title: Django queryset filter after a concatenation of two columns
body: <p>Is there any way to filter a model using a concatenation of two of its columns? My model is like this:</p>
  
  <pre><code>class Item(models.Model):
      series = models.CharField(max_length=50)
      number = models.CharField(max_length=50)
  </code></pre>
  
  <p>What I need is to filter after the concatenation of the two columns, if a user inputs A123 I want to be able to find any Item that has series and number like %A and 123% or %A1 and 23%
  Is this possible using the django models? Or is it possible with raw sql?
  I would rather not construct a new column with the concatenation.</p>