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Editorial Team
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Asked: 2026-05-30T20:16:01+00:00

I access cassandra from the ruby gem. I want to retrive data from cassandra

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I access cassandra from the ruby gem. I want to retrive data from cassandra db by specifying which columns I want to. whenever I run this

conn.get(:column_family, ‘key1’, [63,62])

I get the following error,

 TypeError: can't convert Array into String
    from /home/ubuntu/.rvm/gems/ruby-1.9.2-p180@spaghetti/gems/thrift-0.8.0/lib/thrift/transport/framed_transport.rb:84:in `write'
    from /home/ubuntu/.rvm/gems/ruby-1.9.2-p180@spaghetti/gems/thrift-0.8.0/lib/thrift/protocol/binary_protocol.rb:112:in `write_string'
    from /home/ubuntu/.rvm/gems/ruby-1.9.2-p180@spaghetti/gems/thrift-0.8.0/lib/thrift/client.rb:35:in `write'
    from /home/ubuntu/.rvm/gems/ruby-1.9.2-p180@spaghetti/gems/thrift-0.8.0/lib/thrift/client.rb:35:in `send_message'
    from /home/ubuntu/.rvm/gems/ruby-1.9.2-p180@spaghetti/bundler/gems/cassandra-7474449189f3/vendor/0.8/gen-rb/cassandra.rb:107:in `send_multiget_slice'
    from /home/ubuntu/.rvm/gems/ruby-1.9.2-p180@spaghetti/bundler/gems/cassandra-7474449189f3/vendor/0.8/gen-rb/cassandra.rb:102:in `multiget_slice'
    from /home/ubuntu/.rvm/gems/ruby-1.9.2-p180@spaghetti/bundler/gems/thrift_client-00893a3accc5/lib/thrift_client/abstract_thrift_client.rb:150:in `handled_proxy'
    from /home/ubuntu/.rvm/gems/ruby-1.9.2-p180@spaghetti/bundler/gems/thrift_client-00893a3accc5/lib/thrift_client/abstract_thrift_client.rb:60:in `multiget_slice'
    from /home/ubuntu/.rvm/gems/ruby-1.9.2-p180@spaghetti/bundler/gems/cassandra-7474449189f3/lib/cassandra/protocol.rb:64:in `_multiget'
    from /home/ubuntu/.rvm/gems/ruby-1.9.2-p180@spaghetti/bundler/gems/cassandra-7474449189f3/lib/cassandra/cassandra.rb:619:in `multi_get'
    from /home/ubuntu/.rvm/gems/ruby-1.9.2-p180@spaghetti/bundler/gems/cassandra-7474449189f3/lib/cassandra/cassandra.rb:592:in `get'
    from (irb):5:in `block in irb_binding'
    from /home/ubuntu/.rvm/gems/ruby-1.9.2-p180@spaghetti/gems/connection_pool-0.1.0/lib/connection_pool.rb:41:in `with'
    from (irb):4
    from /home/ubuntu/.rvm/rubies/ruby-1.9.2-p180/bin/irb:16:in `<main>'

A python package ‘pycassa’ provides the option to specify which columns to be retrieved. How to do that in ruby??

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1 Answer

  1. Editorial Team

    Currently .get() and .multi_get() do not accept a list of column names. There is an open issue for this on GitHub. As a work around you can use .get_columns() instead.

    conn.get_columns(:column_family, 'key1', [63,62])

    This returns an array of values in the same order as you specified for your column names. Alternatively you could use the cassandra-cql gem:

    handle.execute("select 63,62 from column_family where KEY = 'key1'").fetch
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