title: Django filtering a model query with filter method
body: <p>Why does this code:</p>
  <pre><code>products_model = Product.objects.filter(sub_category__name__iexact=sub)
  supplier_filter = SupplierFilter(request.GET, queryset=products_model)
  products = supplier_filter.qs
  </code></pre>
  <p>Give me this error:</p>
  <pre><code>Field 'id' expected a number but got 'BYGGMAX'.
  </code></pre>
  <p>Ive had trouble with this alot now. Can someone explain whats goin on. When i use the filter method its more complicated to filter the model, how so? Really interested in learning more on how this works.</p>