Django Google app engine reference issues
You could also just set a flag, say deleted, on the entity you're deleting, and then leave it in the datastore. This has the advantage of avoiding all referential integrity problems in the first place, but it comes at the cost of two main disadvantages:

All your existing queries need to be changed to deal with entities that have the deleted property set, either by omitting them from the result set or by special casing them somehow.
"Deleted" data stays in the datastore; this can bloat the datastore, and also may not be an option for sensitive information.

This doesn't really solve your problem at all, but I thought I'd mention it for completeness's sake.
I am working on an application on Django and google application engine. In my application I have several models with several ReferenceProperty fields. The issue  is that if any of the ReferenceProperty field gets deleted it produces a ReferenceProperty related errors in all the other models where it has been used. What I want is, when a field is deleted say a User is deleted, all the fields having User as the ReferenceProperty should still work without any error messages displaying the associated user as unavailable or something like that.
Can someone please suggest how that can be done?
Thanks in advance.