Question

I have such database structure (1 – one, 0 – many)

Product 1->0 Orders 0->1 Users

I need to find all users for specified product, I have started writing linq query but don’t know how to finish it.

public IQueryable<User> GetUsers(int productId)
{            
  return _db.Products.First(p => p.Id == productId)....
}

Answer 1

First things first, the First method will only return the first item that meets your criteria, and since you want to return an IQueryable of Users, this is probably not what you want.

Second, I think the easiest way to get started with Linq-to-SQL is to use query notation, especially when you’re dealing with joins, which don’t look too pretty when using lambda expressions.

public IQueryable<User> GetUsers(int productId)
{
    return from p in _db.Products
           join o in _db.Orders on p.Id equals o.productId
           join u in _db.Users on o.userId equals u.userId
           where p.productId == productId
           select u;
}