django - 如何綁定另一個表中計算的計數值的表記錄

Question

在我的應用程序中，我有一個培訓列表。此列表中的一個字段應顯示每個培訓的預訂數量。 爲了說明我的意思我準備的SQL查詢：

SELECT * 
FROM club_training a 
LEFT JOIN 
(SELECT training_id, count(*) 
FROM club_booking 
group by training_id) b 
ON a.id = b.training_id 

你能不能給我一些建議如何做到這一點在Django？ 我在我的代碼中使用了Booking.objects.all().values('training_id').annotate(booked_amount=Count('training_id'))，但結果是所有培訓的所有計數值都顯示在列表上的每個培訓中。應顯示一個適合每次培訓的計數值。

views.py

class HomePageView(TemplateView): 
    """Home Page with list of trainings""" 
    template_name = 'club/training_list.html' 


    def get_context_data(self, **kwargs): 
     now = datetime.datetime.now() 
     context = super(HomePageView, self).get_context_data(**kwargs) 
     context['trainings'] = Training.objects.filter(state="A", training_date__gte=now).order_by('training_date', 'start_time') 
     for each_training in context['trainings']:  
      each_training.diff = each_training.availability - each_training.counter 
      each_training.counter = Booking.objects.all().values('training_id').annotate(booked_amount=Count('training_id')) 
     return context 

models.py

class Training(models.Model): 
    """Class for plan training""" 
    STATE = (
     ('A', 'Active'), 
     ('I', 'Inactive'), 
    ) 
    name = models.ForeignKey('TrnDesc') 
    instructor = models.ForeignKey('Instructor') 
    start_time = models.TimeField(blank=True) 
    end_time = models.TimeField(default='00:00:00') 
    availability = models.PositiveIntegerField(default=15) 
    state = models.CharField(max_length=1, choices=STATE, default='A') 
    training_date = models.DateField(default=date.today) 
    counter = models.PositiveIntegerField(default=0) 
    def __str__(self): 
     return self.name.name 

class Booking(models.Model): 
    """Data of people which book fitness classes""" 
    first_name = models.CharField(max_length=50) 
    last_name = models.CharField(max_length=50) 
    email = models.CharField(max_length=50) 
    phone = models.CharField(max_length=10) 
    training = models.ForeignKey('Training') 
    def __str__(self): 
     return self.training.name.name 

training_list.html

{% extends 'club/base.html' %} 

{% block content %} 

     <ul class="nav nav-pills"> 
      <li role="presentation" class="active"><a href="#">Fitness Classes</a></li> 
      <li role="presentation"><a href="#">Join Us</a></li> 
      <li role="presentation"><a href="#">Contact Us</a></li> 
     </ul> 
     <br></br> 
    {% regroup trainings by training_date as date_list %} 
    {% for date in date_list %} 
     <div class="panel panel-default"> 


      <div class="panel-heading">{{date.grouper|date:"l, d F o"}}</div> 


      <table class="table"> 
       <tr> 
        <th style="width: 20%">Training name</th> 
        <th style="width: 30%">Training description</th> 
        <th style="width: 10%">Instructor</th> 
        <th style="width: 10%">Start time</th> 
        <th style="width: 10%">End time</th> 
        <th style="width: 10%">Left</th> 
        <th style="width: 10%">Test_counter</th> 
        <th style="width: 10%">Actions</th> 
       </tr> 


       {% for training in date.list %} 

       <tr> 
        <td>{{training.name}}</td> 
        <td>{{training.name.desc}}</td> 
        <td>{{training.instructor}}</td> 
        <td>{{training.start_time|time:"H:i"}}</td> 
        <td>{{training.end_time|time:"H:i"}}</td> 
        <td>{{training.diff}}</td> 
        <td>{{training.counter}}</td> 
        <td><a href="{% url 'book' training_id=training.pk%}"><button type="button" class="btn btn-primary">Book</button></a></td> 
       </tr> 

       {% endfor %}  
      </table> 
     </div> 
    {% endfor %} 

{% endblock %} 

Answer 1

for each_training in context['trainings']:  
     each_training.diff = each_training.availability - each_training.counter 
     each_training.counter = Booking.objects.filter(training_id=each_training.id).count() # just modify this line 
    return context 

Answer 2

我想從另一個方向的方法：each_training.booking_set.count()

而且，我不知道它適合你的數據庫的目標，但如果我明白你在找什麼，你可以設置它是這樣的：

models.py

class Training(models.Model): 
    ... 
    <fields> 
    ... 
    def __str__(self): 
     return self.name.name 

    @property 
    def counter(self): 
     return self.booking_set.count() 

    @property 
    def diff(self): 
     return self.availability - self.counter 

像這樣，值可以直接從模型轉到模板。

我能看到的唯一問題是我認爲它阻止了這些字段成爲查詢集的一部分。例如，Training.objects.filter(counter__gt=0)將不起作用。如果你需要的話，我認爲你仍然必須找到一個機會來保存和更新數據庫中的值，possibly using a signal，這樣每次調用視圖時都不必一次又一次地保存值。

它也像你可以使用一個經理來處理一些您可以在視圖都在做邏輯：

managers.py

from django.db.models import Manager 

class Active(Manager): 

    def by_date(self, date) 
     Training.objects.filter(state="A", training_date__gte=date).order_by('training_date', 'start_time') 

然後你可以經理添加到您的模型（即一定要保持你的香草經理）：

models.py

from .managers import Courses 

class Training(models.Model): 
    ... 
    <fields> 
    objects = models.Manager() 
    active = Active() 
    ... 

    def __str__(self): 
     return self.name.name 

現在，您可以使用纖細的ListView分發所有信息。

from django.views.generic import ListView 

class HomePageView(ListView): 
    """Home Page with list of trainings""" 
    template_name = 'club/training_list.html' 
    context_object_name = "trainings" 

    def get_queryset(self): 
     now = datetime.datetime.now() 
     return Trainings.active.by_date(now) 

我不熟悉你在模板中做的一些事情，但是一切都應該像現在一樣工作。

或許我的路要走，但我希望它的一些好的精神食糧:)