NHibernate parent-childs save redundant sql update executed

I'm trying to save (insert) parent object with a collection of child objects, all objects are new. I prefer to manually specify what t开发者_Python百科o save\update and when so I do not use any cascade saves in mappings and flush sessions by myself. So basically I save this object graph like:

session.Save(Parent)
foreach (var child in Parent.Childs)
{
 session.Save(child);
}
session.Flush()

I expect this code to insert Parent row, then each child row, however NHibernate executes this SQL:

INSERT INTO PARENT....
INSERT INTO CHILD ....
UPDATE CHILD SET ParentId=@1 WHERE Id=@2 //What the point of update if ParentId was set in previous query

This update statement is absolutely unnecessary, ParentId was already set correctly in INSERT. How do I get rid of it? Performance is very important for me.

I forgot "Inverse" in mappings on many-to-one collection.