Use model assemblers for HATEOAS responses

• Status: accepted
• Deciders: [QuAntiL EnPro Team]

Context and Problem Statement

Spring HATEOAS includes several classes that encapsulate domain objects, adding support for links. Constructing such objects, as well as adding the desired links to them is a common operation that requires entity-specific boilerplate code. How can duplicate code in nearly all controller methods be avoided?

Decision Drivers

• Avoid duplicate code to create HATEOAS models
• Decouple link creation from normal entity logic

Considered Options

• Make links part of the entity objects and use inheritance
• Separate model assembler classes

Decision Outcome

Separate model assemblers were chosen, as the former option would require us to have a deep coupling between HATEOAS types and our DTO classes.

Due to the assembler classes being initially only used for links they all reside in the linkassembler package.

Pros and Cons of the Options

Make links part of the entity objects and use inheritance

• Good: easy to implement
• Bad: Deep coupling between Spring HATEOAS internals and our types

Separate model assembler classes

• Good: Clear separation of concerns
• Bad: More complex implementation, especially if call sites are to be kept short