- fix to "row switch" behavior, i.e. when an INSERT/DELETE is combined into a

  single UPDATE; many-to-many relations on the parent object update properly.
  [ticket:841]
- it's an error to session.save() an object which is already persistent
  [ticket:840]
- changed a bunch of repr(obj) calls in session.py exceptions to use mapperutil.instance_str()

3 files changed, 21 insertions, 11 deletions

diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
index 2f3c36515..94ef04300 100644
--- a/lib/sqlalchemy/orm/mapper.py
+++ b/lib/sqlalchemy/orm/mapper.py
@@ -968,7 +968,7 @@ class Mapper(object):
                     raise exceptions.FlushError("New instance %s with identity key %s conflicts with persistent instance %s" % (mapperutil.instance_str(obj), str(instance_key), mapperutil.instance_str(existing)))
                 if self.__should_log_debug:
                     self.__log_debug("detected row switch for identity %s.  will update %s, remove %s from transaction" % (instance_key, mapperutil.instance_str(obj), mapperutil.instance_str(existing)))
-                uowtransaction.unregister_object(existing)
+                uowtransaction.set_row_switch(existing)
             if has_identity(obj):
                 if obj._instance_key != instance_key:
                     raise exceptions.FlushError("Can't change the identity of instance %s in session (existing identity: %s; new identity: %s)" % (mapperutil.instance_str(obj), obj._instance_key, instance_key))
diff --git a/lib/sqlalchemy/orm/session.py b/lib/sqlalchemy/orm/session.py
index 04aaa1209..42ad30b6a 100644
--- a/lib/sqlalchemy/orm/session.py
+++ b/lib/sqlalchemy/orm/session.py
@@ -631,6 +631,8 @@ class Session(object):
                         
         if self.bind is not None:
             return self.bind
+        elif mapper is None:
+            raise exceptions.InvalidRequestError("Could not locate any mapper associated with SQL expression")
         else:
             if isinstance(mapper, type):
                 mapper = _class_mapper(mapper)
@@ -721,7 +723,7 @@ class Session(object):
 
         self._validate_persistent(obj)
         if self.query(obj.__class__)._get(obj._instance_key, reload=True) is None:
-            raise exceptions.InvalidRequestError("Could not refresh instance '%s'" % repr(obj))
+            raise exceptions.InvalidRequestError("Could not refresh instance '%s'" % mapperutil.instance_str(obj))
 
     def expire(self, obj):
         """Mark the given object as expired.
@@ -753,7 +755,7 @@ class Session(object):
 
         def exp():
             if self.query(obj.__class__)._get(obj._instance_key, reload=True) is None:
-                raise exceptions.InvalidRequestError("Could not refresh instance '%s'" % repr(obj))
+                raise exceptions.InvalidRequestError("Could not refresh instance '%s'" % mapperutil.instance_str(obj))
 
         attribute_manager.trigger_history(obj, exp)
 
@@ -954,10 +956,7 @@ class Session(object):
     
     def _save_impl(self, obj, **kwargs):
         if hasattr(obj, '_instance_key'):
-            if obj._instance_key not in self.identity_map:
-                raise exceptions.InvalidRequestError("Instance '%s' is a detached instance "
-                                                     "or is already persistent in a "
-                                                     "different Session" % repr(obj))
+            raise exceptions.InvalidRequestError("Instance '%s' is already persistent" % mapperutil.instance_str(obj))
         else:
             # TODO: consolidate the steps here
             attribute_manager.manage(obj)
@@ -969,7 +968,7 @@ class Session(object):
         if self._is_attached(obj) and obj not in self.deleted:
             return
         if not hasattr(obj, '_instance_key'):
-            raise exceptions.InvalidRequestError("Instance '%s' is not persisted" % repr(obj))
+            raise exceptions.InvalidRequestError("Instance '%s' is not persisted" % mapperutil.instance_str(obj))
         self._attach(obj)
 
     def _register_persistent(self, obj):
@@ -983,7 +982,7 @@ class Session(object):
             if old_id is not None and old_id in _sessions:
                 raise exceptions.InvalidRequestError("Object '%s' is already attached "
                                                      "to session '%s' (this is '%s')" %
-                                                     (repr(obj), old_id, id(self)))
+                                                     (mapperutil.instance_str(obj), old_id, id(self)))
 
                 # auto-removal from the old session is disabled.  but if we decide to
                 # turn it back on, do it as below: gingerly since _sessions is a WeakValueDict
@@ -1001,7 +1000,7 @@ class Session(object):
 
     def _unattach(self, obj):
         if not self._is_attached(obj):
-            raise exceptions.InvalidRequestError("Instance '%s' not attached to this Session" % repr(obj))
+            raise exceptions.InvalidRequestError("Instance '%s' not attached to this Session" % mapperutil.instance_str(obj))
         del obj._sa_session_id
 
     def _validate_persistent(self, obj):
diff --git a/lib/sqlalchemy/orm/unitofwork.py b/lib/sqlalchemy/orm/unitofwork.py
index 7a443b331..43f0d46d9 100644
--- a/lib/sqlalchemy/orm/unitofwork.py
+++ b/lib/sqlalchemy/orm/unitofwork.py
@@ -304,6 +304,17 @@ class UOWTransaction(object):
 
         task.append(obj, listonly, isdelete=isdelete, **kwargs)
 
+    def set_row_switch(self, obj):
+        """mark a deleted object as a 'row switch'.
+        
+        this indicates that an INSERT statement elsewhere corresponds to this DELETE;
+        the INSERT is converted to an UPDATE and the DELETE does not occur.
+        """
+        mapper = object_mapper(obj)
+        task = self.get_task_by_mapper(mapper)
+        taskelement = task._objects[obj]
+        taskelement.isdelete = "rowswitch"
+        
     def unregister_object(self, obj):
         """remove an object from its parent UOWTask.
         
@@ -902,7 +913,7 @@ class UOWTaskElement(object):
         self.childtasks = []
         self.__isdelete = False
         self.__preprocessed = {}
-
+        
     def _get_listonly(self):
         return self.__listonly