allow serialization of dal.py/DAL

gluon/dal.py

@@ -14,7 +14,7 @@ from pydal import DAL as pyDAL
 from pydal import Field
 from pydal.objects import Row, Rows, Table, Query, Expression
 from pydal import SQLCustomType, geoPoint, geoLine, geoPolygon
-
+import copy_reg as copyreg
 
 def _default_validators(db, field):
     """
@@ -97,6 +97,15 @@ class DAL(pyDAL):
     Field = Field
     Table = Table
 
+def DAL_unpickler(db_uid):
+    return DAL('<zombie>', db_uid=db_uid)
+
+
+def DAL_pickler(db):
+    return DAL_unpickler, (db._db_uid,)
+
+copyreg.pickle(DAL, DAL_pickler, DAL_unpickler)
+
 #: add web2py contrib drivers to pyDAL
 from pydal.drivers import DRIVERS
 if not DRIVERS.get('pymysql'):