Question

I am writing my first C# application, which in this case is just a “learning exercise” This example is a simplified block of code that I have used many times in VB.Net so I know that it works correctly. This is what the VB code looks like.

Public Class User
    Private Const CN_LoginId As String = "Login"
    Private Const CN_Password As String = "Password"
    Private _password As String

    Public Property Password() As String
        Get
            Return _password
        End Get
        Set(ByVal value As String)
            _password = value
        End Set
    End Property

    Public Shared Function Create(ByVal Login As String) As User
        Dim usr = New User()

        Using dt As DataTable = DAC.ExecuteDataTable("usp_PasswordSelect", _
            DAC.Parameter(CN_LoginId, Login))
            With dt.Rows(0)
                usr.Password = CStr(.Item(CN_Password))
            End With
        End Using

        Return usr
    End Function
End Class

So in C# I have tried converting it by hand and by using Telerik’s online conversion utility, which is what I am posting below because I am assuming that it is closer to the right answer then what I did myself.

public class User
{
    private const string CN_LoginId = "Login";
    private const string CN_Password = "Password";
    private string _password;
    public string Password
    {
        get { return _password; }
        set { _password = value; }
    }

    public static User Create(string Login)
    {
        object usr = new User();

        using (DataTable dt = DAC.ExecuteDataTable("usp_PasswordSelect", 
            DAC.Parameter(CN_LoginId, Login)))
        {
            {
                usr.Password = Convert.ToString(dt.Rows(0).Item(CN_Password));
            }
        }

        return usr;
    }

}

The first error I get is on this line usr.Password = Convert.ToString(dt.Rows(0).Item(CN_Password));. The error is “Error 1 ‘object’ does not contain a definition for ‘Password’ and no extension method ‘Password’ accepting a first argument of type ‘object’ could be found (are you missing a using directive or an assembly reference?)

At this point I am assuming the second error will go away when I fix the first one. So my question is how do I correctly set the property for this Object using the DataTable in C#?

Answer 1

Here’s how I’d write it:

public class User
{
    private const string CN_LoginId = "Login";
    private const string CN_Password = "Password";

    public string Password { get; set; }

    public static User Create(string Login)
    {
        User usr = new User();
        using (DataTable dt = DAC.ExecuteDataTable("usp_PasswordSelect", 
            DAC.Parameter(CN_LoginId, Login)))
            {
                usr.Password = Convert.ToString(dt.Rows[0][CN_Password]);
            }
        return usr;
    }
}

Some notes:

1. C# accesses arrays using square brackets, not parens. So Rows(0) isn’t correct – it should be Rows[0].
2. I agree with Bernard that you should declare the User object as a User, and not as an object. You’ll lose all visibility into it’s properties. You can also use var, but if you’re learning C#, you may be better off explicitly declaring your variable types. It can make for duplicate declarations (e.g. User u = new User()) but at least you’ll see clearly what types your variables are.
3. You don’t need to access array items using Item…just get it as an element in the row element you’re working with. That’s why I have the double array for dt.Rows[0][CN_Password]. Again, C# uses square brackets, not parens for accessing array elements.
4. This is just a style thing, but I removed your _password field and just used an automatic property for Password. I didn’t see _password being used in your code and thought it would just clutter things up. Automatic properties have a backing field automatically created by the compiler, so you don’t have to keep track of the variable and the property. If you’re using a lot of properties, this can be a big time saver.