如何自定义Django自带的Admin的views

Question

开发一个网站，网站的内容被划分为不同Course，每一个Course下有一些Lesson，目前利用Django自带的Admin来添加Lesson。
Course和Lesson在数据库中有相应的表，并且Lesson有一个ForeignKey是Course。现在在Course表中有一个total_lesson的属性记录这个Course下有多少课程，想要实现在Admin中增加一节Lesson就让Course的total_lesson属性同时+1，应该怎么更改views中的函数？
数据库定义如下：

class Course(models.Model):
    course_name = models.CharField(max_length=255)
    brief = models.TextField()
    overview = models.TextField()
    classification = models.CharField(max_length=32)
    release_date = models.DateTimeField(auto_now_add=True)
    course_auth = models.CharField(max_length=255, default='admin')
    total_lesson = models.IntegerField(default=0)
    def __str__(self):
        return self.course_name


class Lesson(models.Model):
    course = models.ForeignKey(Course, on_delete=models.CASCADE)
    lesson_name = models.CharField(max_length=255)
    lesson_num = models.IntegerField()
    learn = models.TextField()
    instructions = models.TextField()
    hint = models.TextField()
    language = models.CharField(max_length=32)
    time_limit = models.CharField(max_length=16)
    memory_limit = models.CharField(max_length=16)
    def __str__(self):
        return str(self.lesson_name)

Answer 1

class Course(models.Model):
    course_name = models.CharField(max_length=255)
    brief = models.TextField()
    overview = models.TextField()
    classification = models.CharField(max_length=32)
    release_date = models.DateTimeField(auto_now_add=True)
    course_auth = models.CharField(max_length=255, default='admin')
    #total_lesson = models.IntegerField(default=0)
    def __str__(self):
        return self.course_name

    def total_lesson(self):
        return self.lesson_set.all().count()