• Language: en

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.
"""
import copy
import functools
import inspect
from collections import namedtuple

from django.db.models.constants import LOOKUP_SEP
from django.utils import 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


def subclasses(cls):
    yield cls
    for subclass in cls.__subclasses__():
        yield from subclasses(subclass)


class QueryWrapper:
    """
    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.
    """
    contains_aggregate = False

    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): """ Encapsulate filters as objects that can then be combined logically (using `&` and `|`). """ # Connection types AND = 'AND' OR = 'OR' default = AND def __init__(self, *args, **kwargs): connector = kwargs.pop('_connector', None) negated = kwargs.pop('_negated', False) super().__init__(children=list(args) + list(kwargs.items()), connector=connector, negated=negated) def _combine(self, other, conn): if not isinstance(other, Q): raise TypeError(other) # If the other Q() is empty, ignore it and just use `self`. if not other: return copy.deepcopy(self) # Or if this Q is empty, ignore it and just use `other`. elif not self: return copy.deepcopy(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 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 def deconstruct(self): path = '%s.%s' % (self.__class__.__module__, self.__class__.__name__) args, kwargs = (), {} if len(self.children) == 1 and not isinstance(self.children[0], Q): child = self.children[0] kwargs = {child[0]: child[1]} else: args = tuple(self.children) kwargs = {'_connector': self.connector} if self.negated: kwargs['_negated'] = True return path, args, kwargs
class DeferredAttribute: """ 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, cls=None): """ Retrieve and caches the value from the datastore on the first lookup. Return the cached value. """ if instance is None: return self data = instance.__dict__ if data.get(self.field_name, self) is self: # 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, self.field_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 _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 class RegisterLookupMixin: @classmethod def _get_lookup(cls, lookup_name): return cls.get_lookups().get(lookup_name, None) @classmethod @functools.lru_cache(maxsize=None) def get_lookups(cls): class_lookups = [parent.__dict__.get('class_lookups', {}) for parent in inspect.getmro(cls)] return cls.merge_dicts(class_lookups) def get_lookup(self, lookup_name): from django.db.models.lookups import Lookup found = self._get_lookup(lookup_name) if found is None and hasattr(self, 'output_field'): return self.output_field.get_lookup(lookup_name) if found is not None and not issubclass(found, Lookup): return None return found def get_transform(self, lookup_name): from django.db.models.lookups import Transform found = self._get_lookup(lookup_name) if found is None and hasattr(self, 'output_field'): return self.output_field.get_transform(lookup_name) if found is not None and not issubclass(found, Transform): return None return found @staticmethod def merge_dicts(dicts): """ Merge dicts in reverse to preference the order of the original list. e.g., merge_dicts([a, b]) will preference the keys in 'a' over those in 'b'. """ merged = {} for d in reversed(dicts): merged.update(d) return merged @classmethod def _clear_cached_lookups(cls): for subclass in subclasses(cls): subclass.get_lookups.cache_clear() @classmethod def register_lookup(cls, lookup, lookup_name=None): if lookup_name is None: lookup_name = lookup.lookup_name if 'class_lookups' not in cls.__dict__: cls.class_lookups = {} cls.class_lookups[lookup_name] = lookup cls._clear_cached_lookups() return lookup @classmethod def _unregister_lookup(cls, lookup, lookup_name=None): """ Remove given lookup from cls lookups. For use in tests only as it's not thread-safe. """ if lookup_name is None: lookup_name = lookup.lookup_name del cls.class_lookups[lookup_name] def select_related_descend(field, restricted, requested, load_fields, reverse=False): """ Return 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.remote_field: return False if field.remote_field.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 True def refs_expression(lookup_parts, annotations): """ Check if the lookup_parts contains references to the given annotations set. Because the LOOKUP_SEP is contained in the default annotation names, check each prefix of the lookup_parts for a match. """ for n in range(1, 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, () def check_rel_lookup_compatibility(model, target_opts, field): """ Check that self.model is compatible with target_opts. Compatibility is OK if: 1) model and opts match (where proxy inheritance is removed) 2) model is parent of opts' model or the other way around """ def check(opts): return ( model._meta.concrete_model == opts.concrete_model or opts.concrete_model in model._meta.get_parent_list() or model in opts.get_parent_list() ) # If the field is a primary key, then doing a query against the field's # model is ok, too. Consider the case: # class Restaurant(models.Model): # place = OnetoOneField(Place, primary_key=True): # Restaurant.objects.filter(pk__in=Restaurant.objects.all()). # If we didn't have the primary key check, then pk__in (== place__in) would # give Place's opts as the target opts, but Restaurant isn't compatible # with that. This logic applies only to primary keys, as when doing __in=qs, # we are going to turn this into __in=qs.values('pk') later on. return ( check(target_opts) or (getattr(field, 'primary_key', False) and check(field.model._meta)) )
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