python - 模型中的 Django 循环导入
问题描述
我知道我在这里有一个循环导入,但是其中一个用于定义一些外键字段,另一个仅用于另一个模型中的属性。
楷模:
收据/models.py
from django.db import models
from employees.models import Employee
class Receipt(models.Model):
Supervisor = models.ForeignKey(Employee, on_delete=models.CASCADE, related_name='receipt_supervisor')
Employee = models.ForeignKey(Employee, on_delete=models.CASCADE, related_name='receipt_employee')
amount = models.DecimalField(max_digits=6, decimal_places=2)
员工/models.py
from django.db import models
from receipts.models import Receipt
class Employee(models.Model):
number = models.CharField(max_length=50, unique=True)
first_name = models.CharField(max_length=255)
last_name = models.CharField(max_length=255)
@property
def receipt_sum(self):
receipts = Receipt.objects.filter(Employee=self.pk)
sum = 0
for receipt in receipts:
sum += receipt.amount
return sum
我收到此错误:
无法从部分初始化的模块“employees.models”导入名称“员工”(很可能是由于循环导入)
有没有办法解决这个问题,以便我可以在 Employee 属性中进行收据查询?还是我需要在其他地方进行此计算?
谢谢!
解决方案
有没有办法解决这个问题,以便我可以在
Employee
物业中进行收据查询?
是的,您可以在方法中导入模块:
from django.db import models
class Employee(models.Model):
number = models.CharField(max_length=50, unique=True)
first_name = models.CharField(max_length=255)
last_name = models.CharField(max_length=255)
@property
def receipt_sum(self):
from receipts.models import Receipt
receipts = Receipt.objects.filter(Employee=self.pk)
sum = 0
for receipt in receipts:
sum += receipt.amount
return sum
但实际上根本不需要导入Receipt
,可以利用receipt_employee
relation来访问相关Receipt
对象,也可以使用.aggregate(…)
[Django-doc]在数据库端对元素进行汇总,这样可能效率更高:
from django.db import models
from django.db.models import Sum
class Employee(models.Model):
number = models.CharField(max_length=50, unique=True)
first_name = models.CharField(max_length=255)
last_name = models.CharField(max_length=255)
@property
def receipt_sum(self):
return self.receipt_employee.aggregate(
total=Sum('amount')
)['total'] or 0