session.evict(model) give "id column not null" if model table have a unique index and model has a unique error.

this table has a other primary index on id indentity column and for loginid unique index.

when try session.saveorupdate(model) and this model has already loginid in the table and given error, we try session.evict(model) after control session.contains(model) in this case session.evict(model) give upper error.
sessin.contains(model) return true for this model.

is anybody know solve this case.