模型多对多关系映射-【官方】百战程序员_IT在线教育培训机构


xxxxxxxxxx
from django.db import models

class Student(models.Model):
    name = models.CharField(max_length=20)
    friends = models.ManyToManyField("self")

笔记：

会生成一个中间表，如下


xxxxxxxxxx
CREATE TABLE `test_app_student_friends` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `from_student_id` int(11) NOT NULL,
  `to_student_id` int(11) NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `test_app_student_friends_from_student_id_to_stude_7ef9880e_uniq` (`from_student_id`,`to_student_id`),
  KEY `test_app_student_fri_to_student_id_154a4deb_fk_test_app_` (`to_student_id`),
  CONSTRAINT `test_app_student_fri_from_student_id_c400b5d4_fk_test_app_` FOREIGN KEY (`from_student_id`) REFERENCES `test_app_student` (`id`),
  CONSTRAINT `test_app_student_fri_to_student_id_154a4deb_fk_test_app_` FOREIGN KEY (`to_student_id`) REFERENCES `test_app_student` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci

简易多对多


xxxxxxxxxx
class SchoolClass(models.Model):
    name = models.CharField(max_length=20)

class Teacher(models.Model):
    name = models.CharField(max_length=10)
    school_class = models.ManyToManyField(SchoolClass)

笔记：

会自动生成一个中间表，DDL语句如下：


xxxxxxxxxx
CREATE TABLE `test_app_teacher_school_class` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `teacher_id` int(11) NOT NULL,
  `schoolclass_id` int(11) NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `test_app_teacher_school__teacher_id_schoolclass_i_f52c7361_uniq` (`teacher_id`,`schoolclass_id`),
  KEY `test_app_teacher_sch_schoolclass_id_7ac34d1e_fk_test_app_` (`schoolclass_id`),
  CONSTRAINT `test_app_teacher_sch_schoolclass_id_7ac34d1e_fk_test_app_` FOREIGN KEY (`schoolclass_id`) REFERENCES `test_app_schoolclass` (`id`),
  CONSTRAINT `test_app_teacher_sch_teacher_id_8c52afbd_fk_test_app_` FOREIGN KEY (`teacher_id`) REFERENCES `test_app_teacher` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci

其中：

test_app_teacher_school_class是表名: test_app是应用名， teacher是第一个模型名，school_class是第二个模型名

自定义中间表


xxxxxxxxxx
from django.db import models

class Person(models.Model):
    first_name = models.CharField(max_length=50)
    last_name = models.CharField(max_length=50)

class Group(models.Model):
    name = models.CharField(max_length=128)
    members = models.ManyToManyField(
        Person,
        through='Membership', # 必须是 类名的字符串 ，用 '' 包裹
        through_fields=('group', 'person'),
    )

class Membership(models.Model):
    group = models.ForeignKey(Group, on_delete=models.CASCADE)
    person = models.ForeignKey(Person, on_delete=models.CASCADE)
    level = models.IntegerField(default=1)

笔记：

通过 through='Membership' 指定Membership作为中间表
通过 through_fields=('group', 'person') 指定中间模型的属性
一般需要自定义中间表时，都是有额外的字段，譬如 level = models.IntegerField(default=1)

模型一对一关系映射模型新增数据

北京市昌平区回龙观镇南店村综合商业楼2楼226室