class Foo(models.Model):
  name = models.CharField()
  bar = models.ForeignKey("Bar")

class Bar(models.Model):
  name = models.CharField()

class FooSerializer(serializers.ModelSerializer):
  class Meta:
    model = Foo
    fields = ("id", "name", "bar", )
  bar = serializers.SlugRelatedField(read_only=True, slug_field="name")