Can I define properties in partial classes, then mark them with attributes in another partial class?

Question

Is there a way I can have a generated code file like so:

public partial class A {
public string a {get; set;}
}

and then in another file:

public partial class A {
[Attribute("etc")]
public string a {get; set;}
}

So that I can have a class generated from the database and then use a non-generated file to mark it up?

Answer 1

If I understand your question correctly, then the answer is yes. I use this when I have a MVC project using LINQ2SQL and I write "buddy classes" to implement field validation code in the partial class.

public class foo
{
    public string FirstName { get; set; }
}

public partial class foo
{
    [Required(ErrorMessage = "This is a required field.")]
    public string FirstName { get; set; }
}

Answer 2

Not as such; the compiler will complain that the member is defined in multiple parts. However, as the use of custom attributes is reflective in nature, you could define a "metadata" class and use it to contain decorators.

public class A
{
   public string MyString;
}

public class AMeta
{
   [TheAttribute("etc")]
   public object MyString;
}

...

var myA = new A();
var metaType = Type.GetType(myA.GetType().Name + "Meta");
var attributesOfMyString = metaType.GetMember("MyString").GetCustomAttributes();

Answer 3

I've seen something like this done in an article by Scott Guthrie (near the end of it) - didn't try it myself, though.
http://weblogs.asp.net/scottgu/archive/2010/01/15/asp-net-mvc-2-model-validation.aspx