Django filtering objects from a filtered foreignkey object

Question

I'm trying to filter a list of lectures which have a foreignkey relation with a model called content. Basically every lecture is related to a specific content. But I'm stuck. below is my code:

models.py

class CourseContent(models.Model):
    title = models.CharField(max_length = 250)
    course = models.ForeignKey(Course, on_delete = models.CASCADE, null = True)

    def __str__(self):
        return self.title

class CourseLecture(models.Model):
    content = models.ForeignKey(CourseContent, on_delete = models.CASCADE, null = True)
    title = models.CharField(max_length = 50)
    file = models.FileField()

    def __str__(self):
        return self.title

views.py

def coursedetails(request, pk):
    course = Course.objects.get(id = pk)
    content = CourseContent.objects.filter(course = course)
    content_ids = content.values_list('id')
    lectures = CourseLecture.objects.filter(content__in = content_ids)
    reviews = course.review_set.all()
    rev_count = reviews.count()
    avg = reviews.aggregate(avg = Avg('rating'))
    total = reviews.aggregate(sum = Sum('rating'))
    print(content_ids)
    return render(request, "main/course_detail_view.html", {"course": course, "lectures": lectures, "content": content , "reviews": reviews, "rev_count": rev_count, "avg": avg, "total": total})

The problem here is that i cannot filter lectures on basis of specific content ids. The objects filtered is showing in all the content rather than showing in their specific section.

Thanks in advance.

ruddra · Accepted Answer · 2020-05-21 07:32:36Z

1

The above implementation should work, but it is not efficient. Here is how I would do:

lectures = CourseLecture.objects.filter(content__course_id = pk)

If you mean to order the lectures by content_id, then just add order_by:

lectures = CourseLecture.objects.filter(content__course_id = pk).order_by('content')

Finally, if you want to show the lectures respect to each content, then probably use the following template code:

{% for c in content %}
    {{ c.title }}
    {% for lecture in c.courselecture_set.all %}
       {{ lecture.title }}
     {% endfor %}
{% endfor %}

answered May 21, 2020 at 7:32

ruddra

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Abhishek J · Accepted Answer · 2020-05-21 07:32:52Z

0

Try and replace the line with

lectures = CourseLecture.objects.filter(content__pk__in = content_ids)

Refer this Django: What is the correct way to query by foreign key field's id? for more.

answered May 21, 2020 at 7:32

Abhishek J

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Comments

Shubham Gupta - TCH · Accepted Answer · 2020-05-21 07:36:25Z

0

You can use related_name in your Foreign Key. So, it will be like:

then you can just use Course.lecture.all(). And it will give you all of the lectures with that Course Foreign Key.

Eg