django - how - Agregar campos personalizados en un serializador basado en criterios de instancia

django rest framework serializer

Question

Django 1.10 una aplicación Django 1.10 con Rest-Framework , tengo problemas para crear cualquier campo personalizado que M2MField el rango de fechas de un campo de fecha 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'']

Crea 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 FoodTransaction datos de FoodTransaction por manada, obtengo esta lista:

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

Pero, ¿cómo puedo crear campos adicionales basados ​​en los campos de food_consumptions de 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
    }
]

Answer 1

Lo que quieres son serializadores .

Puede anular el resultado predeterminado devuelto por la función to_representation() del serializador. Y agregue los campos min_date y max_date al resultado producido.

Como

class  FoodSerializer(serialiers.ModelSerializer):
    def to_representation(self, instance):
        result = super(FoodSerializer, self).to_representation(instance)     
        result[''min_date''] = min[each.date for each in instance.m2mfield.all()]
        result[''max_date''] = max[each.date for each in instance.m2mfield.all()] 
        return result