Rails: Switches Serializer according to STI Type
Introduction
Hello, here is Tamura.
Suppose you have model data of multiple types using STI and want to mix and return them in a single API endpoint. In this case, you would like to switch the serializer according to the STI type.
In this article, I will show you how to do this.
Issue
Suppose the following class hierarchy is realized in STI
SimplePosts has a title and body field, and QAPosts has a question and answer field. They all have a common posted_at field.
Suppose you define an API endpoint called /api/v1/posts and want to return JSON as follows:
Depending on whether the Posts type is SimplePost or QAPost, the JSON keys will differ.
If you are using ActiveModel::Serializers to output JSON, you will need to switch the Serializer depending on the type of Posts.
Solution
The code is shown below.
app/serializers/post_serializer.rb
app/serializers/simple_post_serializer.rb
app/serializers/qa_post_serializer.rb
app/controllers/api/v1/posts_controller.rb
Override the attributes method in PostSerializer. Since each data is taken as an object, the class is determined in case, and SimplePostSerializer.new(object).attributes(nil,reload) and QAPostSerializer.new(object).attributes(nil,reload) generates attributes and merges them into@attributes.
The reason for overriding the json_key method is to display posts in the json toplevel object. If this is not defined, qa_posts and the type first processed by the Serializer will be set as the key, as shown below.
Note that if jsonapi_include_toplevel_object is false, there is no need to override the json_key method.
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