_model.rb', line 206

def deserialization_includes
  {}
end

.deserialize_context_class ⇒ Object 



314
315
316
 
# File 'lib/view_model.rb', line 314

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.



268
269
270
271
272
 
# File 'lib/view_model.rb', line 268

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 



274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
 
# File 'lib/view_model.rb', line 274

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 during serialization? Returns a includes spec appropriate for DeepPreloader, either as AR-style nested hashes or DeepPreloader::Spec.



197
198
199
 
# File 'lib/view_model.rb', line 197

def eager_includes(include_referenced: true)
  {}
end

.encode_json(value) ⇒ Object 



256
257
258
259
260
261
262
263
264
265
 
# File 'lib/view_model.rb', line 256

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 



183
184
185
186
 
# 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 



175
176
177
178
179
180
181
 
# 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.



159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
 
# 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 



85
86
87
88
 
# File 'lib/view_model.rb', line 85

def inherited(subclass)
  super
  subclass.initialize_as_viewmodel
end

.initialize_as_viewmodel ⇒ Object 



90
91
92
93
94
 
# 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) 


188
189
190
191
192
 
# 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.



147
148
149
150
151
152
 
# 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 



154
155
156
 
# File 'lib/view_model.rb', line 154

def member_names
  _attributes.map(&:to_s)
end

.new_deserialize_context ⇒ Object 



318
319
320
 
# File 'lib/view_model.rb', line 318

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

.new_serialize_context ⇒ Object 



310
311
312
 
# File 'lib/view_model.rb', line 310

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

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



339
340
341
342
343
344
345
346
347
348
 
# File 'lib/view_model.rb', line 339

def preload_for_serialization(viewmodels, include_referenced: true, lock: nil)
  Array.wrap(viewmodels)
    .flat_map { |v| v.preloadable_dependencies(include_referenced: include_referenced) }
    .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 



120
121
122
 
# 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) 


116
117
118
 
# File 'lib/view_model.rb', line 116

def root?
  false
end

.schema_hash(schema_versions) ⇒ Object 



332
333
334
335
336
337
 
# File 'lib/view_model.rb', line 332

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 



326
327
328
329
330
 
# File 'lib/view_model.rb', line 326

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).



212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
 
# File 'lib/view_model.rb', line 212

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 



232
233
234
235
236
237
238
239
 
# File 'lib/view_model.rb', line 232

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 



306
307
308
 
# File 'lib/view_model.rb', line 306

def serialize_context_class
  ViewModel::SerializeContext
end

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



245
246
247
248
249
250
251
252
253
254
 
# File 'lib/view_model.rb', line 245

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 



241
242
243
 
# File 'lib/view_model.rb', line 241

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? 



441
442
443
444
445
 
# File 'lib/view_model.rb', line 441

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.



421
422
423
 
# File 'lib/view_model.rb', line 421

def blame_reference
  to_reference
end

#context_for_child(member_name, context:) ⇒ Object 



425
426
427
 
# File 'lib/view_model.rb', line 425

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

#hash ⇒ Object 



449
450
451
452
453
 
# File 'lib/view_model.rb', line 449

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.



395
396
397
 
# File 'lib/view_model.rb', line 395

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.



386
387
388
 
# File 'lib/view_model.rb', line 386

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

#preload_for_serialization(include_referenced: true, lock: nil) ⇒ Object 



429
430
431
 
# File 'lib/view_model.rb', line 429

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

#preloadable_dependencies(include_referenced: true) ⇒ Object

Returns a collection of zero or more AR-backed views that this view depends on that can have their dependencies preloaded via eager_includes. This can be overridden for non-AR view that wrap AR-backed views to expose those dependencies for preloading.



437
438
439
 
# File 'lib/view_model.rb', line 437

def preloadable_dependencies(include_referenced: true)
  []
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.



359
360
361
362
363
 
# File 'lib/view_model.rb', line 359

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 



365
366
367
 
# File 'lib/view_model.rb', line 365

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.



375
376
377
378
379
380
381
 
# File 'lib/view_model.rb', line 375

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) 


402
403
404
 
# File 'lib/view_model.rb', line 402

def stable_id?
  false
end

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



369
370
371
 
# File 'lib/view_model.rb', line 369

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 



408
409
410
 
# File 'lib/view_model.rb', line 408

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

#validate! ⇒ Object 



406
 
# File 'lib/view_model.rb', line 406

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.



414
415
416
 
# File 'lib/view_model.rb', line 414

def view_name
  self.class.view_name
end