四個模型的查詢集

Question

在單個數據庫中使用四個模型，並且我想要計算課程上的員工總數。

本工作代碼當前計算：

1. 課程名稱，即Course01，Course02
2. 獨特課程的數量，即2個療程
3. 每個療程的實例的數量，即Course01 = 3 ，Course02 = 1，總的課程= 4

models.py

class Course(models.Model): 
    name   = models.CharField(max_length=75) 

class Employee(models.Model): 
    first_name = models.CharField(max_length=75) 
    surname  = models.CharField(max_length=75) 

class CourseDetail(models.Model): 
    course  = models.ForeignKey(Course) 
    date  = models.DateField(blank=True, null=True) 
    renew_date = models.DateField(blank=True, null=True, default=None) 
    attendance = models.ManyToManyField(Employee, through='CourseDetailAttendance') 

class CourseDetailAttendance(models.Model): 
    course_details = models.ForeignKey(CourseDetail) 
    employee  = models.ForeignKey(Employee) 

我想回考生總數每一個獨特的課程組，即Course01 = 24名候選人

我有什麼那麼遠，

views.py

from django.db.models import Count 

def BetweenDates(request): 
    start_date = '2013-03-01' 
    end_date = '2013-03-30' 

    cr = CourseDetail.objects.filter(date__range=(start_date, end_date)) 
    cc_count = cr.count() 
    cc_grouped = cr.values('course__name').annotate(Count('course')) 
    cc_grouped_count = cc_grouped.count() 

    cc_attendance = ??????????? 

    context = {"cc_grouped_count": cc_grouped_count, 
      "courses_grouped": cc_grouped, 
      "date_range": cr, 
      "courses_count":cc_count, 
      "cc_attendance": cc_attendance, 
      } 
    return render_to_response('between_dates.html', context, context_instance=RequestContext(request)) 

between_dates.html

{% extends 'base.html'%} 
{% block content %} 
<h4><p>{{ cc_grouped_count }} courses delivering {{ courses_count }} course instances between {{ startdate }} and {{ enddate }}</p></h4> 
    {% for cs in courses_grouped %} 
    <div class = "news-articles ingrid in-thirds"> 
     <div class = "unit"> 
     <div class= "box"> 
      {{ cs.course__name }} 
     </div> 
     </div> 
     <div class = "unit"> 
     <div class= "box"> 
      {{ cs.course__count }} 
     </div> 
     </div> 
     <div class = "unit"> 
     <div class= "box"> 
      total number of candidates goes here {{ cc_attendance }} 
     </div> 
     </div> 
    </div> 
    {% endfor %} 

Answer 1

假設，通過課程組你的意思是在某一天（CourseDetails -instance）課程，和你想的課程名稱和日期進行查詢：

course_details = CourseDetail.objects.get(course__name='Django 101', date='2013-03-01') 
cc_attendance = CourseDetailAttendance.objects.filter(course_details=course_details).count() 

如果你想擁有給定課程的服務員，當他們參加不管，運行

course_details = CourseDetail.objects.filter(course__name='Django 101') 
cc_attendance = CourseDetailAttendance.objects.filter(course_details__in=course_details).count() 

要獲得參與者的數量，在一定時限內：

course_details = CourseDetail.objects.filter(course__name='Django 101', date__range=[start_date, end_date]) 
cc_attendance = CourseDetailAttendance.objects.filter(course_details__in=course_details).count() 

順便說一句，是否有可能在同一天有一個給定的課程（例如Django 101）的幾個實例？如果不是，我建議你讓這個組合獨一無二：

class CourseDetail(models.Model): 
    course  = models.ForeignKey(Course) 
    date  = models.DateField(blank=True, null=True) 
    renew_date = models.DateField(blank=True, null=True, default=None) 
    attendance = models.ManyToManyField(Employee, through='CourseDetailAttendance') 

    class Meta: 
     unique_together = ('course', 'date')