The requested page is not available for the requested platform. You are viewing the content for .NET Framework 4.5.2+ platform.

Custom Collection Types

Sometimes it is necessary to derive custom collection types from the standard XPCollection or the XPCollection<T>. The standard types have a special constructor that is used when they must be initialized as relationship collections. This specific collection constructor is relevant in two ways:

  • Be sure that your derived collection type implements it.
  • In relation properties on the "one" side of a one-to-many relationship, or in the properties on both sides of a many-to-many relationship, you must use this constructor to create the collection of your derived type.

So, assuming you had a derived collection class MyCollection<T>:


public class MyCollection<T> : XPCollection<T> {
// ...
public MyCollection(Session session, object theOwner, XPMemberInfo refProperty) :
 base(session, theOwner, refProperty) { }
// ...
}

To use this collection type in a relation property, use the following code:


public class Album : XPObject {
    // ...
}

public class Artist : XPObject {
    // ...
    MyCollection<Album> myCollection;
    [Association("Artist-Albums")]
    public MyCollection<Album> Albums {
        get {
            if (myCollection == null)
                myCollection = new MyCollection<Album>(Session, this,
                    ClassInfo.GetMember("Albums"));
            return myCollection;
        }
    } 
    // ...
} 

The code in the property getter is identical to that in the GetCollection<T> method - but because that method doesn't return our own collection type, we have to replace it.

See Also