title: Troubleshooting "Related Field has invalid lookup: icontains"
body: <p>I have the following models in <code>models.py</code>:</p>
  <pre><code>class ListinoTraduttore(models.Model):
          traduttore = models.ForeignKey('Traduttore', related_name='Traduttore')
          linguaDa = models.ForeignKey(Lingua, related_name = &quot;linguaDa&quot;)
          linguaA = models.ForeignKey(Lingua, related_name = &quot;linguaA&quot;)
          prezzoParola = models.CharField(max_length=50, blank=True)
          prezzoRiga = models.CharField(max_length=50, blank=True)
          scontoCat = models.CharField(max_length=50, blank=True)
          scontoFuzzy = models.CharField(max_length=50, blank=True)
          scontoRipetizioni = models.CharField(max_length=50, blank=True)
          class Meta:
                  verbose_name_plural = &quot;Listini Traduttori&quot;
          def __unicode__(self):
                  return u&quot;%s Da %s A %s Parola=%s Riga=%s ScontoCAT=%s ScontoFuzzy=%s ScontoRipetizioni=%s&quot; % (self.traduttore, self.linguaDa, self.linguaA, self.prezzoParola, self.prezzoRiga, self.scontoCat, self.scontoFuzzy, self.scontoRipetizioni)
  
  
  class Traduttore(models.Model):
          nome = models.CharField(nomeString, max_length=50)
          cognome = models.CharField(cognomeString, max_length=50)
          nomeAzienda = models.CharField(nomeAziendaString, max_length=50, blank=True)
          codiceFiscale = models.CharField(codiceFiscaleString, max_length=50, blank=True)
          partitaIva = models.CharField(partitaIvaString, max_length=50, blank=True)
          indirizzo = models.CharField(indirizzoString, max_length=50, blank=True)
          telefono = models.CharField(telefonoString, max_length=50, blank=True)
          fax = models.CharField(faxString, max_length=50, blank=True)
          email = models.EmailField(max_length=50, blank=True)
          referente = models.CharField(referenteString, max_length=50, blank=True)
          valuta = models.ForeignKey(Valuta)
          metodoPagamento = models.ForeignKey(MetodoPagamento)
          datiBancari = models.CharField(datiBancariString, max_length=50, blank=True)
          programmiUtilizzati = models.ManyToManyField(Programma, blank=True)
          note = models.CharField(max_length=200, blank=True)
          listino = models.ManyToManyField(ListinoTraduttore, related_name='listino', blank=True)
          def __unicode__(self):
                  return u&quot;%s %s %s&quot; % (self.nome, self.cognome, self.nomeAzienda)
          class Meta:
                  verbose_name_plural = &quot;Traduttori&quot;
  </code></pre>
  <p>While in the <code>admin.py</code> I have the following:</p>
  <pre><code>class TraduttoreAdmin(admin.ModelAdmin):
          list_display = (&quot;nome&quot;, &quot;cognome&quot;, &quot;nomeAzienda&quot;)
          search_fields = [&quot;nome&quot;, &quot;cognome&quot;, &quot;nomeAzienda&quot;]
  
  class ListinoTraduttoreAdmin(admin.ModelAdmin):
          list_display = (&quot;traduttore&quot;, &quot;linguaDa&quot;, &quot;linguaA&quot;, &quot;prezzoParola&quot;, &quot;prezzoRiga&quot;, &quot;scontoCat&quot;, &quot;scontoFuzzy&quot;, &quot;scontoRipetizioni&quot;)
          search_fields = ['traduttore__nome&quot;, &quot;linguaDa&quot;, &quot;linguaA&quot;]
  </code></pre>
  <p>But when I try to make a search in the admin page in the <code>ListinoTraduttore</code> table I have the following error:</p>
  <pre><code>TypeError at /admin/itrad/listinotraduttore/
  Related Field has invalid lookup: icontains
  Request Method: GET
  Request URL:    http://127.0.0.1:8000/admin/itrad/listinotraduttore/?q=Fenicio
  Django Version: 1.4.1
  Exception Type: TypeError
  Exception Value:    
  Related Field has invalid lookup: icontains
  Exception Location: /Library/Python/2.7/site-packages/django/db/models/fields/related.py in get_prep_lookup, line 142
  Python Executable:  /usr/bin/python
  Python Version: 2.7.2
  Python Path:    
  ['/Users/nicolac/Documents/DjangoProjects/mysite',
   '/Library/Python/2.7/site-packages/pip-1.1-py2.7.egg',
   '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python27.zip',
   '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7',
   '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-darwin',
   '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-mac',
   '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-mac/lib-scriptpackages',
   '/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python',
   '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-tk',
   '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-old',
   '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-dynload',
   '/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/PyObjC',
   '/Library/Python/2.7/site-packages']
  </code></pre>