Django多层嵌套ManyToMany字段ORM操作详解

# 习题
class Problem(models.Model):
  desc = models.CharField()
  answer = models.TextField()
  is_pass = models.BooleanField(default=False, verbose_name="是否通过")

# 章节
class Chapter(models.Model):
  _id = models.IntegerField(verbose_name="编号")
  title = models.CharField()
  problem = models.ManyToManyField(Problem)
  pass_rate = models.IntegerField(verbose_name="通关率")

# 书籍  
class Book(models.Model):
  title = models.CharField()
  desc = models.TextField()
  chapter = models.ManyToManyField(Chapter,verbose_name="章节")
  speed = models.IntegerField(verbose_name="学习进度", default=0)

# 按我的理解是取问题非空的章节数
# 类似于问爷爷有几个孙子，没办法跨辈，就按一个孙子对应一个爸爸来取（有重复）
book.chapter.filter(problem___id__isnull=False).count()

  def problem_in_ladder(book, problem):
    for i in book.chapter.all():
      if problem in i.problem.all():
        return True
    return False

# 习题
class Problem(models.Model):
  desc = models.CharField()
  answer = models.TextField()
  is_pass = models.BooleanField(default=False, verbose_name="是否通过")

# 章节
class Chapter(models.Model):
  _id = models.IntegerField(verbose_name="编号")
  title = models.CharField()
  problem = models.ManyToManyField(Problem)
  pass_rate = models.IntegerField(verbose_name="通关率")
 
  @property
  def items(self):
    return self.problem.count()

  @property
  def pass_problem(self):
    return self.problem.filter(is_pass=True).count()
  
# 书籍  
class Book(models.Model):
  title = models.CharField()
  desc = models.TextField()
  chapter = models.ManyToManyField(Chapter,verbose_name="章节")
  speed = models.IntegerField(verbose_name="学习进度", default=0)
  
  @property
  def chapters(self):
    return self.chapter.count()

  @property
  def pass_count(self):
    return self.chapter.filter(problem__is_pass=True).count()

  @property
  def items(self):
    return self.chapter.filter(problem___id__isnull=False).count()

class SystemUserPushHistory(models.Model):
 
  id = models.UUIDField(default=uuid.uuid4, primary_key=True)
  host_name = models.CharField(max_length=128, null=False)
  system_username = models.CharField(max_length=128, null=False)
  method = models.CharField(max_length=32, null=False)
  is_success = models.BooleanField(default=False)
  date_create = models.DateTimeField(auto_now_add=True, editable=False)
  message = models.CharField(max_length=4096, null=True)
 
  class Meta:
    db_table = "assets_systemuser_push_history"
    ordering = ['-date_create']
 
  def __str__(self):
    ret = self.system_username + " => " + self.host_name
    return ret

>>> from django.db.models import Count 
>>> from assets.models import SystemUserPushHistory
>>> p = SystemUserPushHistory.objects.values("host_name").annotate(dcount=Count(1))
>>> p
<QuerySet [{'host_name': '点2', 'dcount': 1}, {'host_name': '点3', 'dcount': 2}, {'host_name': '点2', 'dcount': 1}, {'host_name': '点3', 'dcount': 1}]>
>>> print(p.query)
SELECT `assets_systemuser_push_history`.`host_name`, COUNT(1) AS `dcount` FROM `assets_systemuser_push_history` GROUP BY `assets_systemuser_push_history`.`host_name`, `assets_systemuser_push_history`.`date_create` ORDER BY `assets_systemuser_push_history`.`date_create` DESC