Introduces per-request adapter switching based on the request mime.

CHANGELOG.md

@@ -6,6 +6,8 @@ Breaking changes:
 
 Features:
 
+- [#2122](https://github.com/rails-api/active_model_serializers/pull/2122) Introduces per-request adapter switching based on the request mime. (@fletcher91)
+
 Fixes:
 
 Misc:

docs/general/adapters.md

@@ -36,6 +36,20 @@ The `Attributes` adapter does not include a root key. It is just the serialized
 
 Use either the `JSON` or `JSON API` adapters if you want the response document to have a root key.
 
+To automatically switch between adapters based on the request, set the adapter to `:mime`
+
+```ruby
+  # In configuration
+  ActiveModelSerializers.config.adapter = :mime
+
+  # In controller action
+  respond_to do |format|
+    format.json { render json: Model.first }     # Uses the JSON adapter
+    format.json_api { render json: Model.first } # Users the JSON:API adapter
+    format.bug { render json: Model.first } # Will raise `UnknownAdapterError`
+  end
+```
+
 ## Built in Adapters
 
 ### Attributes - Default

lib/active_model_serializers/adapter.rb

@@ -19,6 +19,11 @@ def configured_adapter
 
       def create(resource, options = {})
         override = options.delete(:adapter)
+        context = options[:serialization_context]
+        format = context && context.format
+        if format && (override || ActiveModelSerializers.config.adapter) == :mime
+          override = lookup(format)
+        end
         klass = override ? adapter_class(override) : configured_adapter
         klass.new(resource, options)
       end

lib/active_model_serializers/serialization_context.rb

@@ -21,15 +21,17 @@ def default_url_options
       end
     end
 
-    attr_reader :request_url, :query_parameters, :key_transform
+    attr_reader :request_url, :query_parameters, :key_transform, :format
 
     def initialize(*args)
       options = args.extract_options!
       if args.size == 1
         request = args.pop
+        options[:format] = request.format.to_sym
         options[:request_url] = request.original_url[/\A[^?]+/]
         options[:query_parameters] = request.query_parameters
       end
+      @format = options.delete(:format)
       @request_url = options.delete(:request_url)
       @query_parameters = options.delete(:query_parameters)
       @url_helpers = options.delete(:url_helpers) || self.class.url_helpers

test/adapter/json/transform_test.rb

@@ -8,6 +8,7 @@ def mock_request(key_transform = nil)
           context = Minitest::Mock.new
           context.expect(:request_url, URI)
           context.expect(:query_parameters, {})
+          context.expect(:format, Mime::Type.new(:json))
           options = {}
           options[:key_transform] = key_transform if key_transform
           options[:serialization_context] = context

test/adapter/json_api/pagination_links_test.rb

@@ -26,6 +26,7 @@ def mock_request(query_parameters = {}, original_url = URI)
           context.expect(:request_url, original_url)
           context.expect(:query_parameters, query_parameters)
           context.expect(:key_transform, nil)
+          context.expect(:format, Mime::Type.new(:json_api))
         end
 
         def load_adapter(paginated_collection, mock_request = nil)

test/adapter_test.rb

@@ -55,6 +55,16 @@ def test_create_adapter_with_override
       assert_equal ActiveModelSerializers::Adapter::JsonApi, adapter.class
     end
 
+    def test_create_adapter_with_mime
+      json_context = ActiveModelSerializers::SerializationContext.new(format: :json)
+      adapter = ActiveModelSerializers::Adapter.create(@serializer, adapter: :mime, serialization_context: json_context)
+      assert_equal ActiveModelSerializers::Adapter::Json, adapter.class
+
+      json_api_context = ActiveModelSerializers::SerializationContext.new(format: :json_api)
+      adapter = ActiveModelSerializers::Adapter.create(@serializer, adapter: :mime, serialization_context: json_api_context)
+      assert_equal ActiveModelSerializers::Adapter::JsonApi, adapter.class
+    end
+
     def test_inflected_adapter_class_for_known_adapter
       ActiveSupport::Inflector.inflections(:en) { |inflect| inflect.acronym 'API' }
       klass = ActiveModelSerializers::Adapter.adapter_class(:json_api)