"""
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 filtered_relation')
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
[文档]class Q(tree.Node):
"""
Encapsulate filters as objects that can then be combined logically (using
`&` and `|`).
"""
# Connection types
AND = 'AND'
OR = 'OR'
default = AND
conditional = True
def __init__(self, *args, **kwargs):
connector = kwargs.pop('_connector', None)
negated = kwargs.pop('_negated', False)
super().__init__(children=list(args) + sorted(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__)
if path.startswith('django.db.models.query_utils'):
path = path.replace('django.db.models.query_utils', 'django.db.models')
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)
if self.connector != self.default:
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):
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))
)
[文档]class FilteredRelation:
"""Specify custom filtering in the ON clause of SQL joins."""
def __init__(self, relation_name, *, condition=Q()):
if not relation_name:
raise ValueError('relation_name cannot be empty.')
self.relation_name = relation_name
self.alias = None
if not isinstance(condition, Q):
raise ValueError('condition argument must be a Q() instance.')
self.condition = condition
self.path = []
def __eq__(self, other):
return (
isinstance(other, self.__class__) and
self.relation_name == other.relation_name and
self.alias == other.alias and
self.condition == other.condition
)
def clone(self):
clone = FilteredRelation(self.relation_name, condition=self.condition)
clone.alias = self.alias
clone.path = self.path[:]
return clone
def resolve_expression(self, *args, **kwargs):
"""
QuerySet.annotate() only accepts expression-like arguments
(with a resolve_expression() method).
"""
raise NotImplementedError('FilteredRelation.resolve_expression() is unused.')
def as_sql(self, compiler, connection):
# Resolve the condition in Join.filtered_relation.
query = compiler.query
where = query.build_filtered_relation_q(self.condition, reuse=set(self.path))
return compiler.compile(where)
1月 11, 2019