Fixed #20939 -- Simplified query generation by converting QuerySet to Query.

Thanks Anssi Kääriäinen for the initial patch and Anssi, Simon Charette,
and Josh Smeaton for review.

django/contrib/gis/db/models/lookups.py

@@ -6,6 +6,7 @@ from django.core.exceptions import FieldDoesNotExist
 from django.db.models.constants import LOOKUP_SEP
 from django.db.models.expressions import Col, Expression
 from django.db.models.lookups import BuiltinLookup, Lookup, Transform
+from django.db.models.sql.query import Query
 from django.utils import six
 
 gis_lookups = {}
@@ -100,8 +101,8 @@ class GISLookup(Lookup):
         return ('%s', params)
 
     def process_rhs(self, compiler, connection):
-        if hasattr(self.rhs, '_as_sql'):
-            # If rhs is some QuerySet, don't touch it
+        if isinstance(self.rhs, Query):
+            # If rhs is some Query, don't touch it.
             return super(GISLookup, self).process_rhs(compiler, connection)
 
         geom = self.rhs

django/db/backends/oracle/compiler.py

@@ -2,7 +2,7 @@ from django.db.models.sql import compiler
 
 
 class SQLCompiler(compiler.SQLCompiler):
-    def as_sql(self, with_limits=True, with_col_aliases=False, subquery=False):
+    def as_sql(self, with_limits=True, with_col_aliases=False):
         """
         Creates the SQL for this query. Returns the SQL string and list
         of parameters.  This is overridden from the original Query class
@@ -19,13 +19,11 @@ class SQLCompiler(compiler.SQLCompiler):
             sql, params = super(SQLCompiler, self).as_sql(
                 with_limits=False,
                 with_col_aliases=with_col_aliases,
-                subquery=subquery,
             )
         else:
             sql, params = super(SQLCompiler, self).as_sql(
                 with_limits=False,
                 with_col_aliases=True,
-                subquery=subquery,
             )
             # Wrap the base query in an outer SELECT * with boundaries on
             # the "_RN" column.  This is the canonical way to emulate LIMIT

django/db/models/fields/related_lookups.py

@@ -81,27 +81,18 @@ class RelatedIn(In):
                     AND)
             return root_constraint.as_sql(compiler, connection)
         else:
+            if getattr(self.rhs, '_forced_pk', False):
+                self.rhs.clear_select_clause()
+                if getattr(self.lhs.output_field, 'primary_key', False):
+                    # A case like Restaurant.objects.filter(place__in=restaurant_qs),
+                    # where place is a OneToOneField and the primary key of
+                    # Restaurant.
+                    target_field = self.lhs.field.name
+                else:
+                    target_field = self.lhs.field.target_field.name
+                self.rhs.add_fields([target_field], True)
             return super(RelatedIn, self).as_sql(compiler, connection)
 
-    def __getstate__(self):
-        """
-        Prevent pickling a query with an __in=inner_qs lookup from evaluating
-        inner_qs.
-        """
-        from django.db.models.query import QuerySet  # Avoid circular import
-        state = self.__dict__.copy()
-        if isinstance(self.rhs, QuerySet):
-            state['rhs'] = (self.rhs.__class__, self.rhs.query)
-        return state
-
-    def __setstate__(self, state):
-        self.__dict__.update(state)
-        if isinstance(self.rhs, tuple):
-            queryset_class, query = self.rhs
-            queryset = queryset_class()
-            queryset.query = query
-            self.rhs = queryset
-
 
 class RelatedLookupMixin(object):
     def get_prep_lookup(self):

django/db/models/lookups.py

@@ -26,9 +26,8 @@ class Lookup(object):
         if bilateral_transforms:
             # Warn the user as soon as possible if they are trying to apply
             # a bilateral transformation on a nested QuerySet: that won't work.
-            # We need to import QuerySet here so as to avoid circular
-            from django.db.models.query import QuerySet
-            if isinstance(rhs, QuerySet):
+            from django.db.models.sql.query import Query  # avoid circular import
+            if isinstance(rhs, Query):
                 raise NotImplementedError("Bilateral transformations on nested querysets are not supported.")
         self.bilateral_transforms = bilateral_transforms
 
