Properly deserialize dasherized keys

The JSON API adapater dasherizes every key, but the deserializer left the keys
unaltered. Thus, the client had to send underscored keys in the request body in
order for Rails to properly match sent values to model attributes.

This commit adds automatic key transformation on deserialization. Per default the
deserializer transforms the keys to underscore, but this behaviour can also be
changed by including `key_transform` in the deserializer options.

lib/active_model_serializers/adapter/json_api/deserialization.rb

@@ -155,7 +155,7 @@ module ActiveModelSerializers
 
         # @api private
         def parse_attributes(attributes, options)
-          attributes
+          transform_keys(attributes, options)
             .map { |(k, v)| { field_key(k, options) => v } }
             .reduce({}, :merge)
         end
@@ -182,23 +182,29 @@ module ActiveModelSerializers
           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'] } }
+              { "#{prefix_key}_ids".to_sym => assoc_data.map { |ri| ri[:id] } }
             else
-              { "#{prefix_key}_id".to_sym => assoc_data ? assoc_data['id'] : nil }
+              { "#{prefix_key}_id".to_sym => assoc_data && assoc_data.is_a?(Hash) ? assoc_data[:id] : nil }
             end
 
           polymorphic = (options[:polymorphic] || []).include?(assoc_name.to_sym)
-          hash["#{prefix_key}_type".to_sym] = assoc_data['type'] if polymorphic
+          hash["#{prefix_key}_type".to_sym] = assoc_data[:type] if polymorphic
 
           hash
         end
 
         # @api private
         def parse_relationships(relationships, options)
-          relationships
+          transform_keys(relationships, options)
-            .map { |(k, v)| parse_relationship(k, v['data'], options) }
+            .map { |(k, v)| parse_relationship(k, v[:data], options) }
             .reduce({}, :merge)
         end
+
+        # @api private
+        def transform_keys(hash, options)
+          transform = options[:key_transform] || :underscore
+          KeyTransform.send(transform, hash)
+        end
       end
     end
   end

lib/active_model_serializers/key_transform.rb

@@ -32,6 +32,16 @@ module ActiveModelSerializers
       hash.deep_transform_keys! { |key| key.to_s.dasherize.to_sym }
     end
 
+    # Transforms keys to underscore.
+    # This is the default case for deserialization in the JsonApi adapter.
+    #
+    # @example:
+    #    "some-key" => "some_key",
+    # @see {https://github.com/rails/rails/blob/master/activesupport/lib/active_support/inflector/methods.rb#L89-L98 ActiveSupport::Inflector.underscore}
+    def underscore(hash)
+      hash.deep_transform_keys! { |key| key.to_s.underscore.to_sym }
+    end
+
     # Returns the hash unaltered
     def unaltered(hash)
       hash

test/action_controller/json_api/deserialization_test.rb

@@ -20,7 +20,10 @@ module ActionController
               'id' => 'zorglub',
               'attributes' => {
                 'title' => 'Ember Hamster',
-                'src' => 'http://example.com/images/productivity.png'
+                'src' => 'http://example.com/images/productivity.png',
+                'image-width' => '200',
+                'imageHeight' => '200',
+                'ImageSize' => '1024'
               },
               'relationships' => {
                 'author' => {
@@ -34,6 +37,12 @@ module ActionController
                     { 'type' => 'comments', 'id' => '1' },
                     { 'type' => 'comments', 'id' => '2' }
                   ]
+                },
+                'related-images' => {
+                  'data' => [
+                    { 'type' => 'image', 'id' => '7' },
+                    { 'type' => 'image', 'id' => '8' }
+                  ]
                 }
               }
             }
@@ -46,9 +55,13 @@ module ActionController
             'id' => 'zorglub',
             'title' => 'Ember Hamster',
             'src' => 'http://example.com/images/productivity.png',
+            'image_width' => '200',
+            'image_height' => '200',
+            'image_size' => '1024',
             'author_id' => nil,
             'photographer_id' => '9',
-            'comment_ids' => %w(1 2)
+            'comment_ids' => %w(1 2),
+            'related_image_ids' => %w(7 8)
           }
 
           assert_equal(expected, response)