title: function ts_rank_cd(text, tsquery) does not exist
body: <p>I'm using full text search supported by postgres, I installed <code>acts_as_tsearch</code> plugin and it works successfully, but when I tried it later I found an error</p>
  
  <blockquote>
    <p>runtimeError: ERROR C42883 Mfunction ts_rank_cd(text, tsquery) does
    not exist HNo function matches the given name and argument types. You
    might need to add explicit type</p>
  </blockquote>