如何覆盖 django save 方法以动态更新某些字段？

Question

这里我有两个模型。在这些模型中，我想在Ledger 模型中使amount_to_pay 的值动态化。例如，这两个模型有两种不同的形式，如果用户选择payment_option 来自 ledger 模型并为 amount_to_pay 字段提供一些值，那么如果只有 ledger.id 和 expense.payment_option_id 相同，那么分类帐模型中 amount_to_pay 的值应替换为该值。如何我可以吗？

models.py

     class Expense(models.Model):
        pay_from = models.CharField(max_length=200)
        payment_option = models.ForeignKey('Ledger', on_delete=models.CASCADE)
        amount_to_pay = models.IntegerField(default=0)
        expense_date = models.DateField(default=datetime.date.today)
        expense_type = models.ForeignKey(ExpenseType, on_delete=models.CASCADE)
        note = models.TextField()
        created = models.DateTimeField(auto_now_add=True)
        updated = models.DateTimeField(auto_now=True)
        slug = AutoSlugField(unique_with='id', populate_from='expense_type')

        def get_amount_to_pay(self):
            return self.amount_to_pay


    class Ledger(models.Model):
        name = models.CharField(max_length=200)
        account_number = models.CharField(max_length=250, unique=True)
        account_type = models.CharField(max_length=200)
        opening_balance = models.IntegerField(default=0)
        amount_to_pay = models.IntegerField(default=0, blank=True, null=True)
        current_balance = models.IntegerField(default=0, blank=True, null=True)
        created = models.DateTimeField(auto_now_add=True)
        updated = models.DateTimeField(auto_now=True)
        slug = AutoSlugField(unique_with='id', populate_from='name')

        def save(self, *args, **kwargs):
             self.amount_to_pay = Expense.get_amount_to_pay(self)

# here how can i save the amount_to_pay from expense form if the ledger.id and expense.payment_option.id matches??
#i got stuck here.           
 self.current_balance = self.opening_balance - self.amount_to_pay

            super(Ledger, self).save(*args, **kwargs)

Answer 1

覆盖保存方法并在 django 中动态更新某些字段

对于我的情况，当我对答案发表评论时，我想动态更新答案模型中的完成列，它应该返回 true 而不是 False。因此，在我的示例中，我正在检查已完成的布尔列是否为 False，如果为 False，我使用 Comment 中的答案对象将其状态更改为 True，然后保存答案对象，请参阅有关更新与插入字段 @987654321 的更多信息@

class Answer(models.Model):
    user = models.ForeignKey("User", on_delete=models.CASCADE, blank=True, null=True)
    username = models.CharField(max_length=250)
    codeAnswer = models.CharField(max_length=250)
    girAnswer = models.CharField(max_length=250)
    correct = models.BooleanField(default=False)
    firebaseToken = models.CharField(max_length=250)
    done = models.BooleanField(default=False)
    created_at = models.DateTimeField()
    updated_at = models.DateTimeField(auto_now=True)

    def __unicode__(self):
        return "{0}: {1}".format(self.username, self.value)

    def __str__(self):
        return "%s" % (self.codeAnswer)

# So here i override the save method in the Comment model to do what i want as below.

class Comment(models.Model):
    answer = models.ForeignKey("Answer", on_delete=models.CASCADE, blank=False , related_name="comments")
    writerName = models.CharField(max_length=250)
    content = models.CharField(max_length=250)
    deleted = models.BooleanField(default=False)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)

    def __str__(self):
        return "%s" % (self.writerName)

    def save(self, *args, **kwargs):
        if self.answer.done is False:
            self.answer.done = True
            self.answer.save()
        super(Comment, self).save(*args, **kwargs)

希望它能回答上面的问题，谢谢

Answer 2

检查 Ledger 是否有孩子，然后更新它：

class Expense(models.Model):    
        def save(self, *args, **kwargs):
                self.payment_option.amount_to_pay = self.payment_option.amount_to_pay + self.amount_to_pay
                self.payment_option.save()
            super(Expense, self).save(*args, **kwargs)

Answer 3

解决方案一：

我认为与其更改Ledger 模型，不如更改Expense 模型，如下所示：

class Expense(models.Model):
    ...
    def save(self, *args, **kwargs):
       self.payment_option.amount_to_pay = self.payment_option.amount_to_pay + self.amount_to_pay
       self.payment_option.save()
       super(Expense, self).save(*args, **kwargs)

方案二：

但老实说，解决方案一对我来说似乎并不好。原因是您将相同的数据保存在 2 个地方（费用和分类帐中）。相反，它应该是一次，然后应该动态计算Ledger 中的amount_to_pay 值。像这样：

from django.db.models import Sum

class Ledger(...):

     @property
     def amount_to_pay(self):
         # I am using a property method to show the amount_to_pay value.
         # FYI: in this way, you need to remove amount_to_pay field from Ledger model
         return self.opening_balance - self.expense_set.all().aggregate(a_sum=Sum('amount_to_pay')).get('a_sum', 0)

这样，对于每个分类帐，amount_to_pay 的值将在运行时动态计算。例如：

 for l in Ledger.objects.all():
     l.amount_to_pay

解决方案三：

如果您对使用先前解决方案中的每个l.amount_to_pay（因为它从 DB 动态计算 amount_to_pay）产生 DB 命中持谨慎态度，那么您始终可以使用 annotate 值。像这样：

对于此解决方案，您需要更改 Expense 模型并添加 related_name：

class Expense(models.Model):
    pay_from = models.CharField(max_length=200)
    payment_option = models.ForeignKey('Ledger', on_delete=models.CASCADE, related_name='expenses')

然后像这样在查询中使用related_name（仅供参考：对于以下使用示例，您不能在 Ledger 模型中保留 def amount_to_pay(...) 方法）：

from django.db.models import Sum, F, ExpressionWrapper, IntegerField

ledgers = Ledger.objects.all().annotate(expense_sum=Sum('expenses__amount_to_pay')).annotate(amount_to_pay=ExpressionWrapper(F('opening_balance') - F('expense_sum'), output_field=IntegerField()))

# usage one
for l in ledgers:
   l.amount_to_pay

# usage two
ledgers.values('amount_to_pay')

Answer 4

最好的办法是你用任何你有foreginkey的方式覆盖save方法中的调用。

    def save(self, *args, **kwargs):
        #self.date_created = timezone.now()
        # YOUR LOGIC HERE
        super(YOUR_OVERRIDING_MODEL , self).save(*args, **kwargs