Create a real type for Tuple() and handle appropriately in compiler

Improved the :func:`_sql.tuple_` construct such that it behaves predictably
when used in a columns-clause context.  The SQL tuple is not supported as a
"SELECT" columns clause element on most backends; on those that do
(PostgreSQL, not surprisingly), the Python DBAPI does not have a "nested
type" concept so there are still challenges in fetching rows for such an
object. Use of :func:`_sql.tuple_` in a :func:`_sql.select` or
:class:`_orm.Query` will now raise a :class:`_exc.CompileError` at the
point at which the :func:`_sql.tuple_` object is seen as presenting itself
for fetching rows (i.e., if the tuple is in the columns clause of a
subquery, no error is raised).  For ORM use,the :class:`_orm.Bundle` object
is an explicit directive that a series of columns should be returned as a
sub-tuple per row and is suggested by the error message. Additionally ,the
tuple will now render with parenthesis in all contexts. Previously, the
parenthesization would not render in a columns context leading to
non-defined behavior.

As part of this change, Tuple receives a dedicated datatype
which appears to allow us the very desirable change of removing
the bindparam._expanding_in_types attribute as well as
ClauseList._tuple_values (which might already have not been
needed due to #4645).

Fixes: #5127
Change-Id: Iecafa0e0aac2f1f37ec8d0e1631d562611c90200

1 files changed, 3 insertions, 2 deletions

diff --git a/test/sql/test_operators.py b/test/sql/test_operators.py
index 7a027e28a..e5835a749 100644
--- a/test/sql/test_operators.py
+++ b/test/sql/test_operators.py
@@ -2791,7 +2791,7 @@ class TupleTypingTest(fixtures.TestBase):
         )
         t1 = tuple_(a, b, c)
         expr = t1 == (3, "hi", "there")
-        self._assert_types([bind.type for bind in expr.right.element.clauses])
+        self._assert_types([bind.type for bind in expr.right.clauses])
 
     def test_type_coercion_on_in(self):
         a, b, c = (
@@ -2803,7 +2803,8 @@ class TupleTypingTest(fixtures.TestBase):
         expr = t1.in_([(3, "hi", "there"), (4, "Q", "P")])
 
         eq_(len(expr.right.value), 2)
-        self._assert_types(expr.right._expanding_in_types)
+
+        self._assert_types(expr.right.type.types)
 
 
 class InSelectableTest(fixtures.TestBase, testing.AssertsCompiledSQL):