title: Codeigniter's `where` and `or_where`
body: <p>I'm trying to specify a query in my model</p>
  
  <pre><code>$this-&gt;db
          -&gt;select('*')
          -&gt;from('library')
          -&gt;where('library.rating &gt;=', $form['slider'])
          -&gt;where('library.votes &gt;=', '1000')
          -&gt;where('library.language !=', 'German')
          -&gt;where('library.available_until &gt;=', date("Y-m-d H:i:s"))
          -&gt;or_where('library.available_until =', "00-00-00 00:00:00")
          -&gt;where('library.release_year &gt;=', $year_start)
          -&gt;where('library.release_year &lt;=', $year_end)
          -&gt;join('rating_repo', 'library.id = rating_repo.id')
  </code></pre>
  
  <p>So, the trouble i'm having is with my <code>or_where</code>. I want the <code>or</code> to be restricted to only the <code>available_until</code> field. Currently, however, i'm getting results which have a language of German which isn't what i want. How do i restrict my <code>or_where</code> filter to the <code>available_until</code> field only?</p>