Question

I have been thinking generally about exception handling.

What would be the best practice for implementing a method that gets a User object based on the supplied username parameter. See below.

    /// <summary>
    /// Gets a user.
    /// </summary>
    /// <param name="username">Username</param>
    /// <returns>User instance</returns>
    public Model.User GetUser(string username)
    {
        return Context.Users.SingleOrDefault(u => u.Username.ToLower() == username.ToLower());
    }

if no user exists with that username parameter, would it be better to return a null User object or rather throw a custom exception specifying that the user does not exist.

Answer 1

Throw an exception. Otherwise, your caller, and your caller’s caller, and everyone else will need to check for null, or will need to handle an empty collection.

If this is a general-purpose method, meant to be used in a context where the caller knows he needs to check for null, then I’d do this a bit differently. I would have a private method that returns null if there are no users who match. I would add a caller which uses the “try” pattern:

public bool TryGetUser(string username, out Model.User user)

and also one that simply returns the user, but throws an exception if not found

public Model.User GetUser(string username)