[WIP] Add basic support for ActiveModel::Errors.

Gemfile

@@ -1,3 +1,6 @@
 source 'https://rubygems.org'
 
+gem 'jsonapi-deserializable', '0.1.1.beta3',
+    github: 'jsonapi-rb/deserializable', branch: 'reverse-mapping'
+
 gemspec

lib/jsonapi/rails/action_controller.rb

@@ -7,6 +7,17 @@ module ActionController
       def self.included(base)
         base.class_eval do
           extend ClassMethods
+          prepend InstanceMethods
+        end
+      end
+
+      module InstanceMethods
+        def render(opts = {})
+          if opts.key?(:jsonapi_error)
+            mapping = params.to_unsafe_h[:_jsonapi_mapping]
+            opts = opts.merge(_jsonapi_mapping: mapping)
+          end
+          super(opts)
         end
       end
 
@@ -42,16 +53,23 @@ def call(env)
           request = Rack::Request.new(env)
           body = request.params.slice(*JSONAPI_KEYS)
           parser.parse!(body)
-          deserialized_hash = @deserializable_class.call(body)
+          deserialize!(request, body)
+
+          @app.call(env)
+        end
+
+        def deserialize!(request, body)
+          deserialized = @deserializable_class.new(body)
+          deserialized_hash = deserialized.to_h
+          mapping = deserialized.mapping
           jsonapi = {}
           JSONAPI_KEYS.each do |key|
             next unless request.params.key?(key)
             jsonapi[key.to_sym] = request.delete_param(key)
           end
           request.update_param(:_jsonapi, jsonapi)
+          request.update_param(:_jsonapi_mapping, mapping)
           request.update_param(@deserializable_key, deserialized_hash)
-
-          @app.call(env)
         end
       end
 

lib/jsonapi/rails/railtie.rb

@@ -2,13 +2,11 @@
 require 'action_controller'
 require 'active_support'
 
-require 'jsonapi/rails/parser'
-require 'jsonapi/rails/renderer'
-
 module JSONAPI
   module Rails
     class Railtie < ::Rails::Railtie
       MEDIA_TYPE = 'application/vnd.api+json'.freeze
+      require 'jsonapi/rails/parser'
       PARSER = JSONAPI::Rails.parser
 
       initializer 'jsonapi-rails.action_controller' do
@@ -23,6 +21,7 @@ class Railtie < ::Rails::Railtie
             ::ActionDispatch::ParamsParser::DEFAULT_PARSERS[Mime[:jsonapi]] = PARSER
           end
 
+          require 'jsonapi/rails/renderer'
           ::ActionController::Renderers.add :jsonapi do |json, options|
             unless json.is_a?(String)
               json = JSONAPI::Rails::Renderer.render(json, options)
@@ -33,7 +32,7 @@ class Railtie < ::Rails::Railtie
 
           ::ActionController::Renderers.add :jsonapi_errors do |json, options|
             unless json.is_a?(String)
-              json = JSONAPI::Rails::ErrorRender.render_errors(json, options)
+              json = JSONAPI::Rails::ErrorRenderer.render(json, options)
             end
             self.content_type ||= Mime[:jsonapi]
             self.response_body = json

lib/jsonapi/rails/renderer.rb

@@ -18,9 +18,25 @@ def self.render(resources, options)
 
     class ErrorRenderer
       def self.render(errors, options)
-        # TODO(beauby): SerializableError inference on AR validation errors.
+        if errors.is_a?(ActiveModel::Errors)
+          errors = build_active_model_errors(errors, options[:_jsonapi_mapping])
+        end
         JSONAPI::Serializable::ErrorRenderer.render(errors, options)
       end
+
+      def self.build_active_model_errors(errors, mapping)
+        error_class = Class.new(JSONAPI::Serializable::Error) do
+          detail { @detail }
+          source do
+            path, name = @attribute
+            pointer "#{path}/#{name}"
+          end
+        end
+        errors.map! do |attr, error|
+          attr = mapping[attr]
+          error_class.new(attribute: attr, detail: error)
+        end
+      end
     end
   end
 end