Question

我希望能够将我的borrower模型中的Asset字段（外键）设置为NULL，但似乎无法正常工作。我正在尝试发送包含密钥borrower等于NULL值的JSON数据的PATCH请求，但是borrower字段不会更新为NULL模型实例。也许序列化程序存在问题，导致无法将外键字段设置为NULL？

我已经尝试过将allow_null=True传递给BorrowSerializer类，但是没有用。我已经在StackOverflow的高处和低处搜索了具有类似问题和解决方案的帖子，但我尝试过的任何方法都没有效果。

这是我的模型。py：

from django.conf import settings
from django.db import models
from django.utils import timezone
from datetime import date
from django.contrib.auth.models import User
from django.urls import reverse

import uuid

class Category(models.Model):
    """Model representing an Asset category"""

    name = models.CharField(max_length=128)

    def __str__(self):
        return self.name

class Borrower(models.Model):
    first_name = models.CharField(max_length=64)
    last_name = models.CharField(max_length=128)
    associated_user = models.ForeignKey(User, on_delete=models.CASCADE, null=True)

    def __str__(self):
        return f'{self.first_name} {self.last_name}'

class Asset(models.Model):
    """Model representing an Asset"""
    # Unique identifier for an instance of an asset (a barcode of sorts)
    uid = models.UUIDField(primary_key=True, default=uuid.uuid4)
    name = models.CharField(max_length=200)
    manufacturer = models.CharField(max_length=64)
    model = models.CharField(max_length=128)
    description = models.TextField()
    category = models.ManyToManyField(Category)
    owner = models.ForeignKey(User, on_delete=models.CASCADE)
    borrower = models.ForeignKey(Borrower, on_delete=models.CASCADE, null=True, blank=True)
    checked_out = models.BooleanField(default=False)
    return_date = models.DateField(null=True, blank=True)    

    CONDITION_TYPE = (
        ('e', 'Excellent'),
        ('g', 'Good'),
        ('f', 'Fair'),
        ('p', 'Poor'),
    )

    condition = models.CharField(
        max_length=1,
        choices=CONDITION_TYPE,
        blank=True,
        help_text='Asset condition')

    class Meta:
            ordering = ['return_date']

    @property
    def is_dueback(self):
        if self.return_date and date.today() > self.return_date:
            return True
        return False

    def display_category(self):
        """Create a string for the Category. This is required to display category in Admin."""
        return ', '.join(category.name for category in self.category.all())

    display_category.short_description = 'Category'

    def __str__(self):
        return f'{self.uid} - {self.name}'

    def get_absolute_url(self):
        return reverse('asset-detail', args=[str(self.uid)])

这是我的serializers.py文件：

from rest_framework import serializers
from inventory.models import Asset, Borrower, Category

class BorrowerSerializer(serializers.ModelSerializer):
    class Meta:
        model = Borrower
        fields = ('first_name',
                  'last_name',
                  'associated_user'
        )

    def update(self, instance, validated_data):
        print('Update method triggered.')
        instance.first_name = validated_data.get('first_name', instance.first_name)
        instance.last_name = validated_data.get('last_name', instance.last_name)
        instance.associated_user = validated_data.get('associated_user'. instance.associated_user)
        instance.save()
        return instance

class CategorySerializer(serializers.ModelSerializer):
    class Meta:
        model = Category
        fields = '__all__'

class AssetSerializer(serializers.ModelSerializer):
    borrower = BorrowerSerializer(allow_null=True)
    category = serializers.StringRelatedField(many=True)
    condition = serializers.CharField(source='get_condition_display')

    class Meta:
        model = Asset
        fields = ('name', 
                  'manufacturer', 
                  'model',
                  'description',
                  'condition',
                  'category',
                  'borrower',
                  'checked_out',
                  'return_date',
                  'is_dueback',
        )

这是我的DRF API视图：

class AssetRetrieveUpdateDestroy(RetrieveUpdateDestroyAPIView):
    lookup_field = 'uid'
    serializer_class = AssetSerializer

    def get_queryset(self):
        user = self.request.user
        return Asset.objects.filter(owner=user)

class BorrowerRetrieveUpdateDestroy(RetrieveUpdateDestroyAPIView):
    lookup_field = 'id'
    serializer_class = BorrowerSerializer

    def get_queryset(self):
        return Borrower.objects.all()

当我传递此JSON时，我希望borrower模型实例中的Asset字段将更新为NULL：

data = {
   'borrower': null
}

但是，我的模型实例作为外键时不会更新borrower字段。如果该字段是CharField或其他名称，但在外键上，则可以正常工作。我打印了从我的AJAX请求返回的数据，但是borrower字段保持不变。

在此先感谢您提供的帮助。

Answer 1

来自the docs：

如果您支持可写的嵌套表示形式，则需要编写.create()或.update()方法来处理保存多个对象。

因此，您需要在.update()中实现AssetSerializer方法：

class AssetSerializer(serializers.ModelSerializer):
    borrower = BorrowerSerializer(allow_null=True)
    ...

    class Meta:
        model = Asset
        fields = (...)

    def update(self, instance, validated_data):
        instance.borrower = validated_data.get('borrower')
        instance.save()

        return instance

这应该可以完成工作。因此，无论您已传递allow_null=True，它都将接受空值，但是除非您定义自定义更新机制，否则它不会更新嵌套关系。

Django / Django Rest Framework-如何允许模型序列化程序将模型的外键字段设置为null？

1 个答案: