# 关联外键    

sgrade = models.ForeignKey("Grades",on_delete=models.CASCADE)

版本跟新后忘记加on_delete=models.CASCADE

报错困扰了很久 多读报错信息

from django.db import models

# Create your models here.
class Grades(models.Model):
    gname = models.CharField(max_length=20)
    gdate = models.DateTimeField()
    ggirlnum = models.IntegerField()
    gboynum = models.IntegerField()
    isDelete = models.BooleanField(default=False)
    def __str__(self):
        return self.gname
    class Meta:
        db_table = "grades"
#
class StudentsManager(models.Manager):
    def get_queryset(self):
        return super(StudentsManager,self).get_queryset().filter(isDelete=False)


class Students(models.Model):
    #自定义模型管理器
    #当自定义模型管理器，object就不存在了
    stuObj =models.Manager()
    stuObj2=StudentsManager()
    sname = models.CharField(max_length=20)
    sgender = models.BooleanField(default=True)
    sage = models.IntegerField(db_column='age')
    scontend = models.CharField(max_length=20)
    isDelete = models.BooleanField(default=False)
    #关联外键
    sgrade = models.ForeignKey("Grades",on_delete=models.CASCADE)
    def __str__(self):
        return self.sname
    # lastTime = models.DateTimeField(auto_created=True)
    # createTime = models.DateTimeField(auto_created=True)
    class Meta:
        db_table = "students"
        ordering = ['id']