subqueries.py 文件源码

def delete_qs(self, query, using):
        """
        Delete the queryset in one SQL query (if possible). For simple queries
        this is done by copying the query.query.where to self.query, for
        complex queries by using subquery.
        """
        innerq = query.query
        # Make sure the inner query has at least one table in use.
        innerq.get_initial_alias()
        # The same for our new query.
        self.get_initial_alias()
        innerq_used_tables = [t for t in innerq.tables
                              if innerq.alias_refcount[t]]
        if not innerq_used_tables or innerq_used_tables == self.tables:
            # There is only the base table in use in the query.
            self.where = innerq.where
        else:
            pk = query.model._meta.pk
            if not connections[using].features.update_can_self_select:
                # We can't do the delete using subquery.
                values = list(query.values_list('pk', flat=True))
                if not values:
                    return 0
                return self.delete_batch(values, using)
            else:
                innerq.clear_select_clause()
                innerq.select = [
                    pk.get_col(self.get_initial_alias())
                ]
                values = innerq
            self.where = self.where_class()
            self.add_q(Q(pk__in=values))
        cursor = self.get_compiler(using).execute_sql(CURSOR)
        return cursor.rowcount if cursor else 0