@@ -79,24 +78,19 @@ class Lookup(object):
             value = value.resolve_expression(compiler.query)
         # Due to historical reasons there are a couple of different
         # ways to produce sql here. get_compiler is likely a Query
-        # instance, _as_sql QuerySet and as_sql just something with
-        # as_sql. Finally the value can of course be just plain
-        # Python value.
+        # instance and as_sql just something with as_sql. Finally the value
+        # can of course be just plain Python value.
         if hasattr(value, 'get_compiler'):
             value = value.get_compiler(connection=connection)
         if hasattr(value, 'as_sql'):
             sql, params = compiler.compile(value)
             return '(' + sql + ')', params
-        if hasattr(value, '_as_sql'):
-            sql, params = value._as_sql(connection=connection)
-            return '(' + sql + ')', params
         else:
             return self.get_db_prep_lookup(value, connection)
 
     def rhs_is_direct_value(self):
         return not(
             hasattr(self.rhs, 'as_sql') or
-            hasattr(self.rhs, '_as_sql') or
             hasattr(self.rhs, 'get_compiler'))
 
     def relabeled_clone(self, relabels):
@@ -371,8 +365,7 @@ class PatternLookup(BuiltinLookup):
         # So, for Python values we don't need any special pattern, but for
         # SQL reference values or SQL transformations we need the correct
         # pattern added.
-        if (hasattr(self.rhs, 'get_compiler') or hasattr(self.rhs, 'as_sql') or
-                hasattr(self.rhs, '_as_sql') or self.bilateral_transforms):
+        if hasattr(self.rhs, 'get_compiler') or hasattr(self.rhs, 'as_sql') or self.bilateral_transforms:
             pattern = connection.pattern_ops[self.lookup_name].format(connection.pattern_esc)
             return pattern.format(rhs)
         else:

django/db/models/query.py

@@ -19,9 +19,7 @@ from django.db.models.deletion import Collector
 from django.db.models.expressions import F
 from django.db.models.fields import AutoField
 from django.db.models.functions import Trunc
-from django.db.models.query_utils import (
-    InvalidQuery, Q, check_rel_lookup_compatibility,
-)
+from django.db.models.query_utils import InvalidQuery, Q
 from django.db.models.sql.constants import CURSOR
 from django.utils import six, timezone
 from django.utils.deprecation import RemovedInDjango20Warning
@@ -1114,36 +1112,17 @@ class QuerySet(object):
         for field, objects in other._known_related_objects.items():
             self._known_related_objects.setdefault(field, {}).update(objects)
 
-    def _prepare(self, field):
-        if self._fields is not None:
-            # values() queryset can only be used as nested queries
-            # if they are set up to select only a single field.
-            if len(self._fields or self.model._meta.concrete_fields) > 1:
-                raise TypeError('Cannot use multi-field values as a filter value.')
-        elif self.model != field.model:
-            # If the query is used as a subquery for a ForeignKey with non-pk
-            # target field, make sure to select the target field in the subquery.
-            foreign_fields = getattr(field, 'foreign_related_fields', ())
-            if len(foreign_fields) == 1 and not foreign_fields[0].primary_key:
-                return self.values(foreign_fields[0].name)
-        return self
-
-    def _as_sql(self, connection):
-        """
-        Returns the internal query's SQL and parameters (as a tuple).
-        """
-        if self._fields is not None:
+    def _prepare_as_filter_value(self):
+        if self._fields is None:
+            queryset = self.values('pk')
+            queryset.query._forced_pk = True
+        else:
             # values() queryset can only be used as nested queries
             # if they are set up to select only a single field.
-            if len(self._fields or self.model._meta.concrete_fields) > 1:
+            if len(self._fields) > 1:
                 raise TypeError('Cannot use multi-field values as a filter value.')
-            clone = self._clone()
-        else:
-            clone = self.values('pk')
-
-        if clone._db is None or connection == connections[clone._db]:
-            return clone.query.get_compiler(connection=connection).as_nested_sql()
-        raise ValueError("Can't do subqueries with queries on different DBs.")
+            queryset = self._clone()
+        return queryset.query.as_subquery_filter(queryset._db)
 
     def _add_hints(self, **hints):
         """
@@ -1161,21 +1140,6 @@ class QuerySet(object):
         """
         return self.query.has_filters()
 
