title: Use model information before migration
body: <p>I'm trying to write a serializer in DRF which uses another before for a choicelist. However when I try to migrate (initially) I get an error because the serializer is trying to query for a table before it's created:</p>
  
  <pre><code>from api.models.stock import Stock
  from rest_framework import serializers
  
  class ChartSerializer(serializers.Serializer):
  
      symbol = serializers.ChoiceField(
          choices=Stock.objects.values_list('symbol', flat=True))
  
      option = serializers.ChoiceField(
          choices=['sparkline', '1d', '1w', '1m', '6m', '1y', '2y'])
  </code></pre>
  
  <p>The error is:</p>
  
  <blockquote>
    <p>django.db.utils.ProgrammingError: relation "api_stock" does not exist
    LINE 1: SELECT "api_stock"."symbol" FROM "api_stock"</p>
  </blockquote>
  
  <p>How can I change this? Do I need to check if <code>Stock</code> has been created before maybe?</p>