What is the return type of my linq query?

Question

I have two tables A & B. I can fire Linq queries & get required data for individual tables. As i know what each of the tables will return as shown in example. But,

Answer 1

The value you generate is called Anonymous Type and you can return it unless you return object like:

private object GetJoinAAndB()
{
    var query = from a in objA
                join b in objB
                on a.ID equals b.AID
                select new { a.ID, a.Name, b.Address };
    return query.ToList();
}

There are two good solutions:
1. is to generate a class to match the output and generate it like Kobi solution
2. if you are using .net 4 you can return a dynamic type like

private dynamic GetJoinAAndB()
{
    var query = from a in objA
                join b in objB
                on a.ID equals b.AID
                select new { a.ID, a.Name, b.Address };
    return query.ToList();
}

then you can use it later. You can search the internet about the advantage of using dynamic keyword.

Answer 2

As you have created an anonymous(Anonymous types are generated by the compiler, so we cannot know the type name in our codes) class so that you can not return it.Create a separate class with three properties Id,Name and Address then returned it.

  public class Contact
        {
            public int Id { get; set; }
            public string Name { get; set; }
            public string Address { get; set; }

        }

 private IList<Contact> GetJoinAAndB()
    {
        var query = from a in objA
                    join b in objB
                    on a.ID equals b.AID
                    select new Contact{ a.ID, a.Name, b.Address };
        return query.ToList();
    }

Answer 3

Like Kobi said.

If you do not want to create a class specifically for this case, you can use a Tuple. Only supported .Net 4 though.

Answer 4

You've created an anonymous class - you can't really return it. A simple solution is to add a class to represent your type.

For example:

public class UserWithAddress
{
    public UserWithAddress(int id, string name, string address)
    {
        ID = id;
        Name = name;
        Address = address;
    }

    // you may have your own types here
    public int ID { get; set; }
    public String Name { get; set; }
    public String Address { get; set; }
}

And then:

private IList<UserWithAddress> GetJoinAAndB()
{
    var query = from a in objA
                join b in objB
                on a.ID equals b.AID
                select new UserWithAddress(a.ID, a.Name, b.Address);
    return query.ToList();
}