Question

这里我有两个模型。在这些模型中，我想使Ledger模型中的amount_to_pay值动态化。例如，对于这两个模型，我有两种不同的形式，并且如果用户选择来自分类账模型并为amount_to_pay字段提供一些值，如果仅ledger.id和expense.payment_option_id相同，则应替换分类账模型中的amount_to_pay值。我该怎么做？

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

解决方案一：

我认为您应该在Ledger模型中进行更改，而不是在Expense模型中进行更改，像这样：

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)

解决方案二：

但是，老实说，解决方案对我来说并不好。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，然后应动态计算amount_to_pay中的Ledger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，值amount_to_pay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：

如果您不愿使用先前解决方案中的每个l.amount_to_pay（因为它是从DB动态计算出amount_to_pay）来命中数据库的，那么您始终可以annotate来使用该值。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：您无法在 Ledger 模型中保留 def amount_to_pay(...) 方法用于以下用途示例）：

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 2

最好的是，您可以使用前键来以任何方式覆盖save方法中的调用。

set Path="D:\hello\abc\old"
for /f "tokens=*" %%a in ('dir /A:-D /B /O:-D /S %Path%') do set NEW=%%a&& goto:n 
:n
echo %NEW%

Answer 3

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)

如何重写django保存方法以更新某些字段？

3 个答案:

解决方案一：

解决方案二：

解决方案三：