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.
create dumb connection
# it should not work, because there is no
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
INTO "connection" VALUES(1,150,250); COMMIT;