Support for Resources in a Resource to be added to _embedded

[tombee]

After speaking with @olivergierke, we came to the conclusion that there's no way to get a Resources collection added to an _embedded collection in the root of the envelope without using @JsonUnwrapped.

The problem then is that if there are multiple Resources fields, the last field serialized will overwrite the existing _embedded section.

I believe that @olivergierke suggests that a new custom serializer needs to be written to support adding Resources fields to the _embedded section.

[tombee]

After speaking with @olivergierke further, the current recommended approach can be seen in: https://gist.github.com/olivergierke/697aeab8638084b15604

I think it'd be nice to see a more intuitive way of supporting HAL _embedded resources.

[dschulten]

Do I understand correctly that you want to serialize a bean which has several attributes of type Resources? Could you elaborate why you need this? Resources is meant to be the header for a collection, and the collection "normally" represents the content of the resource. You could then post to that collection, delete from it etc. Having multiple Resources in one response is not the intended usage for a Resource, as I see it right now.
HAL defines that _embedded "values are either a Resource Object or an array of Resource Objects". This should be covered by a Resource of Resources which might contain exactly one or multiple items. I'm curious why this is not sufficient in your case :)

[tombee]

A use case might be that when I fetch a resource, let's say we are fetching a shop resource, embedded within the resource I would like to add a list of Staff and a list of Products. My instinct was to create a field Resources and a field Resources and hope that the serializer would figure out that both need to be added to _embedded.

What I actually needed to do was to add a field:

@JsonUnwrapped
Resources<Object> _embedded;

To populate it, I needed to combine the elements of the two lists and provide them to the Resources constructor.

It just feels like there might be room for improvement here perhaps? Maybe a HAL specialised version of ResourceSupport could provide some assistance in embedding resources.

I can close the issue if you guys feel that the API is fine as it is, @olivergierke had asked me to create an issue regarding this.

[odrotbohm]

Was this closed by accident?

[tombee]

Ah I thought it wasn't being addressed, since it's been open for so long without a reply :)

[odrotbohm]

If we finally decide not to implement it, we can still close it. Currently I am just a bit swamped with other work. :)

[gregturn]

Related to #864

[gregturn]

In #864, I am working on a builder that supports:

@GetMapping("/explicit-and-implicit-rels")
RepresentationModel<?> explicitAndImplicitRelations() {

    Staff staff1 = new Staff("Frodo Baggins", "ring bearer");
    Staff staff2 = new Staff("Bilbo Baggins", "burglar");

    Product product1 = new Product("ring of power", 999.99);
    Product product2 = new Product("Saruman's staff", 9.99);

    return ModelBuilder3 //
            .entity(staff1) //
            .entity(staff2) //
            .entity(product1) //
            .entity(product2) //
            .link(Link.of("/people/alan-watts")) //
            .entity(LinkRelation.of("ring bearers"), staff1) //
            .entity(LinkRelation.of("burglars"), staff2) //
            .link(Link.of("/people/frodo-baggins", LinkRelation.of("frodo"))) //
            .build();
}

Yielding...

{
  "_embedded" : {
    "burglars" : {
      "name" : "Bilbo Baggins",
      "role" : "burglar"
    },
    "staffs" : [ {
      "name" : "Frodo Baggins",
      "role" : "ring bearer"
    }, {
      "name" : "Bilbo Baggins",
      "role" : "burglar"
    } ],
    "ring bearers" : {
      "name" : "Frodo Baggins",
      "role" : "ring bearer"
    },
    "products" : [ {
      "name" : "ring of power",
      "price" : 999.99
    }, {
      "name" : "Saruman's staff",
      "price" : 9.99
    } ]
  },
  "_links" : {
    "self" : {
      "href" : "/people/alan-watts"
    },
    "frodo" : {
      "href" : "/people/frodo-baggins"
    }
  }
}