Refs #11964 -- Removed SimpleCol in favor of Query(alias_cols).

This prevent having to pass simple_col through multiple function calls
by defining whether or not references should be resolved with aliases
at the Query level.

6 files changed, 66 insertions, 94 deletions

diff --git a/django/contrib/postgres/constraints.py b/django/contrib/postgres/constraints.py
index 67e415ddcf..8cc1f58a10 100644
--- a/django/contrib/postgres/constraints.py
+++ b/django/contrib/postgres/constraints.py
@@ -38,10 +38,7 @@ class ExclusionConstraint(BaseConstraint):
         for expression, operator in self.expressions:
             if isinstance(expression, str):
                 expression = F(expression)
-            if isinstance(expression, F):
-                expression = expression.resolve_expression(query=query, simple_col=True)
-            else:
-                expression = expression.resolve_expression(query=query)
+            expression = expression.resolve_expression(query=query)
             sql, params = expression.as_sql(compiler, connection)
             expressions.append('%s WITH %s' % (sql % params, operator))
         return expressions
@@ -54,7 +51,7 @@ class ExclusionConstraint(BaseConstraint):
         return sql % tuple(schema_editor.quote_value(p) for p in params)
 
     def constraint_sql(self, model, schema_editor):
-        query = Query(model)
+        query = Query(model, alias_cols=False)
         compiler = query.get_compiler(connection=schema_editor.connection)
         expressions = self._get_expression_sql(compiler, schema_editor.connection, query)
         condition = self._get_condition_sql(compiler, schema_editor, query)
diff --git a/django/db/models/constraints.py b/django/db/models/constraints.py
index fe0d42a168..96205b44ad 100644
--- a/django/db/models/constraints.py
+++ b/django/db/models/constraints.py
@@ -33,7 +33,7 @@ class CheckConstraint(BaseConstraint):
         super().__init__(name)
 
     def _get_check_sql(self, model, schema_editor):
-        query = Query(model=model)
+        query = Query(model=model, alias_cols=False)
         where = query.build_where(self.check)
         compiler = query.get_compiler(connection=schema_editor.connection)
         sql, params = where.as_sql(compiler, schema_editor.connection)
@@ -77,7 +77,7 @@ class UniqueConstraint(BaseConstraint):
     def _get_condition_sql(self, model, schema_editor):
         if self.condition is None:
             return None
-        query = Query(model=model)
+        query = Query(model=model, alias_cols=False)
         where = query.build_where(self.condition)
         compiler = query.get_compiler(connection=schema_editor.connection)
         sql, params = where.as_sql(compiler, schema_editor.connection)
diff --git a/django/db/models/expressions.py b/django/db/models/expressions.py
index 13e0ef172c..ec7b0e67b9 100644
--- a/django/db/models/expressions.py
+++ b/django/db/models/expressions.py
@@ -529,8 +529,8 @@ class F(Combinable):
         return "{}({})".format(self.__class__.__name__, self.name)
 
     def resolve_expression(self, query=None, allow_joins=True, reuse=None,
-                           summarize=False, for_save=False, simple_col=False):
-        return query.resolve_ref(self.name, allow_joins, reuse, summarize, simple_col)
+                           summarize=False, for_save=False):
+        return query.resolve_ref(self.name, allow_joins, reuse, summarize)
 
     def asc(self, **kwargs):
         return OrderBy(self, **kwargs)
@@ -565,8 +565,7 @@ class ResolvedOuterRef(F):
 
 
 class OuterRef(F):
-    def resolve_expression(self, query=None, allow_joins=True, reuse=None,
-                           summarize=False, for_save=False, simple_col=False):
+    def resolve_expression(self, *args, **kwargs):
         if isinstance(self.name, self.__class__):
             return self.name
         return ResolvedOuterRef(self.name)
@@ -754,14 +753,19 @@ class Col(Expression):
         self.alias, self.target = alias, target
 
