Fixed bug where using server_onupdate=<FetchedValue|DefaultClause>

without passing the "for_update=True" flag would apply the default
object to the server_default, blowing away whatever was there.
The explicit for_update=True argument shouldn't be needed with this usage
(especially since the documentation shows an example without it being
used) so it is now arranged internally using a copy of the given default
object, if the flag isn't set to what corresponds to that argument.
Also in 0.7.10. [ticket:2631]

1 files changed, 15 insertions, 2 deletions

diff --git a/lib/sqlalchemy/schema.py b/lib/sqlalchemy/schema.py
index 4f3655a1d..553936299 100644
--- a/lib/sqlalchemy/schema.py
+++ b/lib/sqlalchemy/schema.py
@@ -945,7 +945,7 @@ class Column(SchemaItem, expression.ColumnClause):
 
         if self.server_default is not None:
             if isinstance(self.server_default, FetchedValue):
-                args.append(self.server_default)
+                args.append(self.server_default._as_for_update(False))
             else:
                 args.append(DefaultClause(self.server_default))
 
@@ -957,7 +957,7 @@ class Column(SchemaItem, expression.ColumnClause):
 
         if self.server_onupdate is not None:
             if isinstance(self.server_onupdate, FetchedValue):
-                args.append(self.server_onupdate)
+                args.append(self.server_onupdate._as_for_update(True))
             else:
                 args.append(DefaultClause(self.server_onupdate,
                                             for_update=True))
@@ -1854,6 +1854,19 @@ class FetchedValue(_NotAColumnExpr, events.SchemaEventTarget):
     def __init__(self, for_update=False):
         self.for_update = for_update
 
+    def _as_for_update(self, for_update):
+        if for_update == self.for_update:
+            return self
+        else:
+            return self._clone(for_update)
+
+    def _clone(self, for_update):
+        n = self.__class__.__new__(self.__class__)
+        n.__dict__.update(self.__dict__)
+        n.__dict__.pop('column', None)
+        n.for_update = for_update
+        return n
+
     def _set_parent(self, column):
         self.column = column
         if self.for_update: