LINQ to SQL: On load processing of lazy loaded associations

Question

If I have an object that lazy loads an association with very large objects, is there a way I can do processing at the time the lazy load occurs? I thought I could use AssociateWith or LoadWith from DataLoadOptions, but there are very, very specific restrictions on what you can do in those. Basically I need to be notified when an EntitySet<> decides it's time to load the associated object, so I can catch that event and do some processing on the loaded object. I don't want to simply walk through the EntitySet when I load the parent object, because that will force all the lazy loaded items to load (defeating the purpose of lazy loading entirely).

Answer 1

Subscribe to the ListChanged Event

EntitySet<T> exposes an event called ListChanged which you can use to detect if an item is being added. Evaluate the ListChangedType property of the ListChangedEventArgs. Here's a link to the values available in the ListChangedType enum.

There is no danger of forcing the load to execute as long as you avoid requesting the enumerator.

http://msdn.microsoft.com/en-us/library/system.componentmodel.listchangedtype.aspx

Answer 2

I don't see any extensibility points for this available; the only thing I can see is in the FK entity there is a Created method on each individual object that gets fired from the constructor...

So the constructor calls created, and personally, I'm not 100% sure that the entity set loading creates each individual object at that time, and fires the event...

HTH.

Answer 3

There are a bunch of built in extensibility methods to the datacontext and data classes generated by Linq2SQL.

http://msdn.microsoft.com/en-us/library/bb882671.aspx

http://csainty.blogspot.com/2008/01/linq-to-sql-extending-data-classes.html

Either of these may be able to serve the purpose you need.