Improvements on media type configs

By default, AMS responds to media type application/json and
application/vnd.api+json using the FlattenJson and JsonApi adapters
respectively. If you want to add a different media type, override the
defaults or even create your own, you can do it in your initializer.

Author: bacarini

README.md

@@ -51,16 +51,36 @@ end
 
 Generally speaking, you as a user of AMS will write (or generate) these
 serializer classes. If you want to use a different adapter, such as a JsonApi, you can
-change this in an initializer:
+change this in your render, or in an initializer:
 
 ```ruby
+#class
 ActiveModel::Serializer.config.adapter = ActiveModel::Serializer::Adapter::JsonApi
-```
 
+#symbol
+ActiveModel::Serializer.config.adapter = :json_api
+```
 or
 
 ```ruby
-ActiveModel::Serializer.config.adapter = :json_api
+render json: @posts, adapter: :json_api
+```
+
+You can use `Accept` HTTP header-field to select a specific adapter by enabling it.
+
+```ruby
+ActiveModel::Serializer.config.enabled_adapters_by_media_type = true
+```
+By default, AMS responds to media type `application/json` and `application/vnd.api+json` using the `FlattenJson` and `JsonApi` adapters respectively. If you want to add a different media type,  override the defaults or even create your own, you can do it in your initializer.
+
+To override media type `application/json` to respond with `Json` instead of `FlattenJson` adapter:
+```ruby
+ActiveModel::Serializer.config.custom_media_type_adapters = {"application/json" => :json}
+```
+
+If you have a custom adapter (`xml`, as example) you can create your own media type:
+```ruby
+ActiveModel::Serializer.config.custom_media_type_adapters = {"application/xml" => :xml}
 ```
 
 You won't need to implement an adapter unless you wish to use a new format or

lib/action_controller/serialization.rb

@@ -26,7 +26,7 @@ def get_serializer(resource, options = {})
         options[:adapter] = false
       end
 
-      unless options[:adapter]
+      if ActiveModel::Serializer.enabled_adapters_by_media_type && !options.fetch(:adapter, nil)
         adapter = ActiveModel::Serializer::Adapter.by_request(request)
         options[:adapter] ||= adapter if adapter
       end

lib/active_model/serializer.rb

@@ -104,20 +104,12 @@ def self.adapter
       adapter_class
     end
 
-    def self.custom_media_type_adapters=(media_type_adapters)
-      config.custom_media_type_adapters ||= {}
-
-      unless media_type_adatets.is_a? Array
-        media_types_adapters = [media_types_adapters]
-      end
-
-      media_types_adapters.each do |media_type_adapter|
-        config.custom_media_type_adapters.merge!(media_type_adapter)
-      end
+    def self.custom_media_type_adapters
+      config.custom_media_type_adapters
     end
 
-    def self.custom_media_type_adapters
-      config.custom_media_type_adapters ||= {}
+    def self.enabled_adapters_by_media_type
+      config.enabled_adapters_by_media_type
     end
 
     def self.root_name

lib/active_model/serializer/configuration.rb

@@ -7,6 +7,8 @@ module Configuration
       included do |base|
         base.config.array_serializer = ActiveModel::Serializer::ArraySerializer
         base.config.adapter = :flatten_json
+        base.config.enabled_adapters_by_media_type = true
+        base.config.custom_media_type_adapters = {}
       end
     end
   end

test/action_controller/adapter_selector_test.rb

@@ -55,6 +55,7 @@ def test_render_skipping_adapter
       end
 
       def test_render_using_adapter_selected_by_accept_header_field
+        ActiveModel::Serializer.config.enabled_adapters_by_media_type = true
         request.headers['Accept'] = "application/vnd.api+json"
 
         get :render_selecting_adapter_by_accept_header_field