Merge pull request #1545 from CodedBeardedSignedTaylor/1506-document-…

…passing-arbitrary-options-to-serializer

[DOCS] 1506 document passing arbitrary options to serializer

docs/README.md

@@ -25,6 +25,7 @@ This is the documentation of ActiveModelSerializers, it's focused on the **0.10.
 - [How to add pagination links](howto/add_pagination_links.md)
 - [Using ActiveModelSerializers Outside Of Controllers](howto/outside_controller_use.md)
 - [Testing ActiveModelSerializers](howto/test.md)
+- [Passing Arbitrary Options](howto/passing_arbitrary_options.md)
 
 ## Integrations
 

docs/howto/passing_arbitrary_options.md

@@ -0,0 +1,27 @@
+[Back to Guides](../README.md)
+
+# Passing Arbitrary Options To A Serializer
+
+In addition to the [`serialization_scope`](../general/serializers.md#scope), any options passed to `render`
+that are not reserved for the [adapter](../general/rendering.md#adapter_opts)
+are available in the serializer as [instance_options](../general/serializers.md#instance_options).
+
+For example, we could pass in a field, such as `user_id` into our serializer.
+
+```ruby
+# posts_controller.rb
+class PostsController < ApplicationController
+  def dashboard  
+    render json: @post, user_id: 12
+  end
+end
+
+# post_serializer.rb
+class PostSerializer < ActiveModel::Serializer
+  attributes :id, :title, :body
+
+  def comments_by_me  
+    Comments.where(user_id: instance_options[:user_id], post_id: object.id)
+  end
+end
+```