使用存储库模式时如何返回可枚举的对象？

Question

I am working on a simple WCF application and I am having trouble with properly setting up the Repository pattern. The communication pattern of the application is roughly as shown here .

I am concerned with the part that says Admin Console Mode . In this mode, the admin has access to some admin features like adding users and viewing existing users etc.

Abstract contract of one of the entities, Users , needed for this mode, is as follows:

public interface IUserRepository
{
    byte AddUser(string _loginname, string _loginpass);
    Users ShowAllUsers();
}

The concrete implementation of this repository:

public class UserRepository : IUserRepository
{
    public UserRepository(string connectionString)
    {
        _connectionString = connectionString;
    }

    public byte AddUser(string _loginname, string _loginpass)
    {
        . . .
    }

    public Users ShowAllUsers()
    {
        string query = "select login_name,created_time from users";

        using(SqlConnection conn = new SqlConnection(_connectionString))
        {
            using(SqlCommand cmd = new SqlCommand(query, conn))
            {                    
                conn.Open();

                using(var reader = cmd.ExecuteReader())
                {
                    if(!reader.Read())
                        return null;

                    return new Users
                    {
                        Login_Name = reader.GetString(reader.GetOrdinal("login_name")),
                        Login_Pass = reader.GetString(reader.GetOrdinal("login_pass")),
                        Created_Time = reader.GetDateTime(reader.GetOrdinal("created_time")),
                    };
                }
            }
        }
    }
}

From the Host layer, How do I access the list of Users objects returned from the ShowAllUsers method? I tried this way:

public void ShowUsers()
{
    Users user = _repo.ShowAllUsers();

    Console.WriteLine("Name\tCreated Time");

    foreach(Users u in user)
    {
        Console.WriteLine("{0}\t{1}",u.Login_Name,u.Created_Time);
    }
}

From what I understand, this does not work obviously since the Users object is not an enumerable object. How do I modify the Users entity and the repository contract and the repository implementation so that the Users object is returned to be displayed on the screen?

Users.cs
UserRepository.cs
IUserRepository.cs

Answer 1

Entity:

// note the singular form, it makes much more sense for me, as far as the object represents a single entity (user)
// also not an interface, optionally
public class User : IUser
{
}

Repository:

public class UserRepository : IUserRepository
{
    public IEnumerable<IUser> ShowAllUsers()
    {
        ...
        while (reader.Read())
        {
             yield return new User
             {
                 ...
             };
        }
    }
}

I recommend yo use interfaces everywhere, because if you will want to switch from ADO.NET query to an ORM, you will need to rewrite much less code.

---

Usage:

foreach (User u in users)
{
    Console.WriteLine("{0} created on {1}", u.Login, u.CreationTime);
}