Basic deserialization.

CHANGELOG.md

@@ -16,6 +16,7 @@ Breaking changes:
 
 Features:
 
+- [#1248](https://github.com/rails-api/active_model_serializers/pull/1248) Experimental: Add support for JSON API deserialization (@beauby)
 - [#1378](https://github.com/rails-api/active_model_serializers/pull/1378) Change association blocks
   to be evaluated in *serializer* scope, rather than *association* scope. (@bf4)
     * Syntax changes from e.g.

lib/active_model/serializer/adapter/json_api.rb

@@ -6,6 +6,7 @@ class JsonApi < Base
         autoload :PaginationLinks
         autoload :FragmentCache
         autoload :Link
+        autoload :Deserialization
 
         # TODO: if we like this abstraction and other API objects to it,
         # then extract to its own file and require it.

lib/active_model/serializer/adapter/json_api/deserialization.rb

@@ -0,0 +1,207 @@
+module ActiveModel
+  class Serializer
+    module Adapter
+      class JsonApi
+        # NOTE(Experimental):
+        # This is an experimental feature. Both the interface and internals could be subject
+        # to changes.
+        module Deserialization
+          InvalidDocument = Class.new(ArgumentError)
+
+          module_function
+
+          # Transform a JSON API document, containing a single data object,
+          # into a hash that is ready for ActiveRecord::Base.new() and such.
+          # Raises InvalidDocument if the payload is not properly formatted.
+          #
+          # @param [Hash|ActionController::Parameters] document
+          # @param [Hash] options
+          #   only: Array of symbols of whitelisted fields.
+          #   except: Array of symbols of blacklisted fields.
+          #   keys: Hash of translated keys (e.g. :author => :user).
+          #   polymorphic: Array of symbols of polymorphic fields.
+          # @return [Hash]
+          #
+          # @example
+          #   document = {
+          #     data: {
+          #       id: 1,
+          #       type: 'post',
+          #       attributes: {
+          #         title: 'Title 1',
+          #         date: '2015-12-20'
+          #       },
+          #       associations: {
+          #         author: {
+          #           data: {
+          #             type: 'user',
+          #             id: 2
+          #           }
+          #         },
+          #         second_author: {
+          #           data: nil
+          #         },
+          #         comments: {
+          #           data: [{
+          #             type: 'comment',
+          #             id: 3
+          #           },{
+          #             type: 'comment',
+          #             id: 4
+          #           }]
+          #         }
+          #       }
+          #     }
+          #   }
+          #
+          #   parse(document) #=>
+          #     # {
+          #     #   title: 'Title 1',
+          #     #   date: '2015-12-20',
+          #     #   author_id: 2,
+          #     #   second_author_id: nil
+          #     #   comment_ids: [3, 4]
+          #     # }
+          #
+          #   parse(document, only: [:title, :date, :author],
+          #                   keys: { date: :published_at },
+          #                   polymorphic: [:author]) #=>
+          #     # {
+          #     #   title: 'Title 1',
+          #     #   published_at: '2015-12-20',
+          #     #   author_id: '2',
+          #     #   author_type: 'people'
+          #     # }
+          #
+          def parse!(document, options = {})
+            parse(document, options) do |invalid_payload, reason|
+              fail InvalidDocument, "Invalid payload (#{reason}): #{invalid_payload}"
+            end
+          end
+
+          # Same as parse!, but returns an empty hash instead of raising InvalidDocument
+          # on invalid payloads.
+          def parse(document, options = {})
+            document = document.dup.permit!.to_h if document.is_a?(ActionController::Parameters)
+
+            validate_payload(document) do |invalid_document, reason|
+              yield invalid_document, reason if block_given?
+              return {}
+            end
+
+            primary_data = document['data']
+            attributes = primary_data['attributes'] || {}
+            attributes['id'] = primary_data['id'] if primary_data['id']
+            relationships = primary_data['relationships'] || {}
+
+            filter_fields(attributes, options)
+            filter_fields(relationships, options)
+
+            hash = {}
+            hash.merge!(parse_attributes(attributes, options))
+            hash.merge!(parse_relationships(relationships, options))
+
+            hash
+          end
+
+          # Checks whether a payload is compliant with the JSON API spec.
+          #
+          # @api private
+          # rubocop:disable Metrics/CyclomaticComplexity
+          def validate_payload(payload)
+            unless payload.is_a?(Hash)
+              yield payload, 'Expected hash'
+              return
+            end
+
+            primary_data = payload['data']
+            unless primary_data.is_a?(Hash)
+              yield payload, { data: 'Expected hash' }
+              return
+            end
+
+            attributes = primary_data['attributes'] || {}
+            unless attributes.is_a?(Hash)
+              yield payload, { data: { attributes: 'Expected hash or nil' } }
+              return
+            end
+
+            relationships = primary_data['relationships'] || {}
+            unless relationships.is_a?(Hash)
+              yield payload, { data: { relationships: 'Expected hash or nil' } }
+              return
+            end
+
+            relationships.each do |(key, value)|
+              unless value.is_a?(Hash) && value.key?('data')
+                yield payload, { data: { relationships: { key => 'Expected hash with :data key' } } }
+              end
+            end
+          end
+          # rubocop:enable Metrics/CyclomaticComplexity
+
+          # @api private
+          def filter_fields(fields, options)
+            if (only = options[:only])
+              fields.slice!(*Array(only).map(&:to_s))
+            elsif (except = options[:except])
+              fields.except!(*Array(except).map(&:to_s))
+            end
+          end
+
+          # @api private
+          def field_key(field, options)
+            (options[:keys] || {}).fetch(field.to_sym, field).to_sym
+          end
+
+          # @api private
+          def parse_attributes(attributes, options)
+            attributes
+              .map { |(k, v)| { field_key(k, options) => v } }
+              .reduce({}, :merge)
+          end
+
+          # Given an association name, and a relationship data attribute, build a hash
+          # mapping the corresponding ActiveRecord attribute to the corresponding value.
+          #
+          # @example
+          #   parse_relationship(:comments, [{ 'id' => '1', 'type' => 'comments' },
+          #                                  { 'id' => '2', 'type' => 'comments' }],
+          #                                 {})
+          #    # => { :comment_ids => ['1', '2'] }
+          #   parse_relationship(:author, { 'id' => '1', 'type' => 'users' }, {})
+          #    # => { :author_id => '1' }
+          #   parse_relationship(:author, nil, {})
+          #    # => { :author_id => nil }
+          # @param [Symbol] assoc_name
+          # @param [Hash] assoc_data
+          # @param [Hash] options
+          # @return [Hash{Symbol, Object}]
+          #
+          # @api private
+          def parse_relationship(assoc_name, assoc_data, options)
+            prefix_key = field_key(assoc_name, options).to_s.singularize
+            hash =
+              if assoc_data.is_a?(Array)
+                { "#{prefix_key}_ids".to_sym => assoc_data.map { |ri| ri['id'] } }
+              else
+                { "#{prefix_key}_id".to_sym => assoc_data ? assoc_data['id'] : nil }
+              end
+
+            polymorphic = (options[:polymorphic] || []).include?(assoc_name.to_sym)
+            hash.merge!("#{prefix_key}_type".to_sym => assoc_data['type']) if polymorphic
+
+            hash
+          end
+
+          # @api private
+          def parse_relationships(relationships, options)
+            relationships
+              .map { |(k, v)| parse_relationship(k, v['data'], options) }
+              .reduce({}, :merge)
+          end
+        end
+      end
+    end
+  end
+end

