Read only (immutable) relationships

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• Problem/bug report.
• [ x ] Feature request.
• Request for support. Note: Please try to avoid submitting issues for support requests. Use Gitter instead.

Checklist before submitting:

• I've searched for an existing issue.
• I've asked my question on Gitter and have not received a satisfactory answer.
• I've included a complete bug report template. This step helps us and allows us to see the bug without trying to reproduce the problem from your description. It helps you because you will frequently detect if it's a problem specific to your project.
• The feature I'm asking for is compliant with the JSON:API spec.

Description

Features:

As an engineer I would like to add has_many or has_one relations which are read only. To accomplish this on the current implementation the following code is used in the resource file.

has_many :cars

def cars=(_cars); end

Start in the resource implementation that handles has_many and has_one declarations, using the example resource definition as the entry point. Trace how relationship writers are generated or invoked, then add declarative support for read-only relationships and locate the relevant relationship tests to verify that the custom setter workaround is no longer needed.