title: ModelSerializer using model property
body: <p>I'm trying to serialize a model containing a property field that I also want to serialize. </p>
  
  <p>models.py:</p>
  
  <pre><code>class MyModel(models.Model):
      name = models.CharField(max_length=100)
      slug = models.AutoSlugField(populate_from='name')
  
      @property
      def ext_link(self):
          return "/".join([settings.EXT_BASE_URL, self.slug])
  </code></pre>
  
  <p>serializers.py:</p>
  
  <pre><code>class MyModelSerializer(serializers.ModelSerializer):
      class Meta:
          model = MyModel
          fields = ('name', 'ext_link')
  </code></pre>
  
  <p>When trying to get to the related URL, I'm getting a serializer exception (KeyError) on the <code>ext_link</code> property. </p>
  
  <p>How can I serialize the <code>ext_link</code> property?</p>