273 lines
9.5 KiB
Python
273 lines
9.5 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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import functools
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import inspect
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from collections import namedtuple
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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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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 QueryWrapper:
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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().__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 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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clause, joins = query._add_q(self, reuse, allow_joins=allow_joins, split_subq=False)
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query.promote_joins(joins)
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return clause
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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_name, model):
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self.field_name = field_name
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def __get__(self, instance, cls=None):
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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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if instance is None:
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return self
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data = instance.__dict__
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if data.get(self.field_name, self) is self:
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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, self.field_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 _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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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 = [parent.__dict__.get('class_lookups', {}) for parent in inspect.getmro(cls)]
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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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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 True
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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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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 or
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opts.concrete_model in model._meta.get_parent_list() or
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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 (
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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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