Django模型一对多关系

ForeignKey 一对多

创建模型Classes,Students 一个班级对应多个学生

from django.db import models

# 一对多关系
# 班级表
class Classes(models.Model):
    cname = models.CharField(max_length=15)

    class Meta():
        db_table = 'classes'

# 学生表
class Students(models.Model):
    sname = models.CharField(max_length=15)
    # 在学生表中关联班级表,班级表的一条数据关联学生表中的多条数据
    cid = models.ForeignKey(to='Classes', to_field='id', on_delete=models.CASCADE)
        # 第一个参数：是被关联的模型名称
        # 第二个参数：是被关联的模型(表)名称的字段
        # 第三个参数：当被关联的班级表classes中的一条数据被删除的时候,与之关联的学生表students中的所有数据也会被删除(必需)

    class Meta():
        db_table = 'students'
    

根路由

from django.contrib import admin
from django.urls import path, include

urlpatterns = [
    path('admin/', admin.site.urls),
    path('app/', include('myapp.urls')),
]

子路由

from django.urls import path, re_path
from . import views

urlpatterns = [
    path('otm_add_01/', views.onetomany_add_01),
    path('otm_add_02/', views.onetomany_add_02),
    path('otm_update/', views.onetomany_update),
    path('otm_search/', views.onetomany_search),
    path('otm_delete/', views.onetomany_delete),
]

视图

from django.http import HttpResponse
from . import models

# 一对多
# 增
def onetomany_add_01(request):
    # 在添加班级时添加学生
    # 添加班级
    class_01 = models.Classes()
    class_01.cname = 'class17'
    class_01.save()
    class_02 = models.Classes()
    class_02.cname = 'class18'
    class_02.save()

    # 添加学生并关联班级
    student_01 = models.Students()
    student_01.sname = 'student1701'
    # 关联班级
    student_01.cid = class_01

    student_02 = models.Students()
    student_02.sname = 'student1702'
    student_02.cid = class_01

    student_03 = models.Students()
    student_03.sname = 'student1801'
    student_03.cid = class_02

    student_04 = models.Students()
    student_04.sname = 'student1802'
    student_04.cid = class_02

    student_01.save()
    student_02.save()
    student_03.save()
    student_04.save()

    return HttpResponse('<script>alert("success");</script>')

def onetomany_add_02(request):
    # 已有班级添加学生
    class_03 = models.Classes.objects.all().get(id=3)
    student_05 = models.Students()
    student_05.sname = 'student1901'
    student_05.cid = class_03
    student_05.save()

    return HttpResponse('<script>alert("success");</script>')

# 查
def onetomany_search(request):
    # 通过学生查找班级
    studentobj = models.Students.objects.all().get(id=1)
    print(studentobj.sname)
    # 学生对象.外键.班级信息
    print(studentobj.cid.cname)

    # 通过班级查找学生
    classobj = models.Classes.objects.all().get(cname='class19')
    print(classobj.cname)
    # 班级对象.学生类名(小写)_set.学生属性
    print(classobj.students_set.all().values())

    return HttpResponse('<script>alert("success");</script>')

# 改
def onetomany_update(request):
    # 获取要转移到的班级并改名
    tran_class = models.Classes.objects.all().get(cname='class19')
    tran_class.cname = 'class_19'
    tran_class.save()
    # 通过学生对象修改学生信息并转移班级
    tran_student = models.Students.objects.all().get(id=1)
    tran_student.sname = 'student19_01'
    tran_student.cid = tran_class
    tran_student.save()
    # 通过班级对象修改学生信息
    update_student = tran_class.students_set.all().last()
    update_student.sname = 'student1902'
    update_student.save()

    return HttpResponse('<script>alert("success");</script>')

# 删
def onetomany_delete(request):
    # 如果删除班级,与之关联的学生也会被删除
    delete_class = models.Classes.objects.all().get(id=4)
    delete_class.delete()
    # 如果删除学生,与之关联的班级不会有影响
    delete_student = models.Students.objects.all().get(id=8)
    delete_student.delete()

    return HttpResponse('<script>alert("success");</script>')