390 lines
13 KiB
Python
390 lines
13 KiB
Python
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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 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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import copy
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import functools
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import inspect
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import logging
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from collections import namedtuple
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from django.core.exceptions import FieldError
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from django.db import DEFAULT_DB_ALIAS, DatabaseError, connections
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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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logger = logging.getLogger("django.db.models")
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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(
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"PathInfo",
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"from_opts to_opts target_fields join_field m2m direct filtered_relation",
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)
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def subclasses(cls):
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yield cls
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for subclass in cls.__subclasses__():
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yield from subclasses(subclass)
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class Q(tree.Node):
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"""
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Encapsulate 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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XOR = "XOR"
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default = AND
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conditional = True
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def __init__(self, *args, _connector=None, _negated=False, **kwargs):
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super().__init__(
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children=[*args, *sorted(kwargs.items())],
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connector=_connector,
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negated=_negated,
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)
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def _combine(self, other, conn):
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if not (isinstance(other, Q) or getattr(other, "conditional", False) is True):
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raise TypeError(other)
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if not self:
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return other.copy() if hasattr(other, "copy") else copy.copy(other)
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elif isinstance(other, Q) and not other:
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_, args, kwargs = self.deconstruct()
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return type(self)(*args, **kwargs)
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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 __xor__(self, other):
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return self._combine(other, self.XOR)
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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 resolve_expression(
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self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False
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):
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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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clause, joins = query._add_q(
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self,
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reuse,
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allow_joins=allow_joins,
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split_subq=False,
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check_filterable=False,
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)
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query.promote_joins(joins)
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return clause
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def flatten(self):
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"""
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Recursively yield this Q object and all subexpressions, in depth-first
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order.
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"""
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yield self
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for child in self.children:
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if isinstance(child, tuple):
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# Use the lookup.
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child = child[1]
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if hasattr(child, "flatten"):
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yield from child.flatten()
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else:
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yield child
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def check(self, against, using=DEFAULT_DB_ALIAS):
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"""
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Do a database query to check if the expressions of the Q instance
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matches against the expressions.
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"""
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# Avoid circular imports.
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from django.db.models import BooleanField, Value
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from django.db.models.functions import Coalesce
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from django.db.models.sql import Query
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from django.db.models.sql.constants import SINGLE
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query = Query(None)
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for name, value in against.items():
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if not hasattr(value, "resolve_expression"):
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value = Value(value)
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query.add_annotation(value, name, select=False)
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query.add_annotation(Value(1), "_check")
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# This will raise a FieldError if a field is missing in "against".
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if connections[using].features.supports_comparing_boolean_expr:
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query.add_q(Q(Coalesce(self, True, output_field=BooleanField())))
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else:
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query.add_q(self)
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compiler = query.get_compiler(using=using)
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try:
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return compiler.execute_sql(SINGLE) is not None
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except DatabaseError as e:
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logger.warning("Got a database error calling check() on %r: %s", self, e)
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return True
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def deconstruct(self):
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path = "%s.%s" % (self.__class__.__module__, self.__class__.__name__)
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if path.startswith("django.db.models.query_utils"):
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path = path.replace("django.db.models.query_utils", "django.db.models")
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args = tuple(self.children)
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kwargs = {}
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if self.connector != self.default:
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kwargs["_connector"] = self.connector
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if self.negated:
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kwargs["_negated"] = True
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return path, args, kwargs
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class DeferredAttribute:
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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):
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self.field = field
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def __get__(self, instance, cls=None):
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"""
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Retrieve and caches the value from the datastore on the first lookup.
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Return the cached value.
