title: Django Rest framework keeps returning error on nested relationship
body: <p>Staring at my code for quite a while and I keep running into the same error. Funny thing is that I made a similar set of serializers for another part of my model and those work fine.</p>
  
  <p>This is the error that I keep getting:</p>
  
  <blockquote>
    <p>AttributeError at /onderhoudapi/conditiedeel/.json Got AttributeError
    when attempting to get a value for field <code>gebreken</code> on serializer
    <code>ConditiedeelSerializer</code>. The serializer field might be named
    incorrectly and not match any attribute or key on the <code>Conditiedeel</code>
    instance. Original exception text was: 'Conditiedeel' object has no
    attribute 'gebreken'.</p>
  </blockquote>
  
  <p>serializers.py</p>
  
  <pre><code>class GebrekSerializer(serializers.ModelSerializer):
      class Meta:
          model = Gebrek
          fields = ('naam', 'get_type', 'get_omvang_waarde', 'get_intensiteit_waarde', 'get_ernst_waarde')
  
  
  class ConditiedeelSerializer(serializers.ModelSerializer):
      gebreken = GebrekSerializer(many=True, read_only=True)
  
      class Meta:
          model = Conditiedeel
          fields = ('deel', 'conditiescore', 'gebreken', )
  </code></pre>
  
  <p>models.py</p>
  
  <pre><code>class Conditiedeel(models.Model):
      deel = models.OneToOneField(Deel, null=True, blank=True)
      conditiegroep = models.ForeignKey(Conditiegroep)
      conditiescore = models.IntegerField(choices=CONDITIE_KEUZES)
  
      #some class methods here
  
  
  class Gebrek(models.Model):
      naam = models.CharField(max_length=80)
      omvang = models.IntegerField(choices=OMVANG_KEUZES)
      intensiteit = models.IntegerField(choices=INTENSITEIT_KEUZES)
      conditiedeel = models.ForeignKey(Conditiedeel)
      nengebrek = models.ForeignKey(Nengebrek)
  
      #class methods here
  </code></pre>
  
  <p>As you can see, the <code>Gebrek</code> class has a foreign relationship to the Conditiedeel class. That should mean I can use a nested relationship like <a href="http://www.django-rest-framework.org/api-guide/relations/" rel="noreferrer">here</a>. I think I followed the example closely, yet I cannot get it to work.</p>