title: ActiveRecord query differs when using string or instance variable
body: <p>If you view the query, <code>@bot_client_id</code> is a string with the same value of <code>string</code>.  However, I get different results when using them as part of my query.</p>
  
  <p>Why?</p>
  
  <pre><code>[24] pry(#&lt;BotResponse&gt;):1&gt; string
  =&gt; "aiaas-1409611358153-user-0149"
  
  [25] pry(#&lt;BotResponse&gt;):1&gt; @bot_client_id
  =&gt; "aiaas-1409611358153-user-0149"
  
  [26] pry(#&lt;BotResponse&gt;):1&gt; Event.where.has{(status == 'active') &amp; (bot_client_id == @bot_client_id)}
  =&gt; []
  [27] pry(#&lt;BotResponse&gt;):1&gt; Event.where.has{(status == 'active') &amp; (bot_client_id == string)}
  =&gt; [#&lt;Event:0x0000000464d120
    id: 22,
    bot_client_id: "aiaas-1409611358153-user-0149",
    keyword: "gratitude",
    topic: nil,
    status: "active",
    channel: "telegram",
    created_date: 2017-05-09 15:56:51 UTC,
    tickle_expression: "daily",
    time_of_day: "7:00 am",
    next_occurrence: 2017-05-14 14:00:00 UTC,
    time_zone: "America/Los_Angeles",
    recurring: true&gt;,
   #&lt;Event:0x0000000464cfb8
    id: 23,
    bot_client_id: "aiaas-1409611358153-user-0149",
    keyword: "daily_check",
    topic: nil,
    status: "active",
    channel: "telegram",
    created_date: 2017-05-10 04:25:47 UTC,
    tickle_expression: "daily",
    time_of_day: "9:00 am",
    next_occurrence: 2017-05-14 16:00:00 UTC,
    time_zone: "America/Los_Angeles",
    recurring: false&gt;]
  </code></pre>