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You are reading an old version of the Evennia documentation. The latest version is here

.

# 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 functools
    import inspect
    import logging
    from collections import namedtuple

    from django.core.exceptions import FieldError
    from django.db import DEFAULT_DB_ALIAS, DatabaseError, connections
    from django.db.models.constants import LOOKUP_SEP
    from django.utils import tree

    logger = logging.getLogger("django.db.models")

    # 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",
    )

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

    class Q(tree.Node):
        """
        Encapsulate filters as objects that can then be combined logically (using
        `&` and `|`).
        """

        # Connection types
        AND = "AND"
        OR = "OR"
        XOR = "XOR"
        default = AND
        conditional = True

        def __init__(self, *args, _connector=None, _negated=False, **kwargs):
            super().__init__(
                children=[*args, *sorted(kwargs.items())],
                connector=_connector,
                negated=_negated,
            )

        def _combine(self, other, conn):
            if getattr(other, "conditional", False) is False:
                raise TypeError(other)
            if not self:
                return other.copy()
            if not other and isinstance(other, Q):
                return self.copy()

            obj = self.create(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 __xor__(self, other):
            return self._combine(other, self.XOR)

        def __invert__(self):
            obj = self.copy()
            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,
                check_filterable=False,
                summarize=summarize,
            )
            query.promote_joins(joins)
            return clause

        def flatten(self):
            """
            Recursively yield this Q object and all subexpressions, in depth-first
            order.
            """
            yield self
            for child in self.children:
                if isinstance(child, tuple):
                    # Use the lookup.
                    child = child[1]
                if hasattr(child, "flatten"):
                    yield from child.flatten()
                else:
                    yield child

        def check(self, against, using=DEFAULT_DB_ALIAS):
            """
            Do a database query to check if the expressions of the Q instance
            matches against the expressions.
            """
            # Avoid circular imports.
            from django.db.models import BooleanField, Value
            from django.db.models.functions import Coalesce
            from django.db.models.sql import Query
            from django.db.models.sql.constants import SINGLE

            query = Query(None)
            for name, value in against.items():
                if not hasattr(value, "resolve_expression"):
                    value = Value(value)
                query.add_annotation(value, name, select=False)
            query.add_annotation(Value(1), "_check")
            # This will raise a FieldError if a field is missing in "against".
            if connections[using].features.supports_comparing_boolean_expr:
                query.add_q(Q(Coalesce(self, True, output_field=BooleanField())))
            else:
                query.add_q(self)
            compiler = query.get_compiler(using=using)
            try:
                return compiler.execute_sql(SINGLE) is not None
            except DatabaseError as e:
                logger.warning("Got a database error calling check() on %r: %s", self, e)
                return True

        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 = tuple(self.children)
            kwargs = {}
            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):
            self.field = field

        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__
            field_name = self.field.attname
            if field_name not in data:
                # 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)
                if val is None:
                    instance.refresh_from_db(fields=[field_name])
                else:
                    data[field_name] = val
            return data[field_name]

        def _check_parent_chain(self, instance):
            """
            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
            link_field = opts.get_ancestor_link(self.field.model)
            if self.field.primary_key and self.field != link_field:
                return getattr(instance, link_field.attname)
            return None

    class class_or_instance_method:
        """
        Hook used in RegisterLookupMixin to return partial functions depending on
        the caller type (instance or class of models.Field).
        """

        def __init__(self, class_method, instance_method):
            self.class_method = class_method
            self.instance_method = instance_method

        def __get__(self, instance, owner):
            if instance is None:
                return functools.partial(self.class_method, owner)
            return functools.partial(self.instance_method, instance)

    class RegisterLookupMixin:
        def _get_lookup(self, lookup_name):
            return self.get_lookups().get(lookup_name, None)

        @functools.lru_cache(maxsize=None)
        def get_class_lookups(cls):
            class_lookups = [
                parent.__dict__.get("class_lookups", {}) for parent in inspect.getmro(cls)
            ]
            return cls.merge_dicts(class_lookups)

        def get_instance_lookups(self):
            class_lookups = self.get_class_lookups()
            if instance_lookups := getattr(self, "instance_lookups", None):
                return {**class_lookups, **instance_lookups}
            return class_lookups

        get_lookups = class_or_instance_method(get_class_lookups, get_instance_lookups)
        get_class_lookups = classmethod(get_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_class_lookups(cls):
            for subclass in subclasses(cls):
                subclass.get_class_lookups.cache_clear()

        def register_class_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_class_lookups()
            return lookup

        def register_instance_lookup(self, lookup, lookup_name=None):
            if lookup_name is None:
                lookup_name = lookup.lookup_name
            if "instance_lookups" not in self.__dict__:
                self.instance_lookups = {}
            self.instance_lookups[lookup_name] = lookup
            return lookup

        register_lookup = class_or_instance_method(
            register_class_lookup, register_instance_lookup
        )
        register_class_lookup = classmethod(register_class_lookup)

        def _unregister_class_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]
            cls._clear_cached_class_lookups()

        def _unregister_instance_lookup(self, lookup, lookup_name=None):
            """
            Remove given lookup from instance lookups. For use in tests only as
            it's not thread-safe.
            """
            if lookup_name is None:
                lookup_name = lookup.lookup_name
            del self.instance_lookups[lookup_name]

        _unregister_lookup = class_or_instance_method(
            _unregister_class_lookup, _unregister_instance_lookup
        )
        _unregister_class_lookup = classmethod(_unregister_class_lookup)

    def select_related_descend(field, restricted, requested, select_mask, reverse=False):
        """
        Return True if this field should be used to descend deeper for
        select_related() purposes. Used by both the query construction code
        (compiler.get_related_selections()) and the model instance creation code
        (compiler.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.
         * select_mask - the dictionary of selected fields.
         * 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 (
            restricted
            and select_mask
            and field.name in requested
            and field not in select_mask
        ):
            raise FieldError(
                f"Field {field.model._meta.object_name}.{field.name} cannot be both "
                "deferred and traversed using select_related at the same time."
            )
        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 annotations.get(level_n_lookup):
                return level_n_lookup, lookup_parts[n:]
        return None, ()

    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)
        )

    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):
            if not isinstance(other, self.__class__):
                return NotImplemented
            return (
                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)

Note

You are reading an old version of the Evennia documentation. The latest version is here

.