- Added a new directive used within the scope of an attribute "set" operation

to disable autoflush, in the case that the attribute needs to lazy-load
the "old" value, as in when replacing one-to-one values or some
kinds of many-to-one.  A flush at this point otherwise occurs
at the point that the attribute is None and can cause NULL violations.
[ticket:2921]

3 files changed, 9 insertions, 3 deletions

diff --git a/lib/sqlalchemy/orm/attributes.py b/lib/sqlalchemy/orm/attributes.py
index e5f8550ab..7647bf9d0 100644
--- a/lib/sqlalchemy/orm/attributes.py
+++ b/lib/sqlalchemy/orm/attributes.py
@@ -23,7 +23,7 @@ from .base import PASSIVE_NO_RESULT, ATTR_WAS_SET, ATTR_EMPTY, NO_VALUE,\
             NEVER_SET, NO_CHANGE, CALLABLES_OK, SQL_OK, RELATED_OBJECT_OK,\
             INIT_OK, NON_PERSISTENT_OK, LOAD_AGAINST_COMMITTED, PASSIVE_OFF,\
             PASSIVE_RETURN_NEVER_SET, PASSIVE_NO_INITIALIZE, PASSIVE_NO_FETCH,\
-            PASSIVE_NO_FETCH_RELATED, PASSIVE_ONLY_PERSISTENT
+            PASSIVE_NO_FETCH_RELATED, PASSIVE_ONLY_PERSISTENT, NO_AUTOFLUSH
 from .base import state_str, instance_str
 
 @inspection._self_inspects
@@ -761,7 +761,7 @@ class ScalarObjectAttributeImpl(ScalarAttributeImpl):
 
         """
         if self.dispatch._active_history:
-            old = self.get(state, dict_, passive=PASSIVE_ONLY_PERSISTENT)
+            old = self.get(state, dict_, passive=PASSIVE_ONLY_PERSISTENT | NO_AUTOFLUSH)
         else:
             old = self.get(state, dict_, passive=PASSIVE_NO_FETCH)
 
diff --git a/lib/sqlalchemy/orm/base.py b/lib/sqlalchemy/orm/base.py
index 577f9ff76..e973de897 100644
--- a/lib/sqlalchemy/orm/base.py
+++ b/lib/sqlalchemy/orm/base.py
@@ -80,6 +80,10 @@ LOAD_AGAINST_COMMITTED = util.symbol("LOAD_AGAINST_COMMITTED",
 """, canonical=32
 )
 
+NO_AUTOFLUSH = util.symbol("NO_AUTOFLUSH",
+"""loader callables should disable autoflush.
+""", canonical=64)
+
 # pre-packaged sets of flags used as inputs
 PASSIVE_OFF = util.symbol("PASSIVE_OFF",
     "Callables can be emitted in all cases.",
diff --git a/lib/sqlalchemy/orm/strategies.py b/lib/sqlalchemy/orm/strategies.py
index bd9b02d24..2c18e8129 100644
--- a/lib/sqlalchemy/orm/strategies.py
+++ b/lib/sqlalchemy/orm/strategies.py
@@ -536,9 +536,10 @@ class LazyLoader(AbstractRelationshipLoader):
         pending = not state.key
 
         # don't autoflush on pending
-        if pending:
+        if pending or passive & attributes.NO_AUTOFLUSH:
             q = q.autoflush(False)
 
+
         if state.load_path:
             q = q._with_current_path(state.load_path[self.parent_property])
 
@@ -568,6 +569,7 @@ class LazyLoader(AbstractRelationshipLoader):
 
         q = q.filter(lazy_clause)
 
+
         result = q.all()
         if self.uselist:
             return result