Rails uses a two-step process for JSON serialization. First, as_json converts the object to a hash representation. Then,
to_json converts that hash to a JSON string.
When you override to_json in an ActiveRecord model, you break Rails' JSON rendering pipeline. The render json: method in
controllers expects to call as_json on your model, but if you’ve overridden to_json, this can lead to several problems:
- ArgumentError exceptions: The
to_json method signature may not match what Rails expects, causing "wrong number of
arguments" errors.
- Broken controller rendering: Using
render json: @model may not work as expected because Rails calls
as_json internally, not your custom to_json method.
- Inconsistent behavior: Your custom serialization will only work when
to_json is called directly, not through
Rails' standard JSON rendering.
The as_json method is specifically designed to be overridden. It receives an options hash that you can merge with your custom options,
making it flexible and compatible with Rails' rendering system.
What is the potential impact?
Overriding to_json instead of as_json can cause runtime errors in your Rails application, particularly ArgumentError
exceptions when using render json: in controllers. This can lead to broken API endpoints and inconsistent JSON serialization behavior
across your application.
