Expose a repository as an IQueryable

Question

I'd like to expose a Repository as an 'IQueryable' type.

The repository uses Linq to NHibernate to communicate with the database.

Can anyone point me at an example implementation?

For example, what would the corresponding 'GetEnumerator()' implementation on my repository look like?

Edit:

Would something like this be appropriate?

public class MyTypeRepository : IEnumerable<MyType>
{        
    IEnumerator<MyType> IEnumerable<MyType>.GetEnumerator()
    {
        return Session.Linq<MyType>().GetEnumerator();
    }


    IEnumerator IEnumerable.GetEnumerator()
    {
        return ((IEnumerable<MyType>)this).GetEnumerator();
    }

}

Answer 1

This is a bad design.

An IQueryable is a question (lookup "query" in a dictionary). It's how you ask for data. It's what you should be giving to the Repository.

A Repository should be returning answers -- the data itself.

If the Repository is returning a IQueryable, you've pretty much negated the need for the Repository.

Answer 2

I think a Repository can give you 1 or more IQueryables/IEnumerables, but not : a Repository is an IQueryable.

It could look like:

 public interface IPersonRepository
 {
    IEnumerable<Person> GetAllPersons();
    void AddPerson(Person person);

    // more...
 }

You could return IQeryable<Person> from GetAllPerson() but that may not be an improvement. IEnumerable is simpler, less coupling.

Answer 3

Lots of opinions of this one, but Ayende (Oren Eini) seems to think IQueryable is ok to return and articulates his point rather well.

Answer 4

Just return session.Linq<T>()