Spring Boot - MongoDB - Inheritance

Question

I'm running into something odd with inheritance and mongodbrepositories.

I have the following:

`

@Document
public class Base {
    public String fieldA;
}

public class Derived extends Base {
    public String fieldB;
}

public interface DerivedRepository extends MongoRepository<Base, String> {
    List<Derived> findByFieldA(String fieldA);
}

`

When inserting i get

Inserting DBObject containing fields: [_class, _id, fieldA, fieldB ] in collection: base

When i do findByFieldA('some value') on the repository i get the following:

find using query: { "fieldA" : "some value" } fields: null for class: class Derived in collection: derived

Any idea what is going on here? And how can I fix this, either by saving it to the proper derived collection or by querying from the base collection.

Regards,

Answer 1

First, I would make Derived class as document since the parent is going to be shared among many implementations.

public class Base {
    public String fieldA;
}

@Document
public class Derived extends Base {
    public String fieldB;

    @Override
    public String toString() {
        return "{fieldA: " + getFieldA() + ", fieldB: " + fieldB + "}";
    }
}

Second, change the repository specification with the type of document (class marked as @Document) as:

public interface DerivedRepository extends MongoRepository<Derived, String> {
    List<Derived> findByFieldA(String fieldA);
    List<Derived> findByFieldB(String fieldB);
}

I added extra method findByFieldB(String fieldB) to explain more.

With these changes, you should be able to query either with fieldA or fieldB as below:

public class SpringBootMongoApplication {
    @Autowired
    private DerivedRepository derivedRepository;

    public void testMethod() throws Exception {
        Derived derived1 = new Derived();
        derived1.setFieldB("fieldB1");
        derived1.setFieldA("fieldA1");

        Derived derived2 = new Derived();
        derived2.setFieldB("fieldB2");
        derived2.setFieldA("fieldA2");
        this.derivedRepository.save(Arrays.asList(derived1, derived2));

        List<Derived> deriveds = this.derivedRepository.findByFieldA("fieldA1");
        System.out.println(deriveds);

        List<Derived> deriveds1 = this.derivedRepository.findByFieldB("fieldB2");
        System.out.println(deriveds1);
    }
}

The output should be:

[{fieldA: fieldA1, fieldB: fieldB1}]
[{fieldA: fieldA2, fieldB: fieldB2}]

You can also verify the object persisted and their types with mongo query as below:

I have created an Spring Boot sample app which you can find in Github.