Question

错误消息：

blogs.Permission: (fields.E336) The model is used as an intermediate model by 'blogs.Category.permission', but it does not have a foreign key to 'Category' or 'Permission'.

我试图在“权限”模型下向“类别”添加外键，仍然会发生相同的错误。

models.py：

from django.db import models

class Category(models.Model):
    name = models.CharField(max_length=50)
    permission = models.ManyToManyField('Permission',
                                        related_name='category_permissions',
                                        through='Permission'
                                        )

    def __str__(self):
        return self.name


class Permission(models.Model):
    HIGH = 'High'
    MEDIUM = 'Medium'
    LOW = 'Low'
    CLASSIFICATION_CHOICES = [
        (HIGH, 'High'),
        (MEDIUM, 'Medium'),
        (LOW, 'Low')
    ]
    category_name = models.ForeignKey(Category, on_delete=models.CASCADE, related_name='category_name')
    name = models.CharField(max_length=100)
    description = models.TextField()
    platform = models.CharField(
        max_length=10,
        choices=PLATFORM_CHOICES,
        default=BOTH,
    )
    classification = models.CharField(
        max_length=10,
        choices=CLASSIFICATION_CHOICES,
        default=LOW,
    )

    def __str__(self):
        return self.name


class MobileApp(models.Model):
    name = models.CharField(max_length=200)
    icon = models.ImageField(upload_to='app_icons', blank=True, null=True)
    platform = models.CharField(
        max_length=10,
        choices=PLATFORM_CHOICES,
        default=IOS,
    )
    category = models.ManyToManyField('Category')
    provider = models.CharField(max_length=200)
    identifier = models.CharField(max_length=200)
    permission = models.ManyToManyField(Permission,
                                        related_name='mobile_app_permission',
                                        )

    def __str__(self):
        return self.name

我正在尝试使用'through'参数来包括对MobileApp和Category的权限m2m的描述字段

Answer 1

这很糟糕。

显然，您希望多对多介于Category和MobileApp之间，直通模型为Permission。因此，m2m字段需要声明：

val size = someOtherObject.subObjects().size
val s = size match {
  case size > 0 => "Size is greater than 0"
  case _ => "Size is less than 0"
}

第二，作为错误状态，在直通模型中，您都需要双方的外键。另外，您需要给他们提供明智的名称和related_names。所以：

class Category(models.Model):
    name = models.CharField(max_length=50)
    permission = models.ManyToManyField('MobileApp',
                                        related_name='category_permissions',
                                        through='Permission'
                                        )

最后，您不需要还需要在另一个方向上将m2ms定义为权限或类别。从MobileApp中删除class Permission(models.Model): category = models.ForeignKey(Category, on_delete=models.CASCADE, related_name='permissions') mobile_app = models.ForeignKey('MobileApp', on_delete=models.CASCADE, related_name='permissions')和category字段。

如何解决“该模型与中间模型一样使用，但没有模型的外键”？

1 个答案: