Question

在一个数据库中使用四个模型，我想计算一个课程的员工总数。

此工作代码目前计算：

课程名称，即Course01，Course02
独特课程的数量，即2门课程
每门课程的实例数，即Course01 = 3，Course02 = 1，Total courses = 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)

我想返回每个独特课程组的候选人总数，即Course01 = 24名候选人

到目前为止我所拥有的......

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

假设，按课程分组，您指的是某一天的课程（CourseDetails -instance），并且您希望按课程名称和日期查询：

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

如果您想要某个课程的参加者，无论他们何时参加，请运行

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

在特定时间范围内获取参与者人数：

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()

顺便说一下，是否有可能在同一天拥有给定课程的几个实例（例如Django 101）？如果没有，我建议你把这个组合做成独特的：

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')

跨越四个模型的查询集

1 个答案: