Django------->>>modle

import os

os.environ.setdefault("DJANGO_SETTINGS_MODULE", "modletest.settings")
import django

django.setup()

from  apptest import models

# 正向查找

# models.Students.objects.filter(sclass="一班") #这句是错的,ValueError: invalid literal for int() with base 10: '一班'

# obj=models.Students.objects.filter(sclass__cname="一班")  #筛选出一班的学生
# obj = obj.first() #得到第一个结果
# obj.sclass #得到sclass的一个对象
# obj.sclass.cname

# 反向查找

# obj = models.Classes.objects.filter(students__sname="张三")
# obj=obj[0]
# obj=obj.students_set.all()  # <QuerySet [<Students: 张三>, <Students: 李四>]>
# obj.first().sname  #得到张三所在班级的第一个学生的名字

obj = models.Teachers.objects.all().values('teacher_to_class__cls__cname')  # 可以通过第三张表进行查询
obj = models.Teachers.objects.filter(tname="张三")
obj = obj[0]
print(obj.teacher_to_class_set.all())  # <QuerySet [<Teacher_to_Class: 1>, <Teacher_to_Class: 5>]>
obj.teacher_to_class_set.all()[0].cls_id.cname

# In [9]: obj.teacher_to_class_set.all()[0].cls
# Out[9]: <Classes: 一班>
#
# In [10]: obj.teacher_to_class_set.all()[0].cls.cname
# Out[10]: '一班'
#
# In [11]: obj.teacher_to_class_set.all()[0].teacher
# Out[11]: <Teachers: 张三>

from django.db import models

# Create your models here.

class Students(models.Model):
    sname = models.CharField(max_length=50)
    sclass = models.ForeignKey('Classes')

    def __str__(self):
        return self.sname

class Classes(models.Model):
    cname = models.CharField(max_length=50)

    def __str__(self):
        return self.cname

class Teachers(models.Model):
    tname = models.CharField(max_length=50)

    def __str__(self):
        return self.tname

class Teacher_to_Class(models.Model):
    teacher = models.ForeignKey("Teachers")
    cls = models.ForeignKey("Classes")

    class Meta:
        unique_together = (('teacher', 'cls'))

    def __str__(self):
        return str(self.id)

 obj=models.Teachers.objects.all()[0]
 print(obj.cls.all())

 obj = models .Classes .objects.all()[0]
 print(obj.teachers_set )  #apptest.Teachers.None
 print(obj.teachers_set.filter(tname="张三"))

 class Teachers(models.Model):
     tname = models.CharField(max_length=50)
     cls = models.ManyToManyField("Classes")

     def __str__(self):
         return self.tname

import os

os.environ.setdefault("DJANGO_SETTINGS_MODULE", "modletest.settings")
import django

django.setup()

from  apptest import models

# 正向查找

# models.Students.objects.filter(sclass="一班") #这句是错的,ValueError: invalid literal for int() with base 10: '一班'

# obj=models.Students.objects.filter(sclass__cname="一班")  #筛选出一班的学生
# obj = obj.first() #得到第一个结果
# obj.sclass #得到sclass的一个对象
# obj.sclass.cname

# 反向查找

# obj = models.Classes.objects.filter(students__sname="张三")
# obj=obj[0]
# obj=obj.students_set.all()  # <QuerySet [<Students: 张三>, <Students: 李四>]>
# obj.first().sname  #得到张三所在班级的第一个学生的名字

obj = models.Teachers.objects.all().values('teacher_to_class__cls__cname')  # 可以通过第三张表进行查询
obj = models.Teachers.objects.filter(tname="张三")
obj = obj[]
print(obj.teacher_to_class_set.all())  # <QuerySet [<Teacher_to_Class: 1>, <Teacher_to_Class: 5>]>
obj.teacher_to_class_set.all()[].cls_id.cname

# In [9]: obj.teacher_to_class_set.all()[0].cls
# Out[9]: <Classes: 一班>
#
# In [10]: obj.teacher_to_class_set.all()[0].cls.cname
# Out[10]: '一班'
#
# In [11]: obj.teacher_to_class_set.all()[0].teacher
# Out[11]: <Teachers: 张三>