Reimplement .compare() in terms of a visitor

Reworked the :meth:`.ClauseElement.compare` methods in terms of a new
visitor-based approach, and additionally added test coverage ensuring that
all :class:`.ClauseElement` subclasses can be accurately compared
against each other in terms of structure.   Structural comparison
capability is used to a small degree within the ORM currently, however
it also may form the basis for new caching features.

Fixes: #4336
Change-Id: I581b667d8e1642a6c27165cc9f4aded1c66effc6

1 files changed, 9 insertions, 0 deletions

diff --git a/lib/sqlalchemy/sql/selectable.py b/lib/sqlalchemy/sql/selectable.py
index d4528f0c3..796e2b272 100644
--- a/lib/sqlalchemy/sql/selectable.py
+++ b/lib/sqlalchemy/sql/selectable.py
@@ -1994,6 +1994,9 @@ class ForUpdateArg(ClauseElement):
             and other.of is self.of
         )
 
+    def __ne__(self, other):
+        return not self.__eq__(other)
+
     def __hash__(self):
         return id(self)
 
@@ -3941,6 +3944,12 @@ class TextAsFrom(SelectBase):
         self._reset_exported()
         self.element = clone(self.element, **kw)
 
+    def get_children(self, column_collections=True, **kw):
+        if column_collections:
+            for c in self.column_args:
+                yield c
+        yield self.element
+
     def _scalar_type(self):
         return self.column_args[0].type