def fill_related_selections(self, opts=None, root_alias=None, cur_depth=1,
            requested=None, restricted=None, nullable=None):
        """
        Fill in the information needed for a select_related query. The current
        depth is measured as the number of connections away from the root model
        (for example, cur_depth=1 means we are looking at models with direct
        connections to the root model).
        """
        if not restricted and self.query.max_depth and cur_depth > self.query.max_depth:
            # We've recursed far enough; bail out.
            return

        if not opts:
            opts = self.query.get_meta()
            root_alias = self.query.get_initial_alias()
            self.query.related_select_cols = []
        only_load = self.query.get_loaded_field_names()

        # Setup for the case when only particular related fields should be
        # included in the related selection.
        if requested is None:
            if isinstance(self.query.select_related, dict):
                requested = self.query.select_related
                restricted = True
            else:
                restricted = False

        for f, model in opts.get_fields_with_model():
            # The get_fields_with_model() returns None for fields that live
            # in the field's local model. So, for those fields we want to use
            # the f.model - that is the field's local model.
            field_model = model or f.model
            if not select_related_descend(f, restricted, requested,
                                          only_load.get(field_model)):
                continue
            promote = nullable or f.null
            _, _, _, joins, _ = self.query.setup_joins(
                [f.name], opts, root_alias, outer_if_first=promote)
            alias = joins[-1]
            columns, _ = self.get_default_columns(start_alias=alias,
                    opts=f.rel.to._meta, as_pairs=True)
            self.query.related_select_cols.extend(
                SelectInfo((col[0], col[1].column), col[1]) for col in columns)
            if restricted:
                next = requested.get(f.name, {})
            else:
                next = False
            new_nullable = f.null or promote
            self.fill_related_selections(f.rel.to._meta, alias, cur_depth - 1,
                    next, restricted, new_nullable)

        if restricted:
            related_fields = [
                (o.field, o.model)
                for o in opts.get_all_related_objects()
                if o.field.unique
            ]
            for f, model in related_fields:
                if not select_related_descend(f, restricted, requested,
                                              only_load.get(model), reverse=True):
                    continue

                _, _, _, joins, _ = self.query.setup_joins(
                    [f.related_query_name()], opts, root_alias, outer_if_first=True)
                alias = joins[-1]
                from_parent = (opts.model if issubclass(model, opts.model)
                               else None)
                columns, _ = self.get_default_columns(start_alias=alias,
                    opts=model._meta, as_pairs=True, from_parent=from_parent)
                self.query.related_select_cols.extend(
                    SelectInfo((col[0], col[1].column), col[1]) for col in columns)
                next = requested.get(f.related_query_name(), {})
                # Use True here because we are looking at the _reverse_ side of
                # the relation, which is always nullable.
                new_nullable = True
                self.fill_related_selections(model._meta, alias, cur_depth + 1,
                                             next, restricted, new_nullable)
dataset/ETHPy150Open cloudera/hue/desktop/core/ext-py/Django-1.6.10/django/db/models/sql/compiler.py/SQLCompiler.fill_related_selections/operator `+` -> `-`