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Date: Mon, 24 Jun 2013 20:23:57 -0700
From: Blair Zajac <blair@orcaware.com>
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To: "user@cassandra.apache.org" <user@cassandra.apache.org>
Subject: How to do a CAS UPDATE on single column CF?
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How does one do an atomic update in a column family with a single column?

I have a this CF

   CREATE TABLE schema_migrations (
     version TEXT PRIMARY KEY,
   ) WITH COMPACTION = {'class': 'LeveledCompactionStrategy'};

that records which database migrations have been applied.  I want to do 
a CAS UPDATE to add a dummy lock token to prevent multiple migrations 
from running, but these three attempts fail (using the Python cql client):


 >>> cursor.execute("UPDATE schema_migrations SET version = 'locked' 
WHERE version = 'locked' IF NOT EXISTS")
cql.apivalues.ProgrammingError: Bad Request: PRIMARY KEY part version 
found in SET part


 >>> cursor.execute("UPDATE schema_migrations SET WHERE version = 
'locked' IF NOT EXISTS")
cql.apivalues.ProgrammingError: Bad Request: line 1:29 no viable 
alternative at input 'WHERE'


 >>> cursor.execute("INSERT INTO schema_migrations (version) VALUES 
('locked') IF NOT EXISTS")
cql.apivalues.ProgrammingError: Bad Request: line 1:58 missing EOF at 'IF'

Thanks,
Blair