title: Rails find or create based on two fields
body: <p>I have a venue model and i want to do this</p>
  
  <pre><code>Venue.find_or_create_by_
  </code></pre>
  
  <p>but i only want a new venue to be created if one with the same name and date do not already exist</p>
  
  <p>For example</p>
  
  <pre><code>=&gt; Venue(id: integer, location: string, showdate: datetime, created_at: datetime, updated_at: datetime)
  </code></pre>
  
  <p>A venue is unique and needs to be created if the location and the showdate are not present in the db</p>