Support conditional setting of serialization_scope in controllers

CHANGELOG.md

@@ -6,6 +6,7 @@ Breaking changes:
 - [#1662](https://github.com/rails-api/active_model_serializers/pull/1662) Drop support for Rails 4.0 and Ruby 2.0.0. (@remear)
 
 Features:
+- [#1711](https://github.com/rails-api/active_model_serializers/pull/1711) Set `serialization_scope` conditionally for specif actions in controller. (@yogeshjain999)
 - [#1699](https://github.com/rails-api/active_model_serializers/pull/1699) String/Lambda support for conditional attributes/associations (@mtsmfm)
 - [#1687](https://github.com/rails-api/active_model_serializers/pull/1687) Only calculate `_cache_digest` (in `cache_key`) when `skip_digest` is false. (@bf4)
 - [#1647](https://github.com/rails-api/active_model_serializers/pull/1647) Restrict usage of `serializable_hash` options

docs/general/serializers.md

@@ -302,6 +302,34 @@ So that when we render the `#edit` action, we'll get
 
 Where `can_edit` is `view_context.current_user.admin?` (true).
 
+You can optionally tell what to set as `serialization_scope` for specific actions,
+similar to `before_action` method in controllers.
+
+```diff
+class PostsController < ActionController::Base
+  serialization_scope :admin_user, only: :edit
+
+  def show
+    render json: @post, serializer: PostSerializer
+  end
+
+  def edit
+    @post.save
+    render json: @post, serializer: Admin::PostSerializer
+  end
+
+  private
+
+  def admin_user
+    User.new(id: 2, name: 'Bob', admin: true)
+  end
+
+  def current_user
+    User.new(id: 2, name: 'Bob', admin: false)
+  end
+end
+```
+
 #### #read_attribute_for_serialization(key)
 
 The serialized value for a given key. e.g. `read_attribute_for_serialization(:title) #=> 'Hello World'`

lib/action_controller/serialization.rb

@@ -8,8 +8,10 @@ module Serialization
     include ActionController::Renderers
 
     module ClassMethods
-      def serialization_scope(scope)
-        self._serialization_scope = scope
+      def serialization_scope(scope, opts = {})
+        before_action(opts.slice(:only, :except, :if, :unless)) do
+          self._serialization_scope = scope
+        end
       end
     end
 

test/action_controller/serialization_scope_name_test.rb

@@ -34,6 +34,12 @@ def json_key
   end
   class PostTestController < ActionController::Base
     attr_accessor :current_user
+
+    def render_post
+      self.current_user = User.new(id: 3, name: 'Pete')
+      render json: new_post, serializer: serializer, adapter: :json
+    end
+
     def render_post_by_non_admin
       self.current_user = User.new(id: 3, name: 'Pete', admin: false)
       render json: new_post, serializer: serializer, adapter: :json
@@ -71,10 +77,12 @@ class DefaultScopeTest < ActionController::TestCase
     tests PostTestController
 
     def test_default_serialization_scope
+      get :render_post
       assert_equal :current_user, @controller._serialization_scope
     end
 
     def test_default_serialization_scope_object
+      get :render_post
       assert_equal @controller.current_user, @controller.serialization_scope
     end
 
@@ -121,10 +129,12 @@ def serializer
     tests PostViewContextTestController
 
     def test_defined_serialization_scope
+      get :render_post
       assert_equal :view_context, @controller._serialization_scope
     end
 
     def test_defined_serialization_scope_object
+      get :render_post
       assert_equal @controller.view_context.class, @controller.serialization_scope.class
     end
 
@@ -158,6 +168,42 @@ def test_serialization_scope_admin
       assert_equal expected_json, @response.body
     end
   end
+  class ConditionalSerializationScopeTest < ActionController::TestCase
+    class PostConditionalViewContextTestController < PostTestController
+      serialization_scope :view_context, only: :render_post_by_admin
+
+      private
+
+      def serializer
+        PostViewContextSerializer
+      end
+    end
+
+    tests PostConditionalViewContextTestController
+
+    def test_conditional_serialization_scope_admin
+      get :render_post_by_admin
+      expected_json = {
+        post: {
+          id: 4,
+          title: 'Title',
+          body: "The 'scope' is the 'view_context': true",
+          comments: [
+            { id: 1, body: 'Admin' }
+          ]
+        }
+      }.to_json
+      assert_equal expected_json, @response.body
+    end
+
+    def test_conditional_serialization_scope_non_admin
+      exception_matcher = /view_context/
+      exception = assert_raises(NameError) do
+        get :render_post_by_non_admin
+      end
+      assert_match exception_matcher, exception.message
+    end
+  end
   class NilSerializationScopeTest < ActionController::TestCase
     class PostViewContextTestController < ActionController::Base
       serialization_scope nil
@@ -187,14 +233,6 @@ def new_post
     end
     tests PostViewContextTestController
 
-    def test_nil_serialization_scope
-      assert_nil @controller._serialization_scope
-    end
-
-    def test_nil_serialization_scope_object
-      assert_nil @controller.serialization_scope
-    end
-
     def test_nil_scope
       exception_matcher = /current_user/
       exception = assert_raises(NameError) do