django - 在django模型保存方法中获取ManytoMany字段的选定值

Question

我正在尝试从 Django admin 将数据添加到表BillRecord。我需要访问模型save中ManytoMany字段的选定值方法并需要根据 ManytoMany 字段的选定对象执行一些逻辑。

class ProductType(BaseApplicationModel):
   name = models.CharField(max_length=128)

class Product(BaseApplicationModel)
   type = models.ForeignKey(ProductType,related_name="products")

class BillRecord(BaseApplicationModel):
    products = models.ManyToManyField(Product, related_name="billrecords")

    def save(self, *args, **kwargs):
       super(BillRecord, self).save(*args, **kwargs)
       for product in self.products.all():
          print product

在代码中，当我尝试打印产品的值时，它给我 billing.Product.None 即 self.products.all() 返回空查询集

我需要获取 ManyToMany 字段选择框中所选对象的 ID。

Answer 1

问题在于，当 Product 与您的 BillRecord 实例关联时，它并不总是保存。对于多对多关系，您可以先保存任一对象。正确的处理方法是使用 m2m-changed signal :

Sent when a ManyToManyField is changed on a model instance. Strictly speaking, this is not a model signal since it is sent by the ManyToManyField, but since it complements the pre_save/post_save and pre_delete/post_delete when it comes to tracking changes to models, it is included here.

所以你应该尝试如下操作:

from django.db.models.signals import m2m_changed

...your models here...

def products_changed(sender, **kwargs):
    # Do something here
    pass

m2m_changed.connect(products_changed, sender=BillRecord.products.through)