Removed query.alias_diff()

    return not hasattr(field, 'rel') and field.field.unique

def alias_diff(refcounts_before, refcounts_after):

    """

    Given the before and after copies of refcounts works out which aliases

    have been added to the after copy.

    """

    # Use -1 as default value so that any join that is created, then trimmed

    # is seen as added.

    return set(t for t in refcounts_after

               if refcounts_after[t] > refcounts_before.get(t, -1))

class JoinPromoter(object):

    """

    A class to abstract away join promotion problems for complex filter