ERP5Type.Base: .serialize() is possible without writing object to DB

There is no need to write object to DB just to make sure it stays the
same - since ZODB 3.10 there is explicit way to constraint commit to
succeed only if an object does not change[1] :

    Connection.readCurrent(obj)

All FileStorage [2], ZEO [3] and NEO [4,5] should support this.

[1] https://github.com/zopefoundation/ZODB/commit/5a9afb14
[2] https://github.com/zopefoundation/ZODB/commit/99cbe353
[3] https://github.com/zopefoundation/ZODB/commit/a3de2ce8
[4] http://git.erp5.org/gitweb/neoppod.git/commitdiff/af5253bd
[5] http://git.erp5.org/gitweb/neoppod.git/commitdiff/40652c1c

/cc @vpelletier, @jm

product/ERP5Type/Base.py

@@ -3262,7 +3262,14 @@ class Base( CopyContainer,
   def serialize(self):
     """Make the transaction accessing to this object atomic
     """
-    self._p_changed = 1
+    # we don't have anything to do if this is a newly created object, never
+    # committed and thus not yet registered to Connection - if it is reachable
+    # from database root, the object will be stored to database on commit.
+    if self._p_jar is None:
+        return
+
+    # ask ZODB to make sure the object stays unchanged at commit
+    self._p_jar.readCurrent(self)
 
   # Helpers
   def getQuantityPrecisionFromResource(self, resource, d=2):