Sorry for the confusion...
I don't want to have a "Connection" in a database unless the connection is between existing "Blocks".
Please correct my class definition for Block and Connection so, that it won't be even possible to create such connection.

From: [] On Behalf Of Petr Jakeš
Sent: Wednesday, January 07, 2009 9:51 AM
To: Zoran Bošnjak
Subject: Re: [SQLObject] table ralations

# create dumb connection
# it should not work, because there is no blocks!!!
Connection(src=150, dst=250)

Why do you think this should not work? AFIK above mentioned just insert one row (record) in your table Connection. Exactly as the SQL below describes.

INSERT INTO "connection" VALUES(1,150,250); COMMIT;