-Many-to-Many
*** 指定了中间表，add，remove，set 都不能用，必须用中间表
两端都可以自动获得另一端的自动API访问。跟一对多的反向访问类似。但是使用的是本字段的字段名
In [112]: Course.objects.create(name=‘python全栈‘) Out[112]: <Course: python全栈> In [113]: Course.objects.create(name=‘python全套‘) Out[113]: <Course: python全套> In [114]: Course.objects.create(name=‘English‘) Out[114]: <Course: English> In [115]: c1,c2,c3= Course.objects.all() In [116]: c1 Out[116]: <Course: python全栈> In [117]: c2 Out[117]: <Course: python全套> In [118]: c3 Out[118]: <Course: English>
In [4]: c1,c2,c3= Course.objects.all()
In [5]: s1,s2,s3,s4,s5,s6 = Student.objects.all()
In [6]: c1.students.all() #正向，students为course的字段，也是一个管理器
Out[6]: <QuerySet [<Student: 1-心蓝-0>]>
In [7]: s1.course_set.all() #反向查询
Out[7]: <QuerySet [<Course: python全栈>]>
#如果没有中间表下面的正向添加、删除实例可以使用，这里不做演示 #指定了中间表后set,add,remove都不能用
c1.students.add(s1,s2,s3,s4,s5,s6)
c1.students.remove(s3,s4,s5,s6)
#如果没有中间表，下面的反向添加、删除实例可以使用，不做演示了 #只要是反向，就是用模型的小写加_set
s1.course_set.add(c1,c2,c3)
s1.course_set.remove(c1,c2,c3)
#加了中间表以后的操作
e =Enroll()
e.course = c1
e.student = s1
e.save()
或者
e =Enroll()
e.course_id = c1.id
e.student_id = s1.id
e.save()
2.增加
In [13]: Enroll.objects.create(student=s3,course=c3)
Out[13]: <Enroll: Enroll object (3)>
In [14]: Enroll.objects.create(student=s6,course=c2)
Out[14]: <Enroll: Enroll object (4)>
In [15]: Enroll.objects.create(student=s7,course=c1)
Out[15]: <Enroll: Enroll object (5)>
-One-to-One
正向访问：
In [8]: sd = StudentDetail.objects.create(num=‘20190228‘,college=‘家里蹲‘,student=s1) In [9]: sd.student Out[9]: <Student: 1-心蓝-0> In [10]: sd.student.name Out[10]: ‘心蓝‘ In [11]: sd.student.age Out[11]: 0
反向（通过模型的小写）
In [12]: s1.studentdetail Out[12]: <StudentDetail: StudentDetail object (1)> In [13]: s1.studentdetail.num Out[13]: ‘20190228‘ In [14]: s1.studentdetail.college Out[14]: ‘家里蹲‘
3. 跨表查询（跨模型的相关字段的字段名，并且用__链接）
例一：查询男生报名了什么课程
In [19]: res = Course.objects.filter(students__sex =1) #正向，students为字段 In [20]: print(res.query) SELECT `teacher_course`.`id`, `teacher_course`.`name` FROM `teacher_course` INNER JOIN `teacher_enroll` ON (`teacher_course`.`id` = `teacher_enroll`.`course_id`) INNER JOIN `teacher_student` ON (`teacher_enroll`.`student_id` = `teacher_student`.`id`) WHERE `teacher_student`.`sex` = 1 In [21]: res Out[21]: <QuerySet [<Course: python全栈>]>
例二：查询所有报名python课程的学生
反向关系，使用模型的小写course__name__contains
In [24]: res = Student.objects.filter(course__name__contains=‘python‘) #course为模型的小写 In [25]: print(res.query) SELECT `teacher_student`.`id`, `teacher_student`.`name`, `teacher_student`.`age`, `teacher_student`.`sex`, `teacher_student`.`qq`, `teacher_student`.`phone`, `teacher_student`.`grade_id`, `teacher_student`.`c_time`, `teacher_student`.`e_time` FROM `teacher_student` INNER JOIN `teacher_enroll` ON (`teacher_student`.`id` = `teacher_enroll`.`student_id`) INNER JOIN `teacher_course` ON (`teacher_enroll`.`course_id` = `teacher_course`.`id`) WHERE `teacher_course`.`name` LIKE BINARY %python% In [26]: res Out[26]: <QuerySet [<Student: 1-心蓝-0>]>
