While writing Unit Tests for my membership provider code, I tried adding a permission
I had defined on one test user to a different test user. I was completely freaked
out, since user1 suddenly no longer had that permission.

What kind of witchery is this? Does Collection<T>.Add() remove items from the
source collection?

No. It doesn’t. I tried it all with simple collections. List<string>.Add() doesn’t
have this effect. So what’s going on?

The problem has to be in my persistence layer. My User and Permissions objects are
provided by LLBLGen. So it’s gotta be something in there. (A light dawns). I look
back at my table definitions. Sure enough, a permission as a m:1 relationship with
it’s user. A permission entity can’t belong to more than one user. And LLBLGen is
smart enough that when I take the object in the graph and add it to a different user,
it not only updates the relationship(FK), but removes it from the original object.

But how do I get the result I wanted? A simple duplication of an existing permission?
I adapted the deep
copy method I found over on Stack Overflow into a general extension method and
used it to dupe the permission as I added it. Clean copy in the object graph=>no
changes to the relationship(FK)=>success.

 public static class DeepCloneExtension
{ public static T
DeepClone<T>(this T
obj) { using (var
ms = new MemoryStream())
{ var formatter = new BinaryFormatter();
formatter.Serialize(ms, obj); ms.Position = 0; return (T)formatter.Deserialize(ms);
} } }