Repair WithinGroup.get_children()

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

Change-Id: I563882d93c8c32292463a605b636aa60c77e9406
Fixes: #4012

1 files changed, 10 insertions, 0 deletions

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)