[Fwd: RE: implementing a large table over a database]

[Martin Janzen]

Dave Barratt wrote:
> Thanks for your excellent posting on dynamic tables, its saving me alot of
> headaches.

Glad to hear it!

> As a newbie to Agent development I was wondering if you could
> expand on what the following methods you reference in your examples below
> would actually do...
> 
> bool MyDatabaseTable::loadRow(const Oidx& indexOid)
 > {
       // This extracts the database key from the index OID, and updates
       // the columns of the corresponding row in the MIB table.  If your
       // MIB design corresponds fairly closely to your database schema,
       // this ought to be easy:

       // Make sure the caller has handled all the special cases.
       assert(indexOID.len() == 1);  // (adjust for number of keys)

       // Extract key(s) from the index OID.
       int key1 = indexOID[0];
       if ( /* key1 is invalid */ ) return false;

       return fillRow(key1);
 > }



> bool MyDatabaseTable::fillRow(int slot)
 > {
       // Look up the necessary data in the database.  In this case,
       // 'slot' is the database key.
       [...]

       // Create a new row, then fill it in.
       Agentpp::Oidx indexOID;
       indexOID += slot;    // set the row index
       Agentpp::MibTableRow* pRow = mTable.add_row(indexOID);
       mTable.set_row(pRow, /* data values for columns... */);
       return true;
 > }

The set_row() method is generated by AgentPro, but if you're not using 
that, typically you just need something like this to fill the columns:

   void tspTransportStreamEntry::set_row(
       MibTableRow* r, unsigned long p0, long p1, [...])
   {
       r->get_nth(0)->replace_value(new Gauge32(p0));
       r->get_nth(1)->replace_value(new SnmpInt32(p1));
       [...]
   }


> bool MyDatabaseTable::checkSlotIndex(int slot, Oidx indexOid, int i)

Just an implementation detail.  I have lots of objects keyed by 'slot', 
so this does the key extraction and validity check described above. 
Should have deleted it from the example.

HTH...


-- 
Martin Janzen
janzen at pixelmetrix dot com