@JsonUnwrapped ignored with (embedded) CollectionModel and HAL Forms

[toedter]

To create REST resources with a list of embedded resources I use a pattern like

@JsonUnwrapped
CollectionModel<EntityModel<Movie>> movies;

As an example:

@Data
public class DirectorRepresentationModel extends RepresentationModel {
    private long id = 1;
    private String name = "Steven Spielberg";

    @JsonUnwrapped
    CollectionModel<EntityModel<Movie>> movies;

    public DirectorRepresentationModel() {
        Movie movie1 = new Movie();
        movie1.setId("1");
        movie1.setTitle("ET");

        Movie movie2 = new Movie();
        movie2.setId("2");
        movie2.setTitle("Jaws");

        EntityModel<Movie> p1 = new EntityModel<>(movie1);
        EntityModel<Movie> p2 = new EntityModel<>(movie2);

        movies = new CollectionModel<>(Arrays.asList(p1, p2));
    }
}

When setting the hypermedia configuration to HAL, it is rendered as I would expect:

{
  id: 1,
  name: "Steven Spielberg",
  _embedded: {
    movieList: [
      {
          id: "1",
          title: "ET"
      },
      {
           id: "2",
           title: "Jaws"
      }
     ]
   }
}

But when setting the hypermedia configuration to HAL_FORMS, the @JsonUnwrapped does not apply:

{
  id: 1,
  name: "Steven Spielberg",
  movies: {
    _embedded: {
       movieList: [
         {
             id: "1",
             title: "ET"
         },
         {
              id: "2",
              title: "Jaws"
         }
        ]
     }
  }
}

IMHO HAL_FORMS should render this exactly like HAL does.

[gregturn]

HAL-FORMS serialization copies the model’s data into a set of classes aimed at signaling Jackson on how to render. HAL just serializes the Model directly.

I had not anticipated mixing model types like you did. Should make the perfect test case!

Additionally this information is useful for #864.

[toedter]

Hmm, when using the latest snapshot (March 31.), HAL_FORMS would not render any property in a derived RepresentationModel anymore (at least in my tests). When setting the hypermedia configuration to HAL_FORMS, the above example is now rendered as:

{
  id: 1,
  name: "Steven Spielberg"
}

@gregturn: HAL-FORMS serialization copies the model’s data into a set of classes aimed at signaling Jackson on how to render. HAL just serializes the Model directly.

IMHO it is very important that the HAL_FORMS implementation renders RepresentationModels that don't use any affordances (which will be mapped on HAL Forms _templates) the very same way that the HAL implementation renders them.

Today, the only way I found to get _embedded rendered in a non-collection model with @EnableHypermediaSupport(type = HypermediaType.HAL_FORMS) is to put a _embedded JSON property in the domain model, which is exactly what we want to avoid :)

Or is there a better way using only representation models to render a result with HAL Forms like:

{
  id: 1,
  name: "Steven Spielberg",
  _links: {
    self: {
      href: "http://localhost:8080/directors/4"
    }
  },
  _embedded: {
    movies: [
      {
          id: "1",
          title: "ET"
          _links: {
             self: {
              href: "http://localhost:8080/movies/1"
            }
          }
      },
      {
           id: "2",
           title: "Jaws"
          _links: {
             self: {
              href: "http://localhost:8080/movies/2"
            }
          }
      }
     ]
   }
}

[gregturn]

IMHO it is very important that the HAL_FORMS implementation renders RepresentationModels that don't use any affordances (which will be mapped on HAL Forms _templates) the very same way that the HAL implementation renders them.

Agreed.

Thought I had a guess what “fix” broke your solution. Turns out I was wrong. My fix hasn’t been merged to master yet.

The point is, HAL and HAL-FORMS use very different serialization strategies so the solution isn’t straight forward.

To be honest I’d like to rewrite HAL so that it’s just like HAL-FORMS offering better consistency in design.

We could almost use a TCK...a batch of tests that exercise a wide range of model combinations with expected outcomes.

[gregturn]

Related to #970.

[toedter]

A workaround for HAL_FORMS rendering representation model properties is to always use the pattern

public class MyModel extends RepresentationModel<MyModel>

Then all the attributes in MyModel are treated as content.
But still: @JsonUnwrapped would not work for

@JsonUnwrapped
CollectionModel<EntityModel<Movie>> movies;