Question

I am using Datanucleus/JDO to persist objects in a MongoDB DB.
I try to persist an object containing a Map, which value type is an abstract class.

When I try to persist an instance of that object, fields of the abstract class are persisted, but not those of the child class.

Below is some code as an example.

Zoo.java

    @PersistenceCapable
    public class Zoo {

            @Persistent
            private String fieldZoo;
            @Persistent
            private Map<String, Animal> mapStringAnimal;

            // etc... basic constructor...
    }

Animal.java

    @PersistenceCapable(embeddedOnly = "true")
    public abstract class Animal {

            @Persistent
            private String  fieldAnimal;

    }

Dog.java

    @PersistenceCapable(embeddedOnly = "true")
    public class Dog extends Animal {

            @Persistent
            private String  fieldDog;

    }

Test.java

    public static void main(String[] args) {
            Map<String, Animal> mapStringAnimal = new HashMap<String, Animal>();
            Dog dog = new Dog("valueFieldAnimal", "valueFieldDog");
            mapStringAnimal.put("dogKey", dog);
            Zoo zoo = new Zoo("valueFieldZoo", mapStringAnimal);

            Properties properties = new Properties();
            properties.setProperty("javax.jdo.PersistenceManagerFactoryClass", "org.datanucleus.api.jdo.JDOPersistenceManagerFactory");
            properties.setProperty("javax.jdo.option.ConnectionURL", "mongodb:/dbtest");
            properties.setProperty("javax.jdo.option.Mapping", "mongodb");
            properties.setProperty("datanucleus.autoCreateSchema", "true");
            PersistenceManagerFactory pmf = JDOHelper.getPersistenceManagerFactory(properties);
            PersistenceManager pm = pmf.getPersistenceManager();

            pm.makePersistent(zoo);
            pm.close();
    }

And when I look at MongoDB:

    > db.Zoo.find().pretty();

    {
            "_id" : ObjectId("50d2f5f7e4b0cae285990b2d"),
            "fieldZoo" : "valueFieldZoo",
            "mapStringAnimal" : [
                    {
                            "key" : "dogKey",
                            "value" : {
                                    "fieldAnimal" : "valueFieldAnimal"
                            }
                    }
            ]
    }

Answer 1

Yes, but DataNucleus doesn’t support embedded inherited Map keys/values. It does support embedded inherited Collection elements (part of not-yet-released JDO3.1), but not the equivalent for Maps. Obviously the code is open source and anyone could dive in and contribute it (once you’ve added a discriminator to “Animal” of course).