Spring Boot - MongoDB - Inheritance - spring

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.