Django从注释计数中排除 [英] Django exclude from annotation count

问题描述

我有以下应用程序：

 从django.db导入模型
 
 
 class Worker（models.Model）：
 name = models.CharField（max_length = 60）
 
 def __str __（self）：
 return self.name 
 
 
 class Job（models.Model）：
 worker = models.ForeignKey（Worker）
 is_completed = models.BooleanField（）
  pre> 
 
 
我想用已完成作业的计数注释Workers查询。
 
 
 
我会尝试使用以下脚本：
  from myapp.models import Worker，Job 
 from django.db.models import Count 
 
w = Worker.objects.create（name ='Worker1'）
 Job.objects.create（worker = w，is_completed = False）
 Job.objects.create（worker = w ，is_completed = False）
 Job.objects.create（worker = w，is_completed = True）
 Job.objects.create（worker = w，is_completed = True）
 
工人= Worker.objects.all（）。annotate（num_jobs = Count（'job'））
 worker s [0] .num_jobs 
＃>>>> 4 
 workers = Worker.objects.all（）。exclude（job__is_completed = False）.annotate（num_jobs = Count（'job'））
＃>>> [] 
  
最后一个查询的结果为空。如何从反向关系中排除元素？
 
 
 
 Django 1.8，python 2.7 
 
 
 
  UPD。 strong>我想让所有的工作人员都在queryset，即使是那些没有工作的人。
解决方案
  update ：好的，我用这个玩了一些产生解决方案，我想我用条件表达式：
 
 
条件表达式允许您使用if ... elif ... else逻辑
过滤器，注释，聚合和更新。条件
表达式计算表
的每一行的一系列条件，并返回匹配的结果表达式。
 
 
 
 
 <注意： 条件表达式 （例如<由@Pynchia指出，code>案例和当）在Django 1.8 中是 
 
 
 从django.db.models导入IntegerField，Sum，Case，当
 
 workers = Worker.objects。注释（
 num_jobs = Sum（
 Case（
 When（job__is_completed = True，then = 1））
 default = 0，
 output_field = IntegerField（）
）
）
）
  
现在，每个工作人员都会有一个num_jobs这将是一个整数，显示工作人员有多少完成的工作：）
 
I have following application:
from django.db import models


class Worker(models.Model):
    name = models.CharField(max_length=60)

    def __str__(self):
        return self.name


class Job(models.Model):
    worker = models.ForeignKey(Worker)
    is_completed = models.BooleanField()
I want to annotate Workers query with count of completed jobs.

I'll try to do it with following script:
from myapp.models import Worker, Job
from django.db.models import Count

w = Worker.objects.create(name='Worker1')
Job.objects.create(worker=w, is_completed=False)
Job.objects.create(worker=w, is_completed=False)
Job.objects.create(worker=w, is_completed=True)
Job.objects.create(worker=w, is_completed=True)

workers = Worker.objects.all().annotate(num_jobs=Count('job'))
workers[0].num_jobs    
# >>> 4
workers = Worker.objects.all().exclude(job__is_completed=False).annotate(num_jobs=Count('job'))
# >>> []
Result of the last query is empty. How to exclude elements from reverse relation?

Django 1.8, python 2.7

UPD. I would like to have all workers in queryset, even those, who has a zero jobs
解决方案
update: ok I played a bit with this to generate the solution and I think I got it using Conditional Expressions:

  
Conditional expressions let you use if ... elif ... else logic within
  filters, annotations, aggregations, and updates. A conditional
  expression evaluates a series of conditions for each row of a table
  and returns the matching result expression.
Note: Conditional Expressions (such as Case and When) are new in Django 1.8, as pointed out by @Pynchia
from django.db.models import IntegerField, Sum, Case, When

workers = Worker.objects.annotate(
              num_jobs=Sum(
                  Case(
                      When(job__is_completed=True, then=1),
                      default=0,  
                      output_field=IntegerField()
                  )
               )
           )
now, each worker will have a num_jobs which will be an Integer that shows how many completed jobs that worker has :)

                        
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