例三：查询所有报名了python课程的33期的学员
In [28]: res = Student.objects.filter(course__name__contains= ‘python‘,grade__num__contains=‘33‘) #course为反向，grade为正向 In [29]: print(res.query) SELECT `teacher_student`.`id`, `teacher_student`.`name`, `teacher_student`.`age`, `teacher_student`.`sex`, `teacher_student`.`qq`, `teacher_student`.`phone`, `teacher_student`.`grade_id`, `teacher_student`.`c_time`, `teacher_student`.`e_time` FROM `teacher_student` INNER JOIN `teacher_enroll` ON (`teacher_student`.`id` = `teacher_enroll`.`student_id`) INNER JOIN `teacher_course` ON (`teacher_enroll`.`course_id` = `teacher_course`.`id`) INNER JOIN `teacher_grade` ON (`teacher_student`.`grade_id` = `teacher_grade`.`id`) WHERE (`teacher_course`.`name` LIKE BINARY %python% AND `teacher_grade`.`num` LIKE BINARY %33%) In [30]: res Out[30]: <QuerySet []>
例四：查询缴费小于3000的学员
In [31]: res = Student.objects.filter(enroll__pay__lt=3000) In [32]: print(res.query) SELECT `teacher_student`.`id`, `teacher_student`.`name`, `teacher_student`.`age`, `teacher_student`.`sex`, `teacher_student`.`qq`, `teacher_student`.`phone`, `teacher_student`.`grade_id`, `teacher_student`.`c_time`, `teacher_student`.`e_time` FROM `teacher_student` INNER JOIN `teacher_enroll` ON (`teacher_student`.`id` = `teacher_enroll`.`student_id`) WHERE `teacher_enroll`.`pay` < 3000.0 In [33]: res Out[33]: <QuerySet [<Student: 1-心蓝-0>]>
例五：查询报名了python课程所在的班级
In [35]: res = Grade.objects.filter(student__course__name__contains= ‘python‘) In [36]: print(res.query) SELECT `teacher_grade`.`id`, `teacher_grade`.`name`, `teacher_grade`.`num` FROM `teacher_grade` INNER JOIN `teacher_student` ON (`teacher_grade`.`id` = `teacher_student`.`grade_id`) INNER JOIN `teacher_enroll` ON (`teacher_student`.`id` = `teacher_enroll`.`student_id`) INNER JOIN `teacher_course` ON (`teacher_enroll`.`course_id` = `teacher_course`.`id`) WHERE `teacher_course`.`name` LIKE BINARY %python% In [37]: res Out[37]: <QuerySet [<Grade: 40期 - 进阶>]>
value 与only的区别
value返回字典
only返回对象
In [40]: res=Student.objects.values(‘name‘)
In [41]: res
Out[41]: <QuerySet [{‘name‘: ‘心蓝‘}, {‘name‘: ‘litao‘}, {‘name‘: ‘梦洁‘}, {‘name‘: ‘魏明凯‘}, {‘name‘: ‘litao‘}, {‘name‘: ‘刘洋‘}]>
In [42]: type(res[0])
Out[42]: dict
In [43]: res[0]
Out[43]: {‘name‘: ‘心蓝‘}
In [44]: res=Student.objects.only(‘name‘)
In [45]: res
Out[45]: <QuerySet [<Student: 1-心蓝-0>, <Student: 2-litao-0>, <Student: 3-梦洁-0>, <Student: 4-魏明凯-0>, <Student: 5-litao-0>, <Student: 6-刘洋-0>]>
In [46]: res[0].id
Out[46]: 1
In [47]: res[0]
Out[47]: <Student: 1-心蓝-0>
原文地址：https://www.cnblogs.com/taoge188/p/10506760.html