根据实例条件在串行器中添加自定义字段 [英] Add custom fields in a serializer based from instance criteria

问题描述

我创建了一个 Django 1.10 应用程序与 Rest-Framework ，我有麻烦制作任何自定义字段将产生日期字段的日期范围在 M2MField 中，我将用我的代码解释我的问题。

 FoodConsumption（models.Model）：
'''
动物消耗的物品。 
'''
 
 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）
  

这里是我的序列化程序显示 FoodConsumptionTransaction 数据。

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

创建两个 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（
动物= animal_obj_3，
 food = food_obj_2，
 date = parser.parse（'2017-04-10'）。date（）//最大日期
）
 
 ＃add to the transaction 
 
 fc_trans = FoodConsumptionTransaction.objects.create（
 herd = herd_obj_1 
）
 fc_trans .food_consumptions.add（fc1，fc2，fc3）
  

现在，通过herd我们获取 FoodTransaction 的数据获得此列表：

  [
 {
id：1，
 herd：1，
food_consumptions：[1，2，3]，FoodComsumption的$ p 
} 
] 
   food_consumptions 字段创建额外的字段，$ code> food.date  （最小和最大）？
  [
 {
id：1，
herd：1，
food_consumptions：[1，2，3]，FoodComsumption的$ p 
min_date：' 04-6'，＃获取食物的最小日期
max_date：'2017-04-10'，＃获取食物的最大日期
} 
] 
  
 
 
解决方案
你想要的是序列化程序。
 
 
 
您可以覆盖从串行器的 to_representation（）函数。并为生成的结果添加 min_date 和 max_date 字段。
 
 
 
如
  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 example.m2mfield.all（）] 
 return result 
  
 
I created a Django 1.10 app with Rest-Framework, I have trouble making any custom field that will yield the date range of a date field in M2MField, i will explain my problem with my code.
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)
And here is my serializer to display the FoodConsumptionTransaction data.
class FoodConsumptionTransactionListSerializer(serializers.ModelSerializer):

    class Meta:
        model = FoodConsumptionTransaction
        fields = ['id', 'herd', 'food_consumptions']
Create a couple of 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)
Now when getting data of FoodTransaction by herd i get this list:
[
   {
       "id": 1,
       "herd": 1,
       "food_consumptions": [1, 2, 3], # pks of FoodComsumption
   }
]
But how can i create extra fields based from food_consumptions field , food.date (min and 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
    }
]

解决方案
What you want are serializers.

You can override the default result returned from the serializer's to_representation() function. And add min_date and max_date fields to the result produced.

Such as
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


                        
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