Hi,

In this article I’ll shows a pretty useful way to build simple LinqToSql Queries with reusable IQueryable<T> Extension Methods.

Assuming a LinqToSql DataContext which contains a single Class named “User”

Now we want to Query a User by it’s Email Address.

Using Standard Linq Query we do the following in our UserController Class :

public User GetByEmail(String email)
{
    return Context.Users.Where(p => p.Email == email).SingleOrDefault();
}

This works fine but we can make this Where clause Reusable for further usages.

So we create a Extension Methods Class called UserExtensions :

public static class UserExtensions
{
    public static IQueryable<User> WithEmail(this IQueryable<User> q, String email)
    {
        return q.Where(p => p.Email == email);
    }
}

We can now modify our GetByEmail method and use our Extension method :

public User GetByEmail(String email)
{
    return Context.Users.WithEmail(email).SingleOrDefault();
}

This is now clear and Reusable !

Some other Examples :

public Boolean IsValidUser(String email, String password)
{
    var q = Context.Users.WithEmail(email).WithPassword(password);
    return q.SingleOrDefault() != null;
}

public Boolean UserExists(String email)
{
    return Context.Users.WithEmail(email).SingleOrDefault() != null;
}

So here is how to take Advantage of the IQueryable Interface with Extension Methods.

Hope this help’s!