Jackson-databind: Deserialize JsonManagedReference on many to many relations

Created on 27 Nov 2018 · 5Comments · Source: FasterXML/jackson-databind

Jackson Version: 2.9.7

Objects with a ManyToMany relationship which is managed by @JsonManagedReference/@JsonBackReference cannot be deserialized. This is easiest to show with an example.

public class JsonReferenceTest {
    class Customer {
        @JsonManagedReference("users")
        public Collection<User> users = new ArrayList<>();

        public String name = "company";
    }

    class User {
        @JsonBackReference("users")
        public Collection<Customer> customers = new ArrayList<>();

        public String name = "user";
    }

    ObjectMapper objectMapper = new ObjectMapper();

    @Test
    public void testDeserialize() throws IOException {
        String customer = "{\"name\":\"asdf\"}";

        objectMapper.readValue(customer, Customer.class);
    }
}

Running the following test results in:

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot handle managed/back reference 'users': back reference type (java.util.Collection) not compatible with managed type (com.widewail.JsonReferenceTest$Customer)
 at [Source: (String)"{"name":"asdf"}"; line: 1, column: 1]

Digging into BeanDeserializerBase it looks like when checking that the back reference type matches the reference type it is not checking the contained type of the collection on the back reference side.

Source