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 ex

Answer 1

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 2

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 3

Just return session.Linq<T>()

Answer 4

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 5

I can see two possible solutions here:

1. Expose IEnumerable and use .AsQueryable() when needed

   // Repository
   public IEnumerable<Person> GetAll() {
       return _dbContext.People.AsQueryable();
   }
   
   // Usage
   public Person GetByPhone(string phoneNumber) {
       var queryablePeople = _personRepository.GetAll().AsQueryable();
       return queryablePeople.FirstOrDefault(perspn => person.Phone == phoneNumber);
   }
   

2. Accept expression in Repository method

   // Repository
   public IEnumerable<Person> GetPeople(Expression<Func<Person, bool>> filter) {
       return _dbContext.People.Where(filter);
   }
   
   // Usage
   public Person GetByPhone(string phoneNumber) {
       return _personRepository.GetPeople(person => person.Phone == phoneNumber).FirstOrDefault();
   }
   

Note: Not any expression filter can be translated to SQL Query by Entity Framework