Map content in an EntityModel is not properly unwrapped

[dawi]

@JsonUnwrapped is ignored if EntityModel.content is a Map.

This seems to be a Jackson issue (FasterXML/jackson-databind#171) but it would be nice if the user would not have to figure this out the hard way.

Some thoughts

1. It would be great if EntityModel could be fixed

But I am afraid that there is no simple solution to this issue.
See @odrotbohm comments in this thread: FasterXML/jackson-databind#171 (comment)

2. Validation

There already is a validation that checks if the content is a Collection.
Maybe the validation can also check if the content is a Map:

Assert.notNull(content, "Content must not be null!");
Assert.isTrue(!(content instanceof Collection), "Content must not be a collection! Use Resources instead!");
Assert.isTrue(!(content instanceof Map), "Content must not be a map! Use Resources instead!");

3. MapModel

It would be great to have a MapModel provided by Spring HATEOAS.

public class MapModel extends RepresentationModel<MapModel> {

    private final Map<String, Object> content;

    public MapModel(Map<String, Object> content) {
        this.content = content;
    }

    @JsonAnyGetter
    public Map<String, Object> getContent() {
        return content;
    }
}

[odrotbohm]

As indicated in the linked ticket, there is a POC for this that allows us to refrain from adding yet another representation model base class just to work around a (current) limitation of Jackson.

It's all in the works, I just haven't gotten to finish it given all the other fixes I had on my table the last couple of days.

[odrotbohm]

That's in place now. Also backported in the context of #1158.

[abinet]

Hi all,
I'm currently have an issue with the latest changes in EntityModel<Map<String, Object>>
It seems now we are getting the map's content duplicated on serialization.

	@Test
	public void testSerialization() throws JsonProcessingException {
		final HashMap map = new HashMap();
		map.put("field1", "value1");
		final String serialized = new ObjectMapper().writeValueAsString(new EntityModel<>(map));

		System.out.println(serialized);
	}

{"content":{"field1":"value1"},"links":[],"field1":"value1"}

Is it how it is supposed to be?

spring-hateoas:1.4.0.RELEASE
spring-boot:2.2.6.RELEASE
com.fasterxml.jackson.core:jackson-databind:2.10.3

[mika91]

same here (spring-hateoas:1.1.0, jackson:2.11.0, spring-boot:2.3.1)

EDIT: just checked the source code, unit tests behaves simillary