Access Business Object Metadata

• Oct 19, 2023
• 3 minutes to read

This topic explains how the Types Info Subsystem can be used in your applications.

Business class metadata can be accessed via the static Instance property of the XafTypesInfo class. This property returns an ITypesInfo object, which represents metadata on all business classes used in an XAF application. To get metadata on a particular entity, perform the following steps:

1. Access the XafTypesInfo.Instance property to get an ITypesInfo object.

   XafTypesInfo.Instance

2. To get metadata on a business class, use the ITypesInfo.FindTypeInfo method.

   XafTypesInfo.Instance.FindTypeInfo(ObjectType)

   This method returns an ITypeInfo object.

3. To get metadata on a business class member, use the ITypeInfo object’s ITypeInfo.FindMember method.

   XafTypesInfo.Instance.FindTypeInfo(ObjectType).FindMember(PropertyName)

   This method returns an IMemberInfo object.

4. To get specific information, use the properties of the ITypeInfo or IMemberInfo object. The ITypeInfo object provides information about a type, and the IMemberInfo object provides information about a member.

   XafTypesInfo.Instance.FindTypeInfo(ObjectType).IsAbstract

   XafTypesInfo.Instance.FindTypeInfo(ObjectType).FindMember(PropertyName).IsList

The types info interfaces declare many properties and methods that supply metadata. To learn about the metadata the types info subsystem supplies, refer to the member list of each interface.

In addition to the XafTypesInfo class, many XAF classes supply metadata associated with them. For instance, Property Collection Sources have the PropertyCollectionSource.MemberInfo property, which supplies metadata on a property represented by the Collection Source. Another example is a View that exposes the ObjectView.ObjectTypeInfo property, supplying metadata on the type of represented objects.

Below is an example on how to utilize the metadata supplied by the types info subsystem. In the code snippet, a View Controller checks whether or not a business class has a custom MyAttribute attribute applied. If the attribute is applied, then the custom code is executed when the Controller is activated.

C#

//...
[AttributeUsage(AttributeTargets.Class, Inherited = false)]
public class MyCustomAttribute : Attribute { }

[MyCustomAttribute]
public class DemoContact : BaseObject {
//...
}

//...
public partial class MyViewController : ViewController {
    //...
    private void MyViewController_Activated(object sender, EventArgs e) {
        if (View.ObjectTypeInfo.FindAttribute<MyCustomAttribute>() != null) {
            // Place your code here.
        }
    }
}

VB.NET

'...
<AttributeUsage(AttributeTargets.Class, Inherited := False)> _
Public Class MyCustomAttribute
    Inherits Attribute
End Class

<MyCustomAttribute> _
Public Class DemoContact
    Inherits BaseObject
'...
End Class

'...
Partial Public Class MyViewController
    Inherits ViewController
    '...
    Private Sub MyViewController_Activated(ByVal sender As Object, ByVal e As EventArgs)
        If View.ObjectTypeInfo.FindAttribute(Of MyCustomAttribute)() IsNot Nothing Then
            ' Place your code here.
        End If
    End Sub
End Class

Note

In this code, DemoContact is an XPO class, but it can be an Entity Framework entity class as well. The MyViewController Controller operates in the same way in all of these cases.

Another situation when you may need to access the types info subsystem is when you need to add an attribute to a class or member from an external class library. Refer to the How to customize a Business Model at runtime example for details.