app/django/db/models/query_utils.py
author Sverre Rabbelier <srabbelier@gmail.com>
Sat, 06 Dec 2008 14:23:53 +0000
changeset 679 77a286ff6667
parent 323 ff1a9aa48cfd
permissions -rw-r--r--
Introduce dynamic scope_path regexps Instead of relying on scope_path's being "one slash deep", we should instead allow for either: 1. scope_paths that have a pre-defined depth 2. scope_paths that can be arbitrarily deep We achieve 1 by setting an entities scope_logic to another logic module. We then recursively call getScopeDepth until we get to the topmost entity (that is, an unscoped entity). A little different is the solution to 2, since some entities can have an arbitrarily deep scope (such as Documents), we need to have some way of signaling this to getScopePattern. A clean solution is to return None, rather than a number. If None is returned, the SCOPE_PATH_ARG_PATTERN is returned as regexp instead, which will match an arbitrarily deeply nested scope. The solution for 2 requires that we return None somewhere in the scope_logic chain, the most straight forward method to do so is to override getScopeDepth anywhere such a scope is needed and make it return None. A more elegant solution however, is to set the scope_logic to that module in all entities that require it. Patch by: Sverre Rabbelier

"""
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