java - Selectively expand associations in Spring Data Rest response

Question

I have a standard Spring data JPA and Spring data Rest setup which, correctly, returns associations as links to the correct resources.

{
    "id": 1,
    "version": 2,
    "date": "2011-11-22",
    "description": "XPTO",
    "_links": {
        "self": {
            "href": "http://localhost:8000/api/domain/1"
        },
        "otherDomain": {
            "href": "http://localhost:8000/api/domain/1/otherDomain"
        }
    }
}   

However in some requests i would like to have the association to the "otherDomain" expanded (so the client does not have to do N+1 requests to get the full data).

Is it possible to configure Spring Data Rest to handle the response in this way?

Answer 1

The default responses will have to stay the same to make sure the payloads for PUT requests are symmetric to the ones GETs return. However, Spring Data REST introduces a feature called projections (see the JIRA ticket for details) that works as follows:

You create a dedicated interface and add all properties that you want to include in the response:

public interface MyProjection {

  String getMyProperty();

  MyRelatedObject getOtherDomain();
}

You can either

• annotate the interface using @Projection and place it in the very same package as the domain type or a subpackage of it
• or you manually register the projection using the RepositoryRestConfiguration and call projectionConfiguration().addProjection(…) manually (by extending RepositoryRestMvcConfiguration and overriding configureRepositoryRestConfiguration(…)).

This will cause the resources exposed for the domain type to accept a projection parameter (name also configurable ProjectionConfiguration) with the name of the projection. If given, we will skip the default rendering (which includes rendering links to related entities instead of embedding them) and let Jackson render a proxy backing the given interface.

An example of that can also be found in the Spring RESTBucks project. See the OrderProjection for the interface definition.