'create a "get clause" based on the primary key.  this is used
by query.get() and many-to-one lazyloads to load this item
by primary key.'

@_memoized_configured_property
def _get_clause(self):

    params = [(primary_key, sql.bindparam(None, type_=primary_key.type)) for primary_key in self.primary_key]
    return (sql.and_(*[(k == v) for (k, v) in params]), util.column_dict(params))