lib/active_model_serializers.rb

@@ -12,6 +12,7 @@ def self.config
   extend ActiveSupport::Autoload
   autoload :Model
   autoload :Callbacks
+  autoload :Deserialization
   autoload :Logging
 end
 

lib/active_model_serializers/deserialization.rb

@@ -0,0 +1,13 @@
+module ActiveModelSerializers
+  module Deserialization
+    module_function
+
+    def jsonapi_parse(*args)
+      ActiveModel::Serializer::Adapter::JsonApi::Deserialization.parse(*args)
+    end
+
+    def jsonapi_parse!(*args)
+      ActiveModel::Serializer::Adapter::JsonApi::Deserialization.parse!(*args)
+    end
+  end
+end

test/action_controller/json_api/deserialization_test.rb

@@ -0,0 +1,59 @@
+require 'test_helper'
+
+module ActionController
+  module Serialization
+    class JsonApi
+      class DeserializationTest < ActionController::TestCase
+        class DeserializationTestController < ActionController::Base
+          def render_parsed_payload
+            parsed_hash = ActiveModelSerializers::Deserialization.jsonapi_parse(params)
+            render json: parsed_hash
+          end
+        end
+
+        tests DeserializationTestController
+
+        def test_deserialization
+          hash = {
+            'data' => {
+              'type' => 'photos',
+              'id' => 'zorglub',
+              'attributes' => {
+                'title' => 'Ember Hamster',
+                'src' => 'http://example.com/images/productivity.png'
+              },
+              'relationships' => {
+                'author' => {
+                  'data' => nil
+                },
+                'photographer' => {
+                  'data' => { 'type' => 'people', 'id' => '9' }
+                },
+                'comments' => {
+                  'data' => [
+                    { 'type' => 'comments', 'id' => '1' },
+                    { 'type' => 'comments', 'id' => '2' }
+                  ]
+                }
+              }
+            }
+          }
+
+          post :render_parsed_payload, hash
+
+          response = JSON.parse(@response.body)
+          expected = {
+            'id' => 'zorglub',
+            'title' => 'Ember Hamster',
+            'src' => 'http://example.com/images/productivity.png',
+            'author_id' => nil,
+            'photographer_id' => '9',
+            'comment_ids' => %w(1 2)
+          }
+
+          assert_equal(expected, response)
+        end
+      end
+    end
+  end
+end