title: How can I make tastypie filter on a foreign field?
body: <p>I have two models like this:</p>
  
  <pre><code>class CompanyResource(ModelResource):
      class Meta:
          queryset = Company.objects.all()
          fields = ['title', 'latitude', 'longitude']
          resource_name = 'company'
          filtering = {
              'latitude': ALL,
              'longitude': ALL
          }
  
  class EventResource(ModelResource):
      company = fields.ToOneField(CompanyResource, 'company', full=True)
      class Meta:
          fields = ['title', 'company']
          queryset = Event.objects.all()
          resource_name = 'event'
          filtering = {
              'company': ALL_WITH_RELATIONS
          }
  </code></pre>
  
  <p>Then I try to access <code>/api/v1/event/?format=json&amp;company_latitude__within=2,3</code> or <code>/api/v1/event/?format=json&amp;company_latitude__lt=1</code> it isn't filtered on latitude:</p>
  
  <pre><code>{
      "meta": {
          "limit": 20, 
          "next": "/api/v1/event/?offset=20&amp;limit=20&amp;format=json", 
          "offset": 0, 
          "previous": null, 
          "total_count": 329
      }, 
      "objects": [
          {
              "company": {
                  "latitude": "1.30521100000000", 
                  "longitude": "103.81116299999996", 
                  "resource_uri": ""
              }, 
              "resource_uri": "/api/v1/event/16/", 
              "title": "50% off at Infusion@Dempsey, $50 for $100 worth of Fine Dining"
          }
      ]
  }
  </code></pre>
  
  <p>How can I make this work?</p>