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"""
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if instance is None:
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return self
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data = instance.__dict__
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field_name = self.field.attname
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if field_name not in data:
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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)
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if val is None:
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instance.refresh_from_db(fields=[field_name])
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else:
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data[field_name] = val
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return data[field_name]
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def _check_parent_chain(self, instance):
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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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link_field = opts.get_ancestor_link(self.field.model)
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if self.field.primary_key and self.field != link_field:
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return getattr(instance, link_field.attname)
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return None
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class RegisterLookupMixin:
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@classmethod
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def _get_lookup(cls, lookup_name):
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return cls.get_lookups().get(lookup_name, None)
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@classmethod
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@functools.lru_cache(maxsize=None)
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def get_lookups(cls):
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class_lookups = [
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parent.__dict__.get("class_lookups", {}) for parent in inspect.getmro(cls)
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]
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return cls.merge_dicts(class_lookups)
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def get_lookup(self, lookup_name):
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from django.db.models.lookups import Lookup
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found = self._get_lookup(lookup_name)
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if found is None and hasattr(self, "output_field"):
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return self.output_field.get_lookup(lookup_name)
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if found is not None and not issubclass(found, Lookup):
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return None
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return found
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def get_transform(self, lookup_name):
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from django.db.models.lookups import Transform
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found = self._get_lookup(lookup_name)
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if found is None and hasattr(self, "output_field"):
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return self.output_field.get_transform(lookup_name)
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if found is not None and not issubclass(found, Transform):
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return None
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return found
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@staticmethod
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def merge_dicts(dicts):
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"""
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Merge dicts in reverse to preference the order of the original list. e.g.,
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merge_dicts([a, b]) will preference the keys in 'a' over those in 'b'.
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"""
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merged = {}
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for d in reversed(dicts):
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merged.update(d)
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return merged
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@classmethod
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def _clear_cached_lookups(cls):
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for subclass in subclasses(cls):
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subclass.get_lookups.cache_clear()
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@classmethod
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def register_lookup(cls, lookup, lookup_name=None):
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if lookup_name is None:
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lookup_name = lookup.lookup_name
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if "class_lookups" not in cls.__dict__:
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cls.class_lookups = {}
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cls.class_lookups[lookup_name] = lookup
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cls._clear_cached_lookups()
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return lookup
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@classmethod
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def _unregister_lookup(cls, lookup, lookup_name=None):
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"""
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Remove given lookup from cls lookups. For use in tests only as it's
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not thread-safe.
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"""
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if lookup_name is None:
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lookup_name = lookup.lookup_name
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del cls.class_lookups[lookup_name]
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cls._clear_cached_lookups()
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def select_related_descend(field, restricted, requested, load_fields, reverse=False):
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"""
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Return 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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(compiler.get_related_selections()) and the model instance creation code
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(compiler.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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msg = (
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"Field %s.%s cannot be both deferred and traversed using "
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"select_related at the same time."
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) % (field.model._meta.object_name, field.name)
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raise FieldError(msg)
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return True
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def refs_expression(lookup_parts, annotations):
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"""
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Check if the lookup_parts contains references to the given annotations set.
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Because the LOOKUP_SEP is contained in the default annotation names, check
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each prefix of the lookup_parts for a match.
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"""
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for n in range(1, 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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def check_rel_lookup_compatibility(model, target_opts, field):
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"""
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Check that self.model is compatible with target_opts. Compatibility
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is OK if:
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1) model and opts match (where proxy inheritance is removed)
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2) model is parent of opts' model or the other way around
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"""
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def check(opts):
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return (
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model._meta.concrete_model == opts.concrete_model
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or opts.concrete_model in model._meta.get_parent_list()
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or model in opts.get_parent_list()
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)
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# If the field is a primary key, then doing a query against the field's
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# model is ok, too. Consider the case:
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# class Restaurant(models.Model):
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# place = OneToOneField(Place, primary_key=True):
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# Restaurant.objects.filter(pk__in=Restaurant.objects.all()).
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# If we didn't have the primary key check, then pk__in (== place__in) would
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# give Place's opts as the target opts, but Restaurant isn't compatible
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# with that. This logic applies only to primary keys, as when doing __in=qs,
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# we are going to turn this into __in=qs.values('pk') later on.
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return check(target_opts) or (
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getattr(field, "primary_key", False) and check(field.model._meta)
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)
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class FilteredRelation:
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"""Specify custom filtering in the ON clause of SQL joins."""
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def __init__(self, relation_name, *, condition=Q()):
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if not relation_name:
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raise ValueError("relation_name cannot be empty.")
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self.relation_name = relation_name
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self.alias = None
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if not isinstance(condition, Q):
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raise ValueError("condition argument must be a Q() instance.")
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self.condition = condition
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self.path = []
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def __eq__(self, other):
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if not isinstance(other, self.__class__):
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return NotImplemented
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return (
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self.relation_name == other.relation_name
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and self.alias == other.alias
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and self.condition == other.condition
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)
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def clone(self):
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clone = FilteredRelation(self.relation_name, condition=self.condition)
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clone.alias = self.alias
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clone.path = self.path[:]
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return clone
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def resolve_expression(self, *args, **kwargs):
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"""
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QuerySet.annotate() only accepts expression-like arguments
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(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)
|