[ovs-dev] [PATCH] Allow subclasses of Idl to define a notification hook

[Terry Wilson]

It is useful to make the notification events that Idl processes
accessible to users of the library. This will make it possible to
keep external systems in sync, but does not impose any particular
notification pattern.

The Row.from_json() call is added to be able to convert the 'old'
JSON response on an update to a Row object to make it easy for
users of notify() to see what changed, though this usage of Row
is quite different than Idl's typical use.

Signed-off-by: Terry Wilson <twilson at redhat.com>
---
 python/ovs/db/idl.py | 42 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 41 insertions(+), 1 deletion(-)

diff --git a/python/ovs/db/idl.py b/python/ovs/db/idl.py
index a01701a..45a5a23 100644
--- a/python/ovs/db/idl.py
+++ b/python/ovs/db/idl.py
@@ -26,8 +26,12 @@ vlog = ovs.vlog.Vlog("idl")
 
 __pychecker__ = 'no-classattr no-objattrs'
 
+ROW_CREATE = "create"
+ROW_UPDATE = "update"
+ROW_DELETE = "delete"
 
-class Idl:
+
+class Idl(object):
     """Open vSwitch Database Interface Definition Language (OVSDB IDL).
 
     The OVSDB IDL maintains an in-memory replica of a database.  It issues RPC
@@ -264,6 +268,17 @@ class Idl:
             self.lock_name = lock_name
             self.__send_lock_request()
 
+    def notify(self, event, row, updates=None):
+        """Hook for implementing create/update/delete notifications
+
+        :param event:   The event that was triggered
+        :type event:    ROW_CREATE, ROW_UPDATE, or ROW_DELETE
+        :param row:     The row as it is after the operation has occured
+        :type row:      Row
+        :param updates: For updates, a Row object with just the changed columns
+        :type updates:  Row
+        """
+
     def __clear(self):
         changed = False
 
@@ -386,6 +401,7 @@ class Idl:
             if row:
                 del table.rows[uuid]
                 changed = True
+                self.notify(ROW_DELETE, row)
             else:
                 # XXX rate-limit
                 vlog.warn("cannot delete missing row %s from table %s"
@@ -401,15 +417,19 @@ class Idl:
                           % (uuid, table.name))
             if self.__row_update(table, row, new):
                 changed = True
+                self.notify(ROW_CREATE, row)
         else:
+            op = ROW_UPDATE
             if not row:
                 row = self.__create_row(table, uuid)
                 changed = True
+                op = ROW_CREATE
                 # XXX rate-limit
                 vlog.warn("cannot modify missing row %s in table %s"
                           % (uuid, table.name))
             if self.__row_update(table, row, new):
                 changed = True
+                self.notify(op, row, Row.from_json(self, table, uuid, old))
         return changed
 
     def __row_update(self, table, row, row_json):
@@ -570,6 +590,26 @@ class Row(object):
             return
         self._idl.txn._write(self, column, datum)
 
+    @classmethod
+    def from_json(cls, idl, table, uuid, row_json):
+        data = {}
+        for column_name, datum_json in row_json.iteritems():
+            column = table.columns.get(column_name)
+            if not column:
+                # XXX rate-limit
+                vlog.warn("unknown column %s in table %s"
+                          % (column_name, table.name))
+                continue
+            try:
+                datum = ovs.db.data.Datum.from_json(column.type, datum_json)
+            except error.Error, e:
+                # XXX rate-limit
+                vlog.warn("error parsing column %s in table %s: %s"
+                          % (column_name, table.name, e))
+                continue
+            data[column_name] = datum
+        return cls(idl, table, uuid, data)
+
     def verify(self, column_name):
         """Causes the original contents of column 'column_name' in this row to
         be verified as a prerequisite to completing the transaction.  That is,
-- 
1.9.3