- reworked the way the "select_wraps_for" expression is

handled within visit_select(); this attribute was added in the
1.0 series to accommodate the subquery wrapping behavior of
SQL Server and Oracle while also working with positional
column targeting and no longer relying upon "key fallback"
in order to target columns in such a statement.  The IBM DB2
third-party dialect also has this use case, but its implementation
is using regular expressions to rewrite the textual SELECT only
and does not make use of a "wrapped" select at this time.
The logic no longer attempts to reconcile proxy set collections as
this was not deterministic, and instead assumes that the select()
and the wrapper select() match their columns postionally,
at least for the column positions they have in common,
so it is now very simple and safe.  fixes #3657.
- as a side effect of #3657 it was also revealed that the
strategy of calling upon a ResultProxy._getter was not
correctly calling into NoSuchColumnError when an expected
column was not present, and instead returned None up to
loading.instances() to produce NoneType failures; added
a raiseerr argument to _getter() which is called when we
aren't expecting None, fixes #3658.

1 files changed, 3 insertions, 7 deletions

diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index a2fc0fe68..b75dc1c07 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -1638,15 +1638,11 @@ class SQLCompiler(Compiled):
         if populate_result_map and select_wraps_for is not None:
             # if this select is a compiler-generated wrapper,
             # rewrite the targeted columns in the result map
-            wrapped_inner_columns = set(select_wraps_for.inner_columns)
+
             translate = dict(
-                (outer, inner.pop()) for outer, inner in [
-                    (
-                        outer,
-                        outer.proxy_set.intersection(wrapped_inner_columns))
-                    for outer in select.inner_columns
-                ] if inner
+                zip(select.inner_columns, select_wraps_for.inner_columns)
             )
+
             self._result_columns = [
                 (key, name, tuple(translate.get(o, o) for o in obj), type_)
                 for key, name, obj, type_ in self._result_columns