python测试开发django-38.多对多（ManyToManyField）查询

前言

一个学生可以对应多个老师，一个老师也可以教多个学生，这就是一种多对多的关系

models建表

新建一个老师表Teacher，和一个学生表Student

class Teacher(models.Model):
    '''老师表'''
    teacher_name = models.CharField(max_length=30, verbose_name="老师", default="")
    tel = models.CharField(max_length=30, verbose_name="电话", default="")
    mail = models.CharField(max_length=30, verbose_name="邮箱", default="")

    class Meta:
        verbose_name = "老师"
        verbose_name_plural = verbose_name


class Student(models.Model):
    '''学生表'''
    student_id = models.CharField(max_length=30, verbose_name="学号", default="")
    name = models.CharField(max_length=30, verbose_name="姓名", default="")
    age = models.IntegerField(verbose_name="年龄",  default="")
    # 多对多
    teachers = models.ManyToManyField(Teacher)

    class Meta:
        verbose_name = "学生"
        verbose_name_plural = verbose_name

之后执行 makemigrations 和migrate，同步数据

python manage.py makemigrations
python manage.py migrate

同步之后数据库里面会新增三张表：student、teacher、teacher_students

shell模式新增数据

为了调试方便，可以使用django的shell模式，对表的数据增删改查操作，打开cmd，cd到manage.py目录

python manage.py shell

多对多表的增加数据

>>> from hello.models import Teacher, Student
>>> t1=Teacher.objects.create(teacher_name='刘老师',tel='155300001111',mail='[email protected]')
>>> t1.save()
>>> t1
<Teacher: Teacher object (1)>
>>> t2=Teacher.objects.create(teacher_name='万老师',tel='155300001112',mail='[email protected]')
>>> t2.save()
>>> t2
<Teacher: Teacher object (2)>
>>> s1=Student.objects.create(student_id='11002200',name='张三',age=19)
>>> s1.save()

# 方法一：添加id
# 可以添加Teacher对应的id
>>> s1.teachers.add(1)
# 也可以添加多个id，逗号隔开
>>> s1.teachers.add(1,2)
# 如果添加的是传一个可迭代对象(list或tupule),可以用*分开传入这种方法
>>> s1.teachers.add(*[1,2])

# 方法二、直接添加对象
>>> s1.teachers.add(t1)
>>> s1.teachers.add(t2)
>>> s1.teachers.add(t1,t2)

# 也可以先查询需要添加的对象
>>> ob=Teacher.objects.get(teacher_name='刘老师')
>>> ob
<Teacher: Teacher object (1)>
>>> s2=Student.objects.create(student_id='11002201',name='李四',age=19)
>>> s2.teachers.add(ob)

正向查询

通过student表对象，查询到对应的teacher

>>> from hello.models import Teacher, Student
>>> stu=Student.objects.filter(name='李四').first()
>>> stu
<Student: Student object (2)>
>>> stu.student_id
'11002201'

# 正向查询
>>> stu.teachers.all()
<QuerySet [<Teacher: Teacher object (1)>]>

>>> stu.teachers.all()[0].teacher_name
'刘老师'
>>> stu.teachers.all()[0].tel
'155300001111'

反向查询_set

通过老师名称，查询对应关联的学生，反向查询的时候在关联表名称后面加_set，如果设置related_name参数，就用related_name参数对应名称查询
参考上一篇https://www.cnblogs.com/yoyoketang/p/10573218.html

>>> tea=Teacher.objects.filter(teacher_name='刘老师').first()
>>> tea
<Teacher: Teacher object (1)>
>>> tea.tel
'155300001111'

# 反向查询
>>> tea.student_set.all()
<QuerySet [<Student: Student object (1)>, <Student: Student object (2)>]>
>>> tea.student_set.all()[0].name
'张三'
>>>