app/django/db/models/query_utils.py
author Sverre Rabbelier <srabbelier@gmail.com>
Sat, 29 Aug 2009 14:30:52 -0700
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permissions -rw-r--r--
Use profiler.py to prevent import failures
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"""
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Various data structures used in query construction.
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Factored out from django.db.models.query so that they can also be used by other
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modules without getting into circular import difficulties.
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"""
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from copy import deepcopy
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from django.utils import tree
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class QueryWrapper(object):
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    """
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    A type that indicates the contents are an SQL fragment and the associate
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    parameters. Can be used to pass opaque data to a where-clause, for example.
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    """
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    def __init__(self, sql, params):
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        self.data = sql, params
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class Q(tree.Node):
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    """
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    Encapsulates filters as objects that can then be combined logically (using
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    & and |).
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    """
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    # Connection types
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    AND = 'AND'
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    OR = 'OR'
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    default = AND
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    def __init__(self, *args, **kwargs):
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        super(Q, self).__init__(children=list(args) + kwargs.items())
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    def _combine(self, other, conn):
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        if not isinstance(other, Q):
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            raise TypeError(other)
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        obj = deepcopy(self)
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        obj.add(other, conn)
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        return obj
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    def __or__(self, other):
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        return self._combine(other, self.OR)
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    def __and__(self, other):
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        return self._combine(other, self.AND)
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    def __invert__(self):
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        obj = deepcopy(self)
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        obj.negate()
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        return obj
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def select_related_descend(field, restricted, requested):
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    """
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    Returns True if this field should be used to descend deeper for
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    select_related() purposes. Used by both the query construction code
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    (sql.query.fill_related_selections()) and the model instance creation code
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    (query.get_cached_row()).
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    """
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    if not field.rel:
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        return False
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    if field.rel.parent_link:
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        return False
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    if restricted and field.name not in requested:
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        return False
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    if not restricted and field.null:
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        return False
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    return True
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