title: How to pass choice display name to model serialize in Django REST framework?
body: <p>My env is Django 2.0.3, DRF 3.8.2 and Python 3.6.4.</p>
  
  <p>I have a model in <code>serializers.py</code>:</p>
  
  <pre><code>class TransferCostSerializer(serializers.ModelSerializer):
  
      def to_representation(self, instance):
          field_view = super().to_representation(instance)
          if field_view['is_active']:
              return field_view
          return None
  
      class Meta:
          model = TransferCost
          fields = ('id', 'destination', 'total_cost', 'is_active',)
  </code></pre>
  
  <p>Where <code>destination</code> field is choice field of 3 elements:</p>
  
  <pre><code>DESTINATION = (
      ('none', _('I will drive by myself')),
      ('transfer_airport', _('Only from airport')),
      ('transfer_round_trip', _('Round trip')),
  )
  </code></pre>
  
  <p>This is my <code>models.py</code>:</p>
  
  <pre><code>class TransferCost(models.Model):
  
      destination = models.CharField(
          _('Transfer Destination'), choices=DESTINATION, max_length=55
      )
      total_cost = models.PositiveIntegerField(
          _('Total cost'), default=0
      )
      is_active = models.BooleanField(_('Transfer active?'), default=True)
  
      class Meta:
          verbose_name = _('Transfer')
          verbose_name_plural = _('Transfers')
  
      def __str__(self):
          return _('Transfer {}').format(self.destination)
  </code></pre>
  
  <p>..And I return JSON like this:</p>
  
  <pre><code>[
      {
          id: 1,
          destination: "transfer_airport",
          total_cost: 25,
          is_active: true
      },
      {
          id: 2,
          destination: "transfer_round_trip",
          total_cost: 45,
          is_active: true
      }
  ]
  </code></pre>
  
  <p>How to return <code>destination</code> field with his display name? For example:</p>
  
  <pre><code>[
      {
          id: 1,
          destination_display: "Only from airport",
          destination: "transfer_round_trip",
          total_cost: 25,
          is_active: true
      },
      {
          id: 2,
          destination_display: "Round trip",
          destination: "transfer_round_trip",
          total_cost: 45,
          is_active: true
      }
  ]
  </code></pre>
  
  <p>Would be great to have something like <code>get_FOO_display()</code> in <code>serializers.py</code>, but it's not working. I need this thing, because I render form dynamically via Vue.js (as <code>v-for</code> select list).</p>