"Cannot delete some instances of model '%s' because they are " "referenced through a protected foreign key: '%s.%s'" % ( field.remote_field.model.__name__, sub_objs[0].__class__.__name__, field.name ), sub_objs ) def SET(value): """ SET(), 此时需要指定 set 的值, 括号里...
Django 的ForeignKey 是一种逻辑上的两个表的关联关系,可以指定是否使用数据库的 FOREIGN KEY 约束。 如: from django.db import models class Province(models.Model): name = models.CharField(max_length=16) def __unicode__(self): return self.name class City(models.Model): name = models.CharField(...
4. 多对多关系(ManyToManyField), 对应数据库概念中的中间表, 比如model A中有一个字段是 ManyToManyField 到 model B,则数据库中会默认生成一个中间表,这个中间表默认包含三个字段, 主键id, 另外两个字段是 A和B的主键 作为外键, 也可以指定一个model作为这个中间表, 也可以关联自己, 比如: friend = models...
If you change the value of the primary key on an existing object and then save it, a new object will be created alongside the old one. For example: from django.db import models class Fruit(models.Model): name = models.CharField(max_length=100, primary_key=True) >>> fruit = Fruit....
Model): person = models.ForeignKey(Person, on_delete=models.CASCADE) group = models.ForeignKey(Group, on_delete=models.CASCADE) date_joined = models.DateField() invite_reason = models.CharField(max_length=64) When you set up the intermediary model, you explicitly specify foreign keys to the...
案例. 该模型使用外键引用自己本身。 from django.db import models class Category(models.Model): ...
link=False, to_field=None, db_constraint=True, **kwargs 假设我们有： class Author(models.Model...
Gender = models.ForeignKey('Coding',on_delete=models.CASCADE) # 关联Coding表格 ForeignKey (othermodel,on_delete,**options) 有两个必选的参数 : 第一个参数:关联的表格(主表),在默认的情况下,外键储存的是主表的主键(Primary key)。上面的例子里,关联到 Coding 表格,默认情况下储存 Coding 表格的主键 ...
living = models.ForeignKey(City, related_name="citizen", on_delete=models.CASCADE) def __unicode__(self): return self.firstname +self.lastname 对select_related 的操作,主要针对以上model来进行说明: 常用 model.tb.objects.all().select_related('外键字段') ...
django.db.utils.IntegrityError: FOREIGN KEY constraint failed STATUS MODEL EDDIT Maybe problem is here. The problem is appeared after i added some code which you can see in comments. "This last error suggests that the Status with pk=1 already exists, but your previous error suggests the contr...