282 lines
10 KiB
Python
282 lines
10 KiB
Python
"""
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Various data structures used in query construction.
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Factored out from django.db.models.query to avoid making the main module very
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large and/or so that they can be used by other modules without getting into
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circular import difficulties.
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"""
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from __future__ import unicode_literals
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from collections import namedtuple
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from django.apps import apps
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from django.core.exceptions import FieldDoesNotExist
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from django.db.backends import utils
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from django.db.models.constants import LOOKUP_SEP
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from django.utils import tree
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# PathInfo is used when converting lookups (fk__somecol). The contents
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# describe the relation in Model terms (model Options and Fields for both
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# sides of the relation. The join_field is the field backing the relation.
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PathInfo = namedtuple('PathInfo', 'from_opts to_opts target_fields join_field m2m direct')
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class InvalidQuery(Exception):
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"""
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The query passed to raw isn't a safe query to use with raw.
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"""
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pass
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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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contains_aggregate = False
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def __init__(self, sql, params):
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self.data = sql, list(params)
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def as_sql(self, compiler=None, connection=None):
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return self.data
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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) + list(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 = type(self)()
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obj.connector = conn
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obj.add(self, conn)
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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 = type(self)()
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obj.add(self, self.AND)
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obj.negate()
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return obj
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def clone(self):
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clone = self.__class__._new_instance(
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children=[], connector=self.connector, negated=self.negated)
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for child in self.children:
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if hasattr(child, 'clone'):
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clone.children.append(child.clone())
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else:
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clone.children.append(child)
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return clone
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def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
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# We must promote any new joins to left outer joins so that when Q is
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# used as an expression, rows aren't filtered due to joins.
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joins_before = query.tables[:]
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clause, joins = query._add_q(self, reuse, allow_joins=allow_joins)
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joins_to_promote = [j for j in joins if j not in joins_before]
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query.promote_joins(joins_to_promote)
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return clause
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@classmethod
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def _refs_aggregate(cls, obj, existing_aggregates):
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if not isinstance(obj, tree.Node):
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aggregate, aggregate_lookups = refs_aggregate(obj[0].split(LOOKUP_SEP), existing_aggregates)
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if not aggregate and hasattr(obj[1], 'refs_aggregate'):
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return obj[1].refs_aggregate(existing_aggregates)
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return aggregate, aggregate_lookups
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for c in obj.children:
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aggregate, aggregate_lookups = cls._refs_aggregate(c, existing_aggregates)
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if aggregate:
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return aggregate, aggregate_lookups
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return False, ()
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def refs_aggregate(self, existing_aggregates):
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if not existing_aggregates:
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return False
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return self._refs_aggregate(self, existing_aggregates)
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class DeferredAttribute(object):
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"""
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A wrapper for a deferred-loading field. When the value is read from this
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object the first time, the query is executed.
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"""
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def __init__(self, field_name, model):
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self.field_name = field_name
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def __get__(self, instance, owner):
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"""
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Retrieves and caches the value from the datastore on the first lookup.
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Returns the cached value.
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"""
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non_deferred_model = instance._meta.proxy_for_model
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opts = non_deferred_model._meta
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assert instance is not None
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data = instance.__dict__
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if data.get(self.field_name, self) is self:
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# self.field_name is the attname of the field, but only() takes the
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# actual name, so we need to translate it here.
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try:
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f = opts.get_field(self.field_name)
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except FieldDoesNotExist:
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f = [f for f in opts.fields if f.attname == self.field_name][0]
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name = f.name
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# Let's see if the field is part of the parent chain. If so we
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# might be able to reuse the already loaded value. Refs #18343.
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val = self._check_parent_chain(instance, name)
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if val is None:
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instance.refresh_from_db(fields=[self.field_name])
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val = getattr(instance, self.field_name)
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data[self.field_name] = val
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return data[self.field_name]
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def __set__(self, instance, value):
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"""
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Deferred loading attributes can be set normally (which means there will
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never be a database lookup involved.
