Equivalent of IQueryable in Spring Data

Question

I'm used to .Net and LINQtoEntities, especially the IQueryable part which allows to carry a request through different functions before fetching the results.

Does anything like this exist in spring data ? Or any other java ORM ?

Basic example of what I'd like to be able to do :

private IQueryable<Todo> GetAll(){
  context.Todos.Where(t => !t.Deleted);
}

public IEnumerable<Todo> GetDoneTodos(){
  GetAll().Where(t => t.Done).ToList();
}

Answer 1

You can use Spring Data's QueryDSL integration. Basically, you extend the QueryDslPredicateExecutor in your repository interface and it add a findAll method that gets a QueryDSL Predicate and filter all the results based on that Predicate. Suppose we have domain object, say Greeting, then we'd have repository like this:

public interface GreetingRepository extends QueryDslPredicateExecutor<Greeting> {}

Then you can use generated QModels generated by QueryDSL to create a Predicate and pass it to our greetingRepository. Suppose we're going to filter all the Greetings by one specific user:

Predicate filterByUser = greeting.user.eq(someUser);
greetingRepository.findAll(filterByUser);

greeting is a metamodel generated by QueryDSL based on our Greeting model.

Note 1: You can see how you can integrate Spring Data and QueryDSL here and see more examples for QueryDSL's Predicates here.

Note 2: QueryDslPredicateExecutor also provides findOne(Predicate predicate), count(Predicate predicate) and exists(Predicate predicate) methods which are useful and self-explanatory, of course.

Note 3: You can achieve almost the same thing with Specifications but in my opnion QueryDSL has more elegant and readable Predicates.