Django 计算嵌套的 ManyToManyField 对象

Question

我有以下模型，它有 3 个类 Project、CrawlerProject、CrawlerResults

class CrawlerProject(models.Model):
    user = models.ForeignKey(User,on_delete=models.SET_NULL,null=True)
    cralwer_results_M2M = models.ManyToManyField(CrawlerResults,blank=True)

class Project(models.Model):
    user = models.ForeignKey(User,on_delete=models.SET_NULL,null=True)
    crawler_project_M2M = models.ManyToManyField(CrawlerProject,blank=True)

在这里，我想计算单个 Project 对象中所有 CrawlerProjects 的 CrawlerResults 对象的总数。

projects = Project.objects.all().prefetch_related('crawler_project_M2M')
for each_proj in projects:
   total_num_of_crawler_results = each_proj.crawler_project_M2M__cralwer_results_M2M.count() ## count all the crawler_results objects of all crawler_project present in current `project` object.

如何以高效的方式(单个查询)获取嵌套的 ManyToMany 类的总数？

Answer 1

试试这个:

from django.db.models import Count
CrawlerProjects =CrawlerProject.objects.all().annotate(CrawlerResults_count=Count('project'))