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Generated JSON Schema incorrect for @JsonIdentityReference(alwaysAsId = true)

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
42/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Stale
Tech stack
java
Domain
backend-api-design, tooling

Research direction

Start at JsonSchemaGenerator.generateJsonSchema(ManagingObject.class) and trace how @JsonIdentityReference(alwaysAsId = true) is handled for ReferencingObject.referencedObject. Reproduce the mismatch with the three classes and compare the generated schema with the shown serialized JSON. Done means the schema accepts the scalar identity value emitted for that property.

Written by the indexing model from the issue text.

Description

Hi,

I am trying to create a JSON representation of a datamodel and want to use a JSON Schema to validate the contents. When using the JSON Schema generated by the jsonSchema module I run into trouble when I have a property which is an identify reference (@JsonIdentityReference(alwaysAsId = true)).

For example when we have three classes: ManagingObject (which manages everything), ReferencedObject (the object which is managed by ManagingObject) and ReferencingObject (an object which references to ReferencedObject and is also managed by ManagingObject):

public class ManagingObject {
    @JsonManagedReference
    public Vector<ReferencedObject> referencedObjects;
    
    @JsonManagedReference
    public ReferencingObject referencingObject;
    
    public ManagingObject() {
        referencedObjects = new Vector<ReferencedObject>();
    }
}

@JsonIdentityInfo(property="id", generator=ObjectIdGenerators.PropertyGenerator.class)
public class ReferencedObject {
    public UUID id;
    
    public String someOtherProperty;
    
    public ReferencedObject() {
        id = UUID.randomUUID();
    }
}

public class ReferencingObject {
    @JsonIdentityReference(alwaysAsId = true)
    public ReferencedObject referencedObject;
}

When I then create a sample JSON using the following code:

// Create an example JSON.
ObjectMapper objectMapper = new ObjectMapper();
ManagingObject mo = new ManagingObject();
// Create the ReferencedObject and add it to the ManagingObject collection.
ReferencedObject ro = new ReferencedObject();
ro.someOtherProperty = "Something";
mo.referencedObjects.add(ro);
// Create the ReferencingObject and set its referencedObject and also add a reference in the ManagingObject to it.
ReferencingObject rco = new ReferencingObject();
rco.referencedObject = ro;
mo.referencingObject = rco;
// Create a JSON representation of the ManagingObject.
System.out.println(objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(mo));

Then the output is what I would expect (in the ReferencingObject it points directly to the id and doesn't include the full referencedObject):

{
  "referencedObjects" : [ {
    "id" : "de0fb81e-014d-480a-8b65-01ce2daf719f",
    "someOtherProperty" : "Something"
  } ],
  "referencingObject" : {
    "referencedObject" : "de0fb81e-014d-480a-8b65-01ce2daf719f"
  }
}

But when I then generate a JSON Schema using the following code:

// Create the JSON Schema.
ObjectMapper objectMapper = new ObjectMapper();
JsonSchemaGenerator jsonSchemaGenerator = new JsonSchemaGenerator(objectMapper);
JsonNode jsonSchema = jsonSchemaGenerator.generateJsonSchema(ManagingObject.class);
System.out.println(objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(jsonSchema));

Then the output is not what I would expect for the referencedObject in ReferencingObject (unless I misunderstand):

{
  "$schema" : "http://json-schema.org/draft-04/schema#",
  "title" : "Managing Object",
  "type" : "object",
  "additionalProperties" : false,
  "properties" : {
    "referencedObjects" : {
      "type" : "array",
      "items" : {
        "$ref" : "#/definitions/ReferencedObject"
      }
    },
    "referencingObject" : {
      "$ref" : "#/definitions/ReferencingObject"
    }
  },
  "definitions" : {
    "ReferencedObject" : {
      "type" : "object",
      "additionalProperties" : false,
      "properties" : {
        "id" : {
          "type" : "string"
        },
        "someOtherProperty" : {
          "type" : "string"
        }
      }
    },
    "ReferencingObject" : {
      "type" : "object",
      "additionalProperties" : false,
      "properties" : {
        "referencedObject" : {
          "$ref" : "#/definitions/ReferencedObject"
        }
      }
    }
  }
}

When I look at the ReferencingObject definition of the schema I see a JSON Pointer to the ReferencedObject definition for the 'referencedObject' property, but in the example JSON the id is directly mapped (not a full JSON representation of the ReferencedObject). So the JSON produced is not valid according the JSON Schema on the same object model.

Am I doing something wrong or weird here? Or should the JSON Schema look a bit different for the properties which are marked with the annotation @JsonIdentityReference(alwaysAsId = true) ?

Dominant language
Java
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