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"""
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instance.__dict__[self.field_name] = value
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def _check_parent_chain(self, instance, name):
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"""
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Check if the field value can be fetched from a parent field already
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loaded in the instance. This can be done if the to-be fetched
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field is a primary key field.
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"""
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opts = instance._meta
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f = opts.get_field(name)
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link_field = opts.get_ancestor_link(f.model)
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if f.primary_key and f != link_field:
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return getattr(instance, link_field.attname)
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return None
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def select_related_descend(field, restricted, requested, load_fields, reverse=False):
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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_klass_info()).
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Arguments:
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* field - the field to be checked
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* restricted - a boolean field, indicating if the field list has been
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manually restricted using a requested clause)
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* requested - The select_related() dictionary.
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* load_fields - the set of fields to be loaded on this model
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* reverse - boolean, True if we are checking a reverse select related
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"""
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if not field.remote_field:
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return False
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if field.remote_field.parent_link and not reverse:
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return False
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if restricted:
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if reverse and field.related_query_name() not in requested:
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return False
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if not reverse 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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if load_fields:
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if field.attname not in load_fields:
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if restricted and field.name in requested:
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raise InvalidQuery("Field %s.%s cannot be both deferred"
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" and traversed using select_related"
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" at the same time." %
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(field.model._meta.object_name, field.name))
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return False
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return True
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# This function is needed because data descriptors must be defined on a class
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# object, not an instance, to have any effect.
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def deferred_class_factory(model, attrs):
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"""
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Returns a class object that is a copy of "model" with the specified "attrs"
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being replaced with DeferredAttribute objects. The "pk_value" ties the
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deferred attributes to a particular instance of the model.
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"""
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if not attrs:
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return model
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# Never create deferred models based on deferred model
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if model._deferred:
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# Deferred models are proxies for the non-deferred model. We never
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# create chains of defers => proxy_for_model is the non-deferred
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# model.
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model = model._meta.proxy_for_model
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# The app registry wants a unique name for each model, otherwise the new
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# class won't be created (we get an exception). Therefore, we generate
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# the name using the passed in attrs. It's OK to reuse an existing class
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# object if the attrs are identical.
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name = "%s_Deferred_%s" % (model.__name__, '_'.join(sorted(list(attrs))))
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name = utils.truncate_name(name, 80, 32)
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try:
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return apps.get_model(model._meta.app_label, name)
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except LookupError:
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class Meta:
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proxy = True
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app_label = model._meta.app_label
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overrides = {attr: DeferredAttribute(attr, model) for attr in attrs}
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overrides["Meta"] = Meta
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overrides["__module__"] = model.__module__
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overrides["_deferred"] = True
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return type(str(name), (model,), overrides)
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# The above function is also used to unpickle model instances with deferred
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# fields.
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deferred_class_factory.__safe_for_unpickling__ = True
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def refs_aggregate(lookup_parts, aggregates):
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"""
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A helper method to check if the lookup_parts contains references
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to the given aggregates set. Because the LOOKUP_SEP is contained in the
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default annotation names we must check each prefix of the lookup_parts
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for a match.
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"""
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for n in range(len(lookup_parts) + 1):
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level_n_lookup = LOOKUP_SEP.join(lookup_parts[0:n])
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if level_n_lookup in aggregates and aggregates[level_n_lookup].contains_aggregate:
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return aggregates[level_n_lookup], lookup_parts[n:]
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return False, ()
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def refs_expression(lookup_parts, annotations):
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"""
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A helper method to check if the lookup_parts contains references
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to the given annotations set. Because the LOOKUP_SEP is contained in the
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default annotation names we must check each prefix of the lookup_parts
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for a match.
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"""
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for n in range(len(lookup_parts) + 1):
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level_n_lookup = LOOKUP_SEP.join(lookup_parts[0:n])
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if level_n_lookup in annotations and annotations[level_n_lookup]:
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return annotations[level_n_lookup], lookup_parts[n:]
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return False, ()
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