.

bigfile/_file_zodb.pyx

@@ -153,20 +153,27 @@ class ZSync:
         zsync.zconn = zconn     # XXX -> weakref
         zsync.wconn = wconn
 
-        # when connection will be reopened -> zsync.on_connection_open()
-        zconn.onOpenCallback(zsync)
+        # NOTE zcon.onOpenCallback is not enought: zconn.at can change even
+        # without zconn.close/zconn.open, e.g.:
+        # zconn = DB.open(transaction_manager=tm)
+        # tm.commit()   # zconn.at updated          (zconn.afterCompletion -> zconn.newTransaction)
+        # tm.commit()   # zconn.at updated again
+        #
+        # TODO test for that.
+        #zconn.onOpenCallback(zsync)
+        zconn.onResyncCallback(zsync)
 
+    """
     # DB.open() pops .zconn from connection pool and "opens" for usage.
     # -> resync .wconn to new database view of ZODB connection.
     #
-    # FIXME zconn.at can change even without zconn.close/zconn.open, e.g.:
-    # zconn = DB.open(transaction_manager=tm)
-    # tm.commit()   # zconn.at updated          (zconn.afterCompletion -> zconn.newTransaction)
-    # tm.commit()   # zconn.at updated again
-    #
-    # TODO fix/test for that.
     def on_connection_open(zsync):
         print('ZSync.resync %r %r' % (zsync.zconn, zsync.wconn))
         zsync.wconn.resync(zconn_at(zsync.zconn))
+    """
+
+    def on_connection_resync(zsync):
+        print('ZSync.resync %r %r' % (zsync.zconn, zsync.wconn))
+        zsync.wconn.resync(zconn_at(zsync.zconn))
 
     # TODO zconn dealloc -> wconn.close

lib/zodb.py

@@ -24,6 +24,7 @@ from ZODB.FileStorage import FileStorage
 from ZODB import DB
 from ZODB.utils import p64, u64
 from persistent import Persistent
+from weakref import WeakSet
 import gc
 
 import pkg_resources
@@ -192,3 +193,35 @@ def _zmajor():
 
 # zmajor is set to major ZODB version.
 zmajor = _zmajor()
+
+
+
+# patch for ZODB.Connection to support callback on after database view is changed
+ZODB.Connection.Connection._onResyncCallbacks = None
+def Connection_onResyncCallback(self, f):
+    if self._onResyncCallbacks is None:
+        # NOTE WeakSet does not work for bound methods - they are always created
+        # anew for each obj.method access, and thus will go away almost immediately
+        self._onResyncCallbacks = WeakSet()
+
+assert not hasattr(ZODB.Connection.Connection, 'onResyncCallback')
+ZODB.Connection.Connection.onResyncCallback = Connection_onResyncCallback
+
+# ZODB5: hook into Connection.newTransaction        XXX .newTransaction .afterCompletion ?
+# ZODB4: hook into Connection._storage_sync         XXX .newTransaction .afterCompletion ?
+# ZODB3: TODO
+# XXX ZODB5 only for now
+# XXX ERP5Type/patches/ZODBConnection.py overrides newTransaction without calling orig_newTransaction
+#     -> fix it there.
+_orig_Connection_newTransaction = ZODB.Connection.Connection.newTransaction
+def _ZConnection_newTransaction(self, transaction, sync=True):
+    _orig_Connection_newTransaction(self, transaction, sync)
+
+    # FIXME method name hardcoded. Better not do it and allow f to be general
+    # callable, but that does not work with bound method - see above.
+    # ( Something like WeakMethod from py3 could help )
+    if self._onResyncCallbacks:
+        for f in self._onResyncCallbacks:
+            f.on_connection_resync()
+
+ZODB.Connection.Connection.newTransaction = _ZConnection_newTransaction