Repair WithinGroup.get_children()

Fixed AttributeError which would occur in :class:`.WithinGroup`
construct during an iteration of the structure.

Change-Id: I563882d93c8c32292463a605b636aa60c77e9406
Fixes: #4012

3 files changed, 19 insertions, 1 deletions

diff --git a/doc/build/changelog/changelog_11.rst b/doc/build/changelog/changelog_11.rst
index 612dda08a..071cf074e 100644
--- a/doc/build/changelog/changelog_11.rst
+++ b/doc/build/changelog/changelog_11.rst
@@ -21,6 +21,14 @@
 .. changelog::
     :version: 1.1.11
 
+    .. change:: 4012
+        :tags: bug, sql
+        :tickets: 4012
+        :versions: 1.2.0b1
+
+        Fixed AttributeError which would occur in :class:`.WithinGroup`
+        construct during an iteration of the structure.
+
     .. change:: 4005
         :tags: bug, postgresql
         :tickets: 4005
diff --git a/lib/sqlalchemy/sql/elements.py b/lib/sqlalchemy/sql/elements.py
index 88c294999..46a8d2c35 100644
--- a/lib/sqlalchemy/sql/elements.py
+++ b/lib/sqlalchemy/sql/elements.py
@@ -3379,7 +3379,7 @@ class WithinGroup(ColumnElement):
 
     def get_children(self, **kwargs):
         return [c for c in
-                (self.func, self.order_by)
+                (self.element, self.order_by)
                 if c is not None]
 
     def _copy_internals(self, clone=_clone, **kw):
diff --git a/test/sql/test_generative.py b/test/sql/test_generative.py
index 1a12a8b0e..9474560ff 100644
--- a/test/sql/test_generative.py
+++ b/test/sql/test_generative.py
@@ -8,6 +8,7 @@ from sqlalchemy.testing import fixtures, AssertsExecutionResults, \
 from sqlalchemy import testing
 from sqlalchemy.sql.visitors import ClauseVisitor, CloningVisitor, \
     cloned_traverse, ReplacingCloningVisitor
+from sqlalchemy.sql import visitors
 from sqlalchemy import exc
 from sqlalchemy.sql import util as sql_util
 from sqlalchemy.testing import (eq_,
@@ -594,6 +595,15 @@ class ClauseTest(fixtures.TestBase, AssertsCompiledSQL):
         expr2 = CloningVisitor().traverse(expr)
         assert str(expr) == str(expr2)
 
+        assert expr in visitors.iterate(expr, {})
+
+    def test_within_group(self):
+        expr = func.row_number().within_group(t1.c.col1)
+        expr2 = CloningVisitor().traverse(expr)
+        assert str(expr) == str(expr2)
+
+        assert expr in visitors.iterate(expr, {})
+
     def test_funcfilter(self):
         expr = func.count(1).filter(t1.c.col1 > 1)
         expr2 = CloningVisitor().traverse(expr)