Databases Reference
In-Depth Information
private abstract class Metadata
{
[Required]
public object ProductName { get; set; }
}
}
From a validation standpoint, placing any .NET attributes on fields or properties of the
metadata class has the same effect as placing them on their counterparts in the real class.
Only the name of the field or property matters from the matching prospective, so the
metadata class could declare
ProductName
as a field of type
object
even though it is a
property of type
string
in the real class. However, if the metadata class has a property or
field that
does not
have a property with the same name in the real class, you get an
InvalidOperationException
whenever you try to access its attributes for the first time,
such as when passing an object to the
ValidateObject
method of the
Validator
class.
NOTE
The compiler does not issue an error when a partial class contains only one definition,
which makes it easy to create partial classes that do not match their generated coun-
terparts. You could mistype the name of the class itself or place it in a different name-
space. If you notice that additional metadata attributes you applied in the metadata
type seem to have no effect on the Dynamic Data pages, double-check that all partial
class definitions match, or better yet, create an automated test to verify it, as you learn
about later in this chapter.
NOTE
Notice that the Metadata class was made
abstract
,
private
, and
nested
intentionally.
The metadata classes are never instantiated by the application. In addition to violating
object-oriented design principles, making metadata classes
public
unnecessarily
pollutes the IntelliSense information in Visual Studio. This becomes more and more
noticeable as the number of metadata classes in your application grows.
To eliminate the confusion of having a different type specified for a property as well as to
avoid mistakes caused by incorrect property names in the metadata classes, you can use
metadata
interfaces
instead. Here is the same partial
Product
class extended with a meta-
data interface instead of a metadata class:
using System.ComponentModel.DataAnnotations;
internal interface IProduct
{
[Required]
string ProductName { get; set; }
}