     def __repr__(self):
-        return "{}({}, {})".format(
-            self.__class__.__name__, self.alias, self.target)
+        alias, target = self.alias, self.target
+        identifiers = (alias, str(target)) if alias else (str(target),)
+        return '{}({})'.format(self.__class__.__name__, ', '.join(identifiers))
 
     def as_sql(self, compiler, connection):
-        qn = compiler.quote_name_unless_alias
-        return "%s.%s" % (qn(self.alias), qn(self.target.column)), []
+        alias, column = self.alias, self.target.column
+        identifiers = (alias, column) if alias else (column,)
+        sql = '.'.join(map(compiler.quote_name_unless_alias, identifiers))
+        return sql, []
 
     def relabeled_clone(self, relabels):
+        if self.alias is None:
+            return self
         return self.__class__(relabels.get(self.alias, self.alias), self.target, self.output_field)
 
     def get_group_by_cols(self, alias=None):
@@ -774,40 +778,6 @@ class Col(Expression):
                 self.target.get_db_converters(connection))
 
 
-class SimpleCol(Expression):
-    """
-    Represents the SQL of a column name without the table name.
-
-    This variant of Col doesn't include the table name (or an alias) to
-    avoid a syntax error in check constraints.
-    """
-    contains_column_references = True
-
-    def __init__(self, target, output_field=None):
-        if output_field is None:
-            output_field = target
-        super().__init__(output_field=output_field)
-        self.target = target
-
-    def __repr__(self):
-        return '{}({})'.format(self.__class__.__name__, self.target)
-
-    def as_sql(self, compiler, connection):
-        qn = compiler.quote_name_unless_alias
-        return qn(self.target.column), []
-
-    def get_group_by_cols(self, alias=None):
-        return [self]
-
-    def get_db_converters(self, connection):
-        if self.target == self.output_field:
-            return self.output_field.get_db_converters(connection)
-        return (
-            self.output_field.get_db_converters(connection) +
-            self.target.get_db_converters(connection)
-        )
-
-
 class Ref(Expression):
     """
     Reference to column alias of the query. For example, Ref('sum_cost') in
diff --git a/django/db/models/indexes.py b/django/db/models/indexes.py
index 49f4989462..77a8423ef8 100644
--- a/django/db/models/indexes.py
+++ b/django/db/models/indexes.py
@@ -40,7 +40,7 @@ class Index:
     def _get_condition_sql(self, model, schema_editor):
         if self.condition is None:
             return None
-        query = Query(model=model)
+        query = Query(model=model, alias_cols=False)
         where = query.build_where(self.condition)
         compiler = query.get_compiler(connection=schema_editor.connection)
         sql, params = where.as_sql(compiler, schema_editor.connection)
diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py
index dd5889625f..e6803649e7 100644
--- a/django/db/models/sql/query.py
+++ b/django/db/models/sql/query.py
@@ -23,9 +23,7 @@ from django.core.exceptions import (
 from django.db import DEFAULT_DB_ALIAS, NotSupportedError, connections
 from django.db.models.aggregates import Count
 from django.db.models.constants import LOOKUP_SEP
-from django.db.models.expressions import (
-    BaseExpression, Col, F, OuterRef, Ref, SimpleCol,
-)
+from django.db.models.expressions import BaseExpression, Col, F, OuterRef, Ref
 from django.db.models.fields import Field
 from django.db.models.fields.related_lookups import MultiColSource
 from django.db.models.lookups import Lookup
@@ -69,12 +67,6 @@ JoinInfo = namedtuple(
 )
 
 
-def _get_col(target, field, alias, simple_col):
-    if simple_col:
-        return SimpleCol(target, field)
-    return target.get_col(alias, field)
-
-
 class RawQuery:
     """A single raw SQL query."""
 
