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Source code for django.db.models.query_utils

"""
Various data structures used in query construction.

Factored out from django.db.models.query to avoid making the main module very
large and/or so that they can be used by other modules without getting into
circular import difficulties.
"""
from __future__ import unicode_literals

from collections import namedtuple

from django.core.exceptions import FieldDoesNotExist
from django.db.backends import utils
from django.db.models.constants import LOOKUP_SEP
from django.utils import six, tree

# PathInfo is used when converting lookups (fk__somecol). The contents
# describe the relation in Model terms (model Options and Fields for both
# sides of the relation. The join_field is the field backing the relation.
PathInfo = namedtuple('PathInfo', 'from_opts to_opts target_fields join_field m2m direct')


class InvalidQuery(Exception):
    """
    The query passed to raw isn't a safe query to use with raw.
    """
    pass


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, list(params)

    def as_sql(self, compiler=None, connection=None):
        return self.data


[docs]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) + list(six.iteritems(kwargs))) def _combine(self, other, conn): if not isinstance(other, Q): raise TypeError(other) obj = type(self)() obj.connector = conn obj.add(self, conn) 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 = type(self)() obj.add(self, self.AND) obj.negate() return obj def clone(self): clone = self.__class__._new_instance( children=[], connector=self.connector, negated=self.negated) for child in self.children: if hasattr(child, 'clone'): clone.children.append(child.clone()) else: clone.children.append(child) return clone def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False): # We must promote any new joins to left outer joins so that when Q is # used as an expression, rows aren't filtered due to joins. clause, joins = query._add_q(self, reuse, allow_joins=allow_joins, split_subq=False) query.promote_joins(joins) return clause @classmethod def _refs_aggregate(cls, obj, existing_aggregates): if not isinstance(obj, tree.Node): aggregate, aggregate_lookups = refs_aggregate(obj[0].split(LOOKUP_SEP), existing_aggregates) if not aggregate and hasattr(obj[1], 'refs_aggregate'): return obj[1].refs_aggregate(existing_aggregates) return aggregate, aggregate_lookups for c in obj.children: aggregate, aggregate_lookups = cls._refs_aggregate(c, existing_aggregates) if aggregate: return aggregate, aggregate_lookups return False, () def refs_aggregate(self, existing_aggregates): if not existing_aggregates: return False
return self._refs_aggregate(self, existing_aggregates) class DeferredAttribute(object): """ A wrapper for a deferred-loading field. When the value is read from this object the first time, the query is executed. """ def __init__(self, field_name, model): self.field_name = field_name def __get__(self, instance, owner): """ Retrieves and caches the value from the datastore on the first lookup. Returns the cached value. """ non_deferred_model = instance._meta.proxy_for_model opts = non_deferred_model._meta assert instance is not None data = instance.__dict__ if data.get(self.field_name, self) is self: # self.field_name is the attname of the field, but only() takes the # actual name, so we need to translate it here. try: f = opts.get_field(self.field_name) except FieldDoesNotExist: f = [f for f in opts.fields if f.attname == self.field_name][0] name = f.name # Let's see if the field is part of the parent chain. If so we # might be able to reuse the already loaded value. Refs #18343. val = self._check_parent_chain(instance, name) if val is None: instance.refresh_from_db(fields=[self.field_name]) val = getattr(instance, self.field_name) data[self.field_name] = val return data[self.field_name] def __set__(self, instance, value): """ Deferred loading attributes can be set normally (which means there will never be a database lookup involved. """ instance.__dict__[self.field_name] = value def _check_parent_chain(self, instance, name): """ Check if the field value can be fetched from a parent field already loaded in the instance. This can be done if the to-be fetched field is a primary key field. """ opts = instance._meta f = opts.get_field(name) link_field = opts.get_ancestor_link(f.model) if f.primary_key and f != link_field: return getattr(instance, link_field.attname) return None def select_related_descend(field, restricted, requested, load_fields, reverse=False): """ 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_klass_info()). Arguments: * field - the field to be checked * restricted - a boolean field, indicating if the field list has been manually restricted using a requested clause) * requested - The select_related() dictionary. * load_fields - the set of fields to be loaded on this model * reverse - boolean, True if we are checking a reverse select related """ if not field.rel: return False if field.rel.parent_link and not reverse: return False if restricted: if reverse and field.related_query_name() not in requested: return False if not reverse and field.name not in requested: return False if not restricted and field.null: return False if load_fields: if field.attname not in load_fields: if restricted and field.name in requested: raise InvalidQuery("Field %s.%s cannot be both deferred" " and traversed using select_related" " at the same time." % (field.model._meta.object_name, field.name)) return False return True # This function is needed because data descriptors must be defined on a class # object, not an instance, to have any effect. def deferred_class_factory(model, attrs): """ Returns a class object that is a copy of "model" with the specified "attrs" being replaced with DeferredAttribute objects. The "pk_value" ties the deferred attributes to a particular instance of the model. """ if not attrs: return model opts = model._meta # Never create deferred models based on deferred model if model._deferred: # Deferred models are proxies for the non-deferred model. We never # create chains of defers => proxy_for_model is the non-deferred # model. model = opts.proxy_for_model # The app registry wants a unique name for each model, otherwise the new # class won't be created (we get an exception). Therefore, we generate # the name using the passed in attrs. It's OK to reuse an existing class # object if the attrs are identical. name = "%s_Deferred_%s" % (model.__name__, '_'.join(sorted(list(attrs)))) name = utils.truncate_name(name, 80, 32) try: return opts.apps.get_model(model._meta.app_label, name) except LookupError: class Meta: proxy = True apps = opts.apps app_label = opts.app_label overrides = {attr: DeferredAttribute(attr, model) for attr in attrs} overrides["Meta"] = Meta overrides["__module__"] = model.__module__ overrides["_deferred"] = True return type(str(name), (model,), overrides) # The above function is also used to unpickle model instances with deferred # fields. deferred_class_factory.__safe_for_unpickling__ = True def refs_aggregate(lookup_parts, aggregates): """ A little helper method to check if the lookup_parts contains references to the given aggregates set. Because the LOOKUP_SEP is contained in the default annotation names we must check each prefix of the lookup_parts for a match. """ for n in range(len(lookup_parts) + 1): level_n_lookup = LOOKUP_SEP.join(lookup_parts[0:n]) if level_n_lookup in aggregates and aggregates[level_n_lookup].contains_aggregate: return aggregates[level_n_lookup], lookup_parts[n:] return False, () def refs_expression(lookup_parts, annotations): """ A helper method to check if the lookup_parts contains references to the given annotations set. Because the LOOKUP_SEP is contained in the default annotation names we must check each prefix of the lookup_parts for a match. """ for n in range(len(lookup_parts) + 1): level_n_lookup = LOOKUP_SEP.join(lookup_parts[0:n]) if level_n_lookup in annotations and annotations[level_n_lookup]: return annotations[level_n_lookup], lookup_parts[n:] return False, ()
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