Creé una aplicación Django 1.10 con Rest-Framework , tengo problemas para crear un campo personalizado que produzca el rango de fechas de un campo de fechas en M2MField , explicaré mi problema con mi código.

 class FoodConsumption(models.Model): ''' An item consume by animal. ''' animal = models.ForeignKey( Animal, related_name='animal_food_consumptions', on_delete=models.CASCADE) food = models.ForeignKey( Food, related_name='food_consumptions', on_delete=models.CASCADE) date = models.DateField() class FoodConsumptionTransaction(models.Model): herd = models.ForeignKey( Herd, related_name="food_consumption_transactions", on_delete=models.CASCADE ) food_consumptions = models.ManyToManyField(FoodConsumption)

Y aquí está mi serializador para mostrar los datos de FoodConsumptionTransaction .

 class FoodConsumptionTransactionListSerializer(serializers.ModelSerializer): class Meta: model = FoodConsumptionTransaction fields = ['id', 'herd', 'food_consumptions']

Cree un par de FoodConsumption :

 from dateutil import parser fc1 = FoodConsumption.objects.create( animal=animal_obj_1, food=food_obj_1, date=parser.parse('2017-04-06').date() // min date ) fc2 = FoodConsumption.objects.create( animal=animal_obj_2, food=food_obj_2, date=parser.parse('2017-04-08').date() ) fc3 = FoodConsumption.objects.create( animal=animal_obj_3, food=food_obj_2, date=parser.parse('2017-04-10').date() // max date ) # add to the transaction fc_trans = FoodConsumptionTransaction.objects.create( herd=herd_obj_1 ) fc_trans .food_consumptions.add(fc1, fc2, fc3)

Ahora, cuando obtengo datos de FoodTransaction por rebaño, obtengo esta lista:

 [ { "id": 1, "herd": 1, "food_consumptions": [1, 2, 3], # pks of FoodComsumption } ]

Pero, ¿cómo puedo crear campos adicionales basados en el campo food_consumptions , food.date (min y max) ?

 [ { "id": 1, "herd": 1, "food_consumptions": [1, 2, 3], # pks of FoodComsumption "min_date": '2017-04-6', # get the min date of food "max_date": '2017-04-10', # get the max date of food } ]