-    def is_compatible_query_object_type(self, opts, field):
-        """
-        Check that using this queryset as the rhs value for a lookup is
-        allowed. The opts are the options of the relation's target we are
-        querying against. For example in .filter(author__in=Author.objects.all())
-        the opts would be Author's (from the author field) and self.model would
-        be Author.objects.all() queryset's .model (Author also). The field is
-        the related field on the lhs side.
-        """
-        # We trust that users of values() know what they are doing.
-        if self._fields is not None:
-            return True
-        return check_rel_lookup_compatibility(self.model, opts, field)
-    is_compatible_query_object_type.queryset_only = True
-
 
 class InstanceCheckMeta(type):
     def __instancecheck__(self, instance):

django/db/models/sql/compiler.py

@@ -13,6 +13,8 @@ from django.db.transaction import TransactionManagementError
 from django.db.utils import DatabaseError
 from django.utils.six.moves import zip
 
+FORCE = object()
+
 
 class SQLCompiler(object):
     def __init__(self, query, connection, using):
@@ -28,7 +30,6 @@ class SQLCompiler(object):
         self.annotation_col_map = None
         self.klass_info = None
         self.ordering_parts = re.compile(r'(.*)\s(ASC|DESC)(.*)')
-        self.subquery = False
 
     def setup_query(self):
         if all(self.query.alias_refcount[a] == 0 for a in self.query.tables):
@@ -355,11 +356,11 @@ class SQLCompiler(object):
             sql, params = vendor_impl(self, self.connection)
         else:
             sql, params = node.as_sql(self, self.connection)
-        if select_format and not self.subquery:
+        if select_format is FORCE or (select_format and not self.query.subquery):
             return node.output_field.select_format(self, sql, params)
         return sql, params
 
-    def as_sql(self, with_limits=True, with_col_aliases=False, subquery=False):
+    def as_sql(self, with_limits=True, with_col_aliases=False):
         """
         Creates the SQL for this query. Returns the SQL string and list of
         parameters.
@@ -367,7 +368,6 @@ class SQLCompiler(object):
         If 'with_limits' is False, any limit/offset information is not included
         in the query.
         """
-        self.subquery = subquery
         refcounts_before = self.query.alias_refcount.copy()
         try:
             extra_select, order_by, group_by = self.pre_sql_setup()
@@ -466,24 +466,6 @@ class SQLCompiler(object):
             # Finally do cleanup - get rid of the joins we created above.
             self.query.reset_refcounts(refcounts_before)
 
-    def as_nested_sql(self):
-        """
-        Perform the same functionality as the as_sql() method, returning an
-        SQL string and parameters. However, the alias prefixes are bumped
-        beforehand (in a copy -- the current query isn't changed), and any
-        ordering is removed if the query is unsliced.
-
-        Used when nesting this query inside another.
-        """
-        obj = self.query.clone()
-        # It's safe to drop ordering if the queryset isn't using slicing,
-        # distinct(*fields) or select_for_update().
-        if (obj.low_mark == 0 and obj.high_mark is None and
-                not self.query.distinct_fields and
-                not self.query.select_for_update):
-            obj.clear_ordering(True)
-        return obj.get_compiler(connection=self.connection).as_sql(subquery=True)
-
     def get_default_columns(self, start_alias=None, opts=None, from_parent=None):
         """
         Computes the default columns for selecting every field in the base
@@ -1218,7 +1200,7 @@ class SQLAggregateCompiler(SQLCompiler):
         """
         sql, params = [], []
         for annotation in self.query.annotation_select.values():
-            ann_sql, ann_params = self.compile(annotation, select_format=True)
+            ann_sql, ann_params = self.compile(annotation, select_format=FORCE)
             sql.append(ann_sql)
             params.extend(ann_params)
         self.col_count = len(self.query.annotation_select)

django/db/models/sql/query.py

@@ -143,6 +143,7 @@ class Query(object):
         self.standard_ordering = True
         self.used_aliases = set()
         self.filter_is_sticky = False
+        self.subquery = False
 
         # SQL-related attributes
         # Select and related select clauses are expressions to use in the
@@ -319,6 +320,7 @@ class Query(object):
         else:
             obj.used_aliases = set()
         obj.filter_is_sticky = False
+        obj.subquery = self.subquery
         if 'alias_prefix' in self.__dict__:
             obj.alias_prefix = self.alias_prefix
         if 'subq_aliases' in self.__dict__:
@@ -964,6 +966,9 @@ class Query(object):
         self.append_annotation_mask([alias])
         self.annotations[alias] = annotation
 
+    def _prepare_as_filter_value(self):
+        return self.clone()
+
     def prepare_lookup_value(self, value, lookups, can_reuse, allow_joins=True):
         # Default lookup if none given is exact.
         used_joins = []
@@ -974,8 +979,7 @@ class Query(object):
         if value is None:
             if lookups[-1] not in ('exact', 'iexact'):
                 raise ValueError("Cannot use None as a query value")
-            lookups[-1] = 'isnull'
-            value = True
+            return True, ['isnull'], used_joins
         elif hasattr(value, 'resolve_expression'):
             pre_joins = self.alias_refcount.copy()
             value = value.resolve_expression(self, reuse=can_reuse, allow_joins=allow_joins)
@@ -997,11 +1001,8 @@ class Query(object):
         # Subqueries need to use a different set of aliases than the
         # outer query. Call bump_prefix to change aliases of the inner
         # query (the value).
-        if hasattr(value, 'query') and hasattr(value.query, 'bump_prefix'):
-            value = value._clone()
-            value.query.bump_prefix(self)
-        if hasattr(value, 'bump_prefix'):
-            value = value.clone()
+        if hasattr(value, '_prepare_as_filter_value'):
+            value = value._prepare_as_filter_value()
             value.bump_prefix(self)
         # For Oracle '' is equivalent to null. The check needs to be done
         # at this stage because join promotion can't be done at compiler
@@ -1049,14 +1050,20 @@ class Query(object):
         Checks the type of object passed to query relations.
         """
         if field.is_relation:
-            # QuerySets implement is_compatible_query_object_type() to
-            # determine compatibility with the given field.
-            if hasattr(value, 'is_compatible_query_object_type'):
-                if not value.is_compatible_query_object_type(opts, field):
-                    raise ValueError(
-                        'Cannot use QuerySet for "%s": Use a QuerySet for "%s".' %
-                        (value.model._meta.object_name, opts.object_name)
-                    )
+            # Check that the field and the queryset use the same model in a
+            # query like .filter(author=Author.objects.all()). For example, the
+            # opts would be Author's (from the author field) and value.model
+            # would be Author.objects.all() queryset's .model (Author also).
+            # The field is the related field on the lhs side.
+            # If _forced_pk isn't set, this isn't a queryset query or values()
+            # or values_list() was specified by the developer in which case
+            # that choice is trusted.
+            if (getattr(value, '_forced_pk', False) and
+                    not check_rel_lookup_compatibility(value.model, opts, field)):
+                raise ValueError(
+                    'Cannot use QuerySet for "%s": Use a QuerySet for "%s".' %
+                    (value.model._meta.object_name, opts.object_name)
+                )
             elif hasattr(value, '_meta'):
                 self.check_query_object_type(value, opts, field)
             elif hasattr(value, '__iter__'):
@@ -2005,6 +2012,17 @@ class Query(object):
         else:
             return field.null
 
+    def as_subquery_filter(self, db):
+        self._db = db
+        self.subquery = True
+        # It's safe to drop ordering if the queryset isn't using slicing,
+        # distinct(*fields) or select_for_update().
+        if (self.low_mark == 0 and self.high_mark is None and
+                not self.distinct_fields and
+                not self.select_for_update):
+            self.clear_ordering(True)
+        return self
+
 
 def get_order_dir(field, default='ASC'):
     """

django/db/models/sql/subqueries.py

@@ -205,7 +205,5 @@ class AggregateQuery(Query):
     compiler = 'SQLAggregateCompiler'
 
     def add_subquery(self, query, using):
-        self.subquery, self.sub_params = query.get_compiler(using).as_sql(
-            with_col_aliases=True,
-            subquery=True,
-        )
+        query.subquery = True
+        self.subquery, self.sub_params = query.get_compiler(using).as_sql(with_col_aliases=True)

django/db/models/sql/where.py

@@ -197,20 +197,6 @@ class SubqueryConstraint(object):
 
     def as_sql(self, compiler, connection):
         query = self.query_object
-
-        # QuerySet was sent
-        if hasattr(query, 'values'):
-            if query._db and connection.alias != query._db:
-                raise ValueError("Can't do subqueries with queries on different DBs.")
-            # Do not override already existing values.
-            if query._fields is None:
-                query = query.values(*self.targets)
-            else:
-                query = query._clone()
-            query = query.query
-            if query.can_filter():
-                # If there is no slicing in use, then we can safely drop all ordering
-                query.clear_ordering(True)
-
+        query.set_values(self.targets)
         query_compiler = query.get_compiler(connection=connection)
         return query_compiler.as_subquery_condition(self.alias, self.columns, compiler)