http://www.pocketsoap.com/weblog/2008/09/1824.html

Is the example in the link going to work for custom objects too?

Yes

Hey Simon,

Thanks for help!

In this example, the case record is being inserted (not upserted) and Account is also created on the fly. Whereas in our case the custom object B's record already exist in salesforce and we are Upserting A's records and want to link B's records in the same Upsert call.

The way we want to implement is the linking of Custom object B can be done in Upsert call to A itself. Rather than having statements to create new B records and assign external IDs to its field; we would like to sepcify the external ID in Upsert call itself.

As of now we are doing Upsert like

Upsert(<A's external ID field>, <list of A's records>);

Now, if we can pass the B's external ID field value too in this call, the linking should be achieved (Lookup value on object A should be populated with B's record).

Please let me know if I am not making myself clearer.

Thanks!

In the example i posted the case is created (but it could equally well be updated, or upserted, it doesn't matter), and the account is not created, its just a reference to an existing account, based on that externalId field on account's value. as far as i can tell, this is what you're looking for.