How to make generic jpa repository? Should I do this? Why?

Question

I am new to stack overflow and working on spring jpa data with hibernate and mysql. I have created One JpaRepository for each entity class. But now I feel that I should use One repository for all entities because In all my repositories has common CRUD operation methods.

1. save()

2. update()

3. delete()

4. findOne()

5. findAll()

Besides of above methods, I have other custom methods also in my applications.

my aim is to implement GenericRepo like,

public interface MyGenericRepo extends JpaRepository<GenericEntity,Integer>
{

}

my entities will be like:

class Place extends GenericEntity
{
    private Event event;
}

class Event extends GenericEntity
{  

}

class Offer extends GenericEntity
{
     private Place place;
}

class User  extends GenericEntity
{
     private Place place;
}

when I call:

    MyGenericRepo myRepo;

    GenericEntity place=new Place();

    myRepo.save(place);

It should save place.

[http://openjpa.apache.org/builds/1.0.2/apache-openjpa-1.0.2/docs/manual/jpa_overview_mapping_inher.html#jpa_overview_mapping_inher_joined][1]

I have referred above link and I found that Jpa Inheritance with Joined and Table-Per-Class strategies are similar to what I am looking for, but these all have certain limitations.So please tell me should I try to implement this generic thing.If I get any demo code then I will be very greatful...

Thanks..

How to make generic jpa repository? Should I do this? Why?

Answer 1

If you want to create your own Repos (and not spring data which does some work for you) your example isn't bad, i am using a similar strategy in one application.

Here a few thoughts to improve the generic way: I've added the ID-information in my basic domain which is implemented by all domain objects:

public interface UniqueIdentifyable<T extends Number> {
    T getId();
    void setId(T id);
}

In the next step i've created a generic CRUDRepo:

public interface CRUDRepository<ID extends Number, T extends UniqueIdentifyable<ID>>{
   ID insert(T entity);
   void delete(T entity);
   ....
} 

And I am using an abstract class for the CRUDRepo:

public abstract class AbstractCRUDRepo<ID extends Number, T extends UniqueIdentifyable<ID>> implements CRUDRepo<ID, T>, {...}

a domain repo api will now look like:

public interface UserRepo extends CRUDRepo<Integer, User > {
   User mySpecificQuery(..);
} 

and finally you can implement your repo via:

public class UserRepoImpl extends AbstractCRUDRepo<Integer, User > implements UserRepo {
   public User mySpecificQuery(..){..}
}