lookup_field = 'username'


class SpeakerSerializer(serializers.HyperlinkedModelSerializer):
    user = serializers.HyperlinkedRelatedField(view_name='user-detail',
        read_only=True, lookup_field='username')


class Meta:
    model = Speaker
fields = 'url', 'user'
lookup_field = 'user__username'
django rest framework lookup_field через OneToOneField