name = models.CharField(max_length=32) pub = models.ForeignKey(Publisher, on_delete=models.CASCADE, ) # def __str__(self): # return self.name """ on_delete 在2.0版本之后是必填的 on_delete= models.CASCADE 级联删除 PROTECT 保护 SET(1) SET_DEFAULT 设置为默认值设置为某一个值 SET_NULL ...
1.ForeignKey 初始化的参数有: to, on_delete, related_name=None, related_query_name=None,limit_choices_to=None, parent_link=False, to_field=None, db_constraint=True, **kwargs 假设我们有: classAuthor(models.Model): author= models.CharField(max_length=250)classBooks(models.Model): book= mod...
model_b = models.ForeignKey(ModelB, on_delete=models.CASCADE) ``` 上面的代码演示了如何在ModelB中创建一个manytomanyfield字段,与ModelA建立多对多关系。通过设置related_name参数为"models_b",我们已经定义了从ModelB到ModelA的反向访问方式。通过设置through参数为"IntermediateTable",我们还定义了使用Intermediate...
through='Membership',through_fields=('group','person'), )classMembership(models.Model):group = models.ForeignKey(Group, on_delete=models.CASCADE) person = models.ForeignKey(Person, on_delete=models.CASCADE) inviter = models.ForeignKey( Person, on_delete=models.CASCADE, related_name="membership_in...
ForeignKey.on_delete 当一个model对象的ForeignKey关联的对象被删除时,默认情况下此对象也会一起被级联删除的。 ? 1 user=models.ForeignKey(User, blank=True, null=True, on_delete=models.CASCADE) CASCADE:默认值,model对象会和ForeignKey关联对象一起被删除 ...
from django.db import models class Book(models.Model): name = models.CharField(max_length=100) authors = models.ManyToManyField(Author, through='BookAuthor', through_fields=('book', 'author')) class BookAuthor(models.Model): book = models.ForeignKey(Book, on_delete=models.CASCADE) author =...
Silent deletion could be prevented by settingon_delete=models.PROTECTon any relation to the explicit through-model, but then you would first have to be aware of the necessity. When using a "real" auto-createdthroughtable (i.e. an implicit one) the issue does not arise, because there is ...
(models.Model): title = models.CharField(max_length=100) authors = models.ManyToManyField(Author, through='BookAuthor') class BookAuthor(models.Model): book = models.ForeignKey(Book, on_delete=models.CASCADE) author = models.ForeignKey(Author, on_delete=models.SET_NULL, null=True) class Meta...
(TRIPLE,'Triple'),)pizza=models.ForeignKey('Pizza',related_name='topping_amounts',on_delete=models.SET_NULL,null=True)topping=models.ForeignKey('Topping',related_name='topping_amounts',on_delete=models.SET_NULL,null=True,blank=True)amount=models.IntegerField(choices=AMOUNT_CHOICES,default=...
User = get_user_model() class Follow(models.Model): user = models.ForeignKey( User, on_delete=models.CASCADE, related_name='followers' ) following = models.ForeignKey( User, on_delete=models.CASCADE, related_name='following' ) created = models.DateTimeField( 'Creation Time', auto_now_add=...