Django外键模型未保存引用

在 Django 中使用外键关系时，如果遇到模型未保存引用的问题，通常是因为在创建或更新相关对象时，有关联对象未被正确保存或引用。这里提供一些常见的问题和解决方案来确保你的外键关系正确处理。

1、问题背景

在使用 Django 进行模型开发时，遇到一个问题，外键模型无法保存引用。具体来说，UserProfile 模型的外键引用 Customer 模型，在保存 UserProfile 模型时，引用关系丢失。

代码如下：

from django.db import models
from customers.models import Customer
from django.contrib.auth.models import User, Group
from django.contrib.sites.models import Site
from anfitrion.models import ModelBase
from django.db.models.signals import post_save

class UserProfile(ModelBase):
    user = models.OneToOneField(User)
    customer = models.ForeignKey(Customer)
    address = models.CharField(max_length = 255)
    phone_home = models.CharField(max_length = 16)
    phone_office = models.CharField(max_length = 16)
    expiration = models.DateTimeField(null=True, blank=True)
    picture = models.ImageField(upload_to='profiles/%Y/%m/%d')
    observations = models.TextField(null=True, blank=True)
    status = models.BooleanField()

    def __str__(self):
        return "%s's profile" % self.user  

def create_user_profile(sender, instance, created, **kwargs):
    if created:
        profile, created = UserProfile.objects.get_or_create(user=instance)  

post_save.connect(create_user_profile, sender=User)

class SiteProfile(ModelBase):
    site = models.OneToOneField(Site)

    def __str__(self):
        return "%s's profile" % self.user  

def create_site_profile(sender, instance, created, **kwargs):
    if created:
        profile, created = SiteProfile.objects.get_or_create(site=instance)  

post_save.connect(create_site_profile, sender=Site)

function running the saveing
def users_save (request):
    #try:
        if request.is_ajax() and request.POST:
            user_id = request.POST['user_id']
            s = get_current_site(request)
            u = User (
                      username = request.POST['username'],
                      first_name = request.POST['first_name'],
                      last_name = request.POST['last_name'],
                      email = request.POST['email']
                      )
            u.set_password(request.POST['password'])
            c = None
            if int( request.POST['customer_id'] ) > 0: 
                c = Customer.objects.get(id=request.POST['customer_id'])
            up = UserProfile(
                      customer = c,
                      address = request.POST['address'],
                      phone_home = request.POST['phone_home'],
                      phone_office = request.POST['phone_office']
                      )
            up.user = u
            u.save()
            if int( request.POST['group_id'] ) > 0:
                g = Group.objects.get( id = request.POST['group_id'] )
                g.user_set.add(u)
            return HttpResponse(1, mimetype='application/json')

2、解决方案

经过分析，发现问题出在保存模型的方式上。在代码中，先保存了用户模型 u，然后再将 u 设置为 UserProfile 模型的 user 属性，最后才保存 UserProfile 模型。这种方式会导致外键引用丢失，因为在保存 UserProfile 模型时，u 还没有被保存，因此引用关系无法建立。

正确的做法是先保存 UserProfile 模型，然后再保存用户模型 u。这样，外键引用就可以正常建立。

up = UserProfile(
                      customer = c,
                      address = request.POST['address'],
                      phone_home = request.POST['phone_home'],
                      phone_office = request.POST['phone_office']
                      )
up.save()
up.user = u
u.save()

修改后的代码如下：

from django.db import models
from customers.models import Customer
from django.contrib.auth.models import User, Group
from django.contrib.sites.models import Site
from anfitrion.models import ModelBase
from django.db.models.signals import post_save

class UserProfile(ModelBase):
    user = models.OneToOneField(User)
    customer = models.ForeignKey(Customer)
    address = models.CharField(max_length = 255)
    phone_home = models.CharField(max_length = 16)
    phone_office = models.CharField(max_length = 16)
    expiration = models.DateTimeField(null=True, blank=True)
    picture = models.ImageField(upload_to='profiles/%Y/%m/%d')
    observations = models.TextField(null=True, blank=True)
    status = models.BooleanField()

    def __str__(self):
        return "%s's profile" % self.user  

def create_user_profile(sender, instance, created, **kwargs):
    if created:
        profile, created = UserProfile.objects.get_or_create(user=instance)  

post_save.connect(create_user_profile, sender=User)

class SiteProfile(ModelBase):
    site = models.OneToOneField(Site)

    def __str__(self):
        return "%s's profile" % self.user  

def create_site_profile(sender, instance, created, **kwargs):
    if created:
        profile, created = SiteProfile.objects.get_or_create(site=instance)  

post_save.connect(create_site_profile, sender=Site)

function running the saveing
def users_save (request):
    #try:
        if request.is_ajax() and request.POST:
            user_id = request.POST['user_id']
            s = get_current_site(request)
            u = User (
                      username = request.POST['username'],
                      first_name = request.POST['first_name'],
                      last_name = request.POST['last_name'],
                      email = request.POST['email']
                      )
            u.set_password(request.POST['password'])
            c = None
            if int( request.POST['customer_id'] ) > 0: 
                c = Customer.objects.get(id=request.POST['customer_id'])
            up = UserProfile(
                      customer = c,
                      address = request.POST['address'],
                      phone_home = request.POST['phone_home'],
                      phone_office = request.POST['phone_office']
                      )
            up.save()
            up.user = u
            u.save()
            if int( request.POST['group_id'] ) > 0:
                g = Group.objects.get( id = request.POST['group_id'] )
                g.user_set.add(u)
            return HttpResponse(1, mimetype='application/json')

通过修改代码，成功解决了 Django 外键模型无法保存引用的问题。

通过注意这些常见问题和采取正确的操作步骤，可以确保 Django 中的外键关系被正确处理，避免数据一致性和完整性问题。