@@ -151,7 +143,7 @@ class Query(BaseExpression):
 
     compiler = 'SQLCompiler'
 
-    def __init__(self, model, where=WhereNode):
+    def __init__(self, model, where=WhereNode, alias_cols=True):
         self.model = model
         self.alias_refcount = {}
         # alias_map is the most important data structure regarding joins.
@@ -160,6 +152,8 @@ class Query(BaseExpression):
         # the table name) and the value is a Join-like object (see
         # sql.datastructures.Join for more information).
         self.alias_map = {}
+        # Whether to provide alias to columns during reference resolving.
+        self.alias_cols = alias_cols
         # Sometimes the query contains references to aliases in outer queries (as
         # a result of split_exclude). Correct alias quoting needs to know these
         # aliases too.
@@ -360,6 +354,11 @@ class Query(BaseExpression):
         clone.change_aliases(change_map)
         return clone
 
+    def _get_col(self, target, field, alias):
+        if not self.alias_cols:
+            alias = None
+        return target.get_col(alias, field)
+
     def rewrite_cols(self, annotation, col_cnt):
         # We must make sure the inner query has the referred columns in it.
         # If we are aggregating over an annotation, then Django uses Ref()
@@ -1050,17 +1049,16 @@ class Query(BaseExpression):
             sql = '(%s)' % sql
         return sql, params
 
-    def resolve_lookup_value(self, value, can_reuse, allow_joins, simple_col):
+    def resolve_lookup_value(self, value, can_reuse, allow_joins):
         if hasattr(value, 'resolve_expression'):
-            kwargs = {'reuse': can_reuse, 'allow_joins': allow_joins}
-            if isinstance(value, F):
-                kwargs['simple_col'] = simple_col
-            value = value.resolve_expression(self, **kwargs)
+            value = value.resolve_expression(
+                self, reuse=can_reuse, allow_joins=allow_joins,
+            )
         elif isinstance(value, (list, tuple)):
             # The items of the iterable may be expressions and therefore need
             # to be resolved independently.
             return type(value)(
-                self.resolve_lookup_value(sub_value, can_reuse, allow_joins, simple_col)
+                self.resolve_lookup_value(sub_value, can_reuse, allow_joins)
                 for sub_value in value
             )
         return value
@@ -1192,7 +1190,7 @@ class Query(BaseExpression):
 
     def build_filter(self, filter_expr, branch_negated=False, current_negated=False,
                      can_reuse=None, allow_joins=True, split_subq=True,
-                     reuse_with_filtered_relation=False, simple_col=False):
+                     reuse_with_filtered_relation=False):
         """
         Build a WhereNode for a single filter clause but don't add it
         to this Query. Query.add_q() will then add this filter to the where
@@ -1244,7 +1242,7 @@ class Query(BaseExpression):
             raise FieldError("Joined field references are not permitted in this query")
 
         pre_joins = self.alias_refcount.copy()
-        value = self.resolve_lookup_value(value, can_reuse, allow_joins, simple_col)
+        value = self.resolve_lookup_value(value, can_reuse, allow_joins)
         used_joins = {k for k, v in self.alias_refcount.items() if v > pre_joins.get(k, 0)}
 
         self.check_filterable(value)
@@ -1289,11 +1287,11 @@ class Query(BaseExpression):
             if num_lookups > 1:
                 raise FieldError('Related Field got invalid lookup: {}'.format(lookups[0]))
             if len(targets) == 1:
-                col = _get_col(targets[0], join_info.final_field, alias, simple_col)
+                col = self._get_col(targets[0], join_info.final_field, alias)
             else:
                 col = MultiColSource(alias, targets, join_info.targets, join_info.final_field)
         else:
-            col = _get_col(targets[0], join_info.final_field, alias, simple_col)
+            col = self._get_col(targets[0], join_info.final_field, alias)
 
         condition = self.build_lookup(lookups, col, value)
         lookup_type = condition.lookup_name
@@ -1315,7 +1313,7 @@ class Query(BaseExpression):
                 #   <=>
                 # NOT (col IS NOT NULL AND col = someval).
                 lookup_class = targets[0].get_lookup('isnull')
-                col = _get_col(targets[0], join_info.targets[0], alias, simple_col)
+                col = self._get_col(targets[0], join_info.targets[0], alias)
                 clause.add(lookup_class(col, False), AND)
         return clause, used_joins if not require_outer else ()
 
@@ -1340,11 +1338,10 @@ class Query(BaseExpression):
         self.demote_joins(existing_inner)
 
     def build_where(self, q_object):
-        return self._add_q(q_object, used_aliases=set(), allow_joins=False, simple_col=True)[0]
+        return self._add_q(q_object, used_aliases=set(), allow_joins=False)[0]
 
     def _add_q(self, q_object, used_aliases, branch_negated=False,
-               current_negated=False, allow_joins=True, split_subq=True,
-               simple_col=False):
+               current_negated=False, allow_joins=True, split_subq=True):
         """Add a Q-object to the current filter."""
         connector = q_object.connector
         current_negated = current_negated ^ q_object.negated
@@ -1356,13 +1353,13 @@ class Query(BaseExpression):
             if isinstance(child, Node):
                 child_clause, needed_inner = self._add_q(
                     child, used_aliases, branch_negated,
-                    current_negated, allow_joins, split_subq, simple_col)
+                    current_negated, allow_joins, split_subq)
                 joinpromoter.add_votes(needed_inner)
             else:
                 child_clause, needed_inner = self.build_filter(
                     child, can_reuse=used_aliases, branch_negated=branch_negated,
                     current_negated=current_negated, allow_joins=allow_joins,
-                    split_subq=split_subq, simple_col=simple_col,
+                    split_subq=split_subq,
                 )
                 joinpromoter.add_votes(needed_inner)
             if child_clause:
@@ -1639,7 +1636,7 @@ class Query(BaseExpression):
             else:
                 yield from cls._gen_col_aliases(expr.get_source_expressions())
 
-    def resolve_ref(self, name, allow_joins=True, reuse=None, summarize=False, simple_col=False):
+    def resolve_ref(self, name, allow_joins=True, reuse=None, summarize=False):
         if not allow_joins and LOOKUP_SEP in name:
             raise FieldError("Joined field references are not permitted in this query")
         annotation = self.annotations.get(name)
@@ -1673,8 +1670,7 @@ class Query(BaseExpression):
             join_info.transform_function(targets[0], final_alias)
             if reuse is not None:
                 reuse.update(join_list)
-            col = _get_col(targets[0], join_info.targets[0], join_list[-1], simple_col)
-            return col
+            return self._get_col(targets[0], join_info.targets[0], join_list[-1])
 
     def split_exclude(self, filter_expr, can_reuse, names_with_path):
         """
diff --git a/tests/queries/test_query.py b/tests/queries/test_query.py
index 012d56a02f..ecd9c96d8c 100644
--- a/tests/queries/test_query.py
+++ b/tests/queries/test_query.py
@@ -2,7 +2,7 @@ from datetime import datetime
 
 from django.core.exceptions import FieldError
 from django.db.models import CharField, F, Q
-from django.db.models.expressions import SimpleCol
+from django.db.models.expressions import Col
 from django.db.models.fields.related_lookups import RelatedIsNull
 from django.db.models.functions import Lower
 from django.db.models.lookups import Exact, GreaterThan, IsNull, LessThan
@@ -23,20 +23,24 @@ class TestQuery(SimpleTestCase):
         self.assertEqual(lookup.rhs, 2)
         self.assertEqual(lookup.lhs.target, Author._meta.get_field('num'))
 
-    def test_simplecol_query(self):
-        query = Query(Author)
+    def test_non_alias_cols_query(self):
+        query = Query(Author, alias_cols=False)
         where = query.build_where(Q(num__gt=2, name__isnull=False) | Q(num__lt=F('id')))
 
         name_isnull_lookup, num_gt_lookup = where.children[0].children
         self.assertIsInstance(num_gt_lookup, GreaterThan)
-        self.assertIsInstance(num_gt_lookup.lhs, SimpleCol)
+        self.assertIsInstance(num_gt_lookup.lhs, Col)
+        self.assertIsNone(num_gt_lookup.lhs.alias)
         self.assertIsInstance(name_isnull_lookup, IsNull)
-        self.assertIsInstance(name_isnull_lookup.lhs, SimpleCol)
+        self.assertIsInstance(name_isnull_lookup.lhs, Col)
+        self.assertIsNone(name_isnull_lookup.lhs.alias)
 
         num_lt_lookup = where.children[1]
         self.assertIsInstance(num_lt_lookup, LessThan)
-        self.assertIsInstance(num_lt_lookup.rhs, SimpleCol)
-        self.assertIsInstance(num_lt_lookup.lhs, SimpleCol)
+        self.assertIsInstance(num_lt_lookup.rhs, Col)
+        self.assertIsNone(num_lt_lookup.rhs.alias)
+        self.assertIsInstance(num_lt_lookup.lhs, Col)
+        self.assertIsNone(num_lt_lookup.lhs.alias)
 
     def test_complex_query(self):
         query = Query(Author)
@@ -54,23 +58,26 @@ class TestQuery(SimpleTestCase):
         self.assertEqual(lookup.lhs.target, Author._meta.get_field('num'))
 
     def test_multiple_fields(self):
-        query = Query(Item)
+        query = Query(Item, alias_cols=False)
         where = query.build_where(Q(modified__gt=F('created')))
         lookup = where.children[0]
         self.assertIsInstance(lookup, GreaterThan)
-        self.assertIsInstance(lookup.rhs, SimpleCol)
-        self.assertIsInstance(lookup.lhs, SimpleCol)
+        self.assertIsInstance(lookup.rhs, Col)
+        self.assertIsNone(lookup.rhs.alias)
+        self.assertIsInstance(lookup.lhs, Col)
+        self.assertIsNone(lookup.lhs.alias)
         self.assertEqual(lookup.rhs.target, Item._meta.get_field('created'))
         self.assertEqual(lookup.lhs.target, Item._meta.get_field('modified'))
 
     def test_transform(self):
-        query = Query(Author)
+        query = Query(Author, alias_cols=False)
         with register_lookup(CharField, Lower):
             where = query.build_where(~Q(name__lower='foo'))
         lookup = where.children[0]
         self.assertIsInstance(lookup, Exact)
         self.assertIsInstance(lookup.lhs, Lower)
-        self.assertIsInstance(lookup.lhs.lhs, SimpleCol)
+        self.assertIsInstance(lookup.lhs.lhs, Col)
+        self.assertIsNone(lookup.lhs.lhs.alias)
         self.assertEqual(lookup.lhs.lhs.target, Author._meta.get_field('name'))
 
     def test_negated_nullable(self):
@@ -96,15 +103,17 @@ class TestQuery(SimpleTestCase):
             query.build_where(Q(rank__gt=F('author__num')))
 
     def test_foreign_key_exclusive(self):
-        query = Query(ObjectC)
+        query = Query(ObjectC, alias_cols=False)
         where = query.build_where(Q(objecta=None) | Q(objectb=None))
         a_isnull = where.children[0]
         self.assertIsInstance(a_isnull, RelatedIsNull)
-        self.assertIsInstance(a_isnull.lhs, SimpleCol)
+        self.assertIsInstance(a_isnull.lhs, Col)
+        self.assertIsNone(a_isnull.lhs.alias)
         self.assertEqual(a_isnull.lhs.target, ObjectC._meta.get_field('objecta'))
         b_isnull = where.children[1]
         self.assertIsInstance(b_isnull, RelatedIsNull)
-        self.assertIsInstance(b_isnull.lhs, SimpleCol)
+        self.assertIsInstance(b_isnull.lhs, Col)
+        self.assertIsNone(b_isnull.lhs.alias)
         self.assertEqual(b_isnull.lhs.target, ObjectC._meta.get_field('objectb'))
 
     def test_clone_select_related(self):