+
−"""
+
−Various data structures used in query construction.
+
−
+
−Factored out from django.db.models.query so that they can also be used by other
+
−modules without getting into circular import difficulties.
+
−"""
+
−
+
−from copy import deepcopy
+
−
+
−from django.utils import tree
+
−
+
−class QueryWrapper(object):
+
−    """
+
−    A type that indicates the contents are an SQL fragment and the associate
+
−    parameters. Can be used to pass opaque data to a where-clause, for example.
+
−    """
+
−    def __init__(self, sql, params):
+
−        self.data = sql, params
+
−
+
−class Q(tree.Node):
+
−    """
+
−    Encapsulates filters as objects that can then be combined logically (using
+
−    & and |).
+
−    """
+
−    # Connection types
+
−    AND = 'AND'
+
−    OR = 'OR'
+
−    default = AND
+
−
+
−    def __init__(self, *args, **kwargs):
+
−        super(Q, self).__init__(children=list(args) + kwargs.items())
+
−
+
−    def _combine(self, other, conn):
+
−        if not isinstance(other, Q):
+
−            raise TypeError(other)
+
−        obj = deepcopy(self)
+
−        obj.add(other, conn)
+
−        return obj
+
−
+
−    def __or__(self, other):
+
−        return self._combine(other, self.OR)
+
−
+
−    def __and__(self, other):
+
−        return self._combine(other, self.AND)
+
−
+
−    def __invert__(self):
+
−        obj = deepcopy(self)
+
−        obj.negate()
+
−        return obj
+
−
+
−def select_related_descend(field, restricted, requested):
+
−    """
+
−    Returns True if this field should be used to descend deeper for
+
−    select_related() purposes. Used by both the query construction code
+
−    (sql.query.fill_related_selections()) and the model instance creation code
+
−    (query.get_cached_row()).
+
−    """
+
−    if not field.rel:
+
−        return False
+
−    if field.rel.parent_link:
+
−        return False
+
−    if restricted and field.name not in requested:
+
−        return False
+
−    if not restricted and field.null:
+
−        return False
+
−    return True
+
−