I use Spring Data REST with JPA. I have a User entity that has a many to one relationship with another called AccountStatus modeled in a separate RDBMS table. The JSON represent
It really depends if you have an exported repository for AccountState. If you do you can update your account state with a PATCH against /users/{id}:
AccountState
PATCH
/users/{id}
{ "accountState": "http://localhost:8080/accountStates/2" }
So you are using the URI of your account state to reference the resource to assign