SET_NULL:将model对象的ForeignKey字段设为null。当然需要将null设为True。 SET_DEFAULT:将model对象的ForeignKey字段设为默认值。 Protect:删除ForeignKey关联对象时会生成一个ProtectedError,这样ForeignKey关联对象就不会被删除了。 SET():将model对象的ForeignKey字段设为传递给SET()的值。 1 2 3 4 5 defget_sentin...
表示foreign_key 默认的属性名称。 我们可以通过related_name指定它的名称。例如, Gender = models.ForeignKey('Coding',related_name='list_xingbie') 当多个foreignkey指向同一个主表,related_name必须设置。 指定了foreignkey属性名称的为xingbie,查询语句对比: $ c.list_set.all() % 默认属性 $ c.list_xingb...
如果在 rule 中查询 rule.allowed,Django 会自动锁定外键对应的表为robots_rule_allowed 通过查询这个表得到对应的 url_id(多个),然后去 robots_url 表中提取相应记录。 2、ForeignKey 1 2 3 4 5 6 7 8 9 10 11 12 classThreadedComment(models.Model): ... # Generic Foreign Key Fields content_type=m...
Foreign_Key字段在哪张表就可以哪张表使用 Foreign_Key字段连表,反之没有Foreign_Key 字段就使用与其关联的 小写表名; 1对多:对象.外键.关联表字段,values(外键字段__关联表字段) 多对多:外键字段.all() ② 反向连表操作 通过value、value_list、fifter 方式反向跨表:小写表名__关联表字段 通过对象的形式反...
foreign key: 表与表之间的某种约束关系,由于这种关系的存在能够让表与表之间的数据更加完整,关联性更强; 1.1 在创建表时就对表的某些字段(与另一张表的主键相关联的字段)进行外键约束设置; table person2( id int not null auto_increment primary key, ...
If there are more than two foreign keys though, you must also specify through_fields as above, or a validation error will be raised. Now that you have set up your ManyToManyField to use your intermediary model (Membership, in this case), you’re ready to start creating some many-to-many...
Django model update foreign key 外键更新 migrate操作1,parent model :执行makemigratios,migrate2,child model :foreign key 注释掉,执行makemigratios,migrate(删掉外键...)3,child model :foreign key 注释解除,执行makemigratios,migrate(追加外键)詳細:parent変更前:python manage makemigrations...python manage...
If there are more than two foreign keys though, you must also specify through_fields as above, or a validation error will be raised. Now that you have set up your ManyToManyField to use your intermediary model (Membership, in this case), you’re ready to start creating some many-to-many...
When is_valid methods of ListSerializer, the queryset of the PrimaryRelatedKeyField of the Serializer specified as child is executed for the number of elements in the List. The queryset is evaluated as many times as the number of elements in the List. Is there any way to avoid this? I ...
If you only need a foreign key value, use the foreign key value that is already on the object you’ve got, rather than getting the whole related object and taking its primary key. 不过我们实际开发中,往往需要访问到外键对象的其他属性。如果按照默认的查询方式去遍历取值,那么会造成多次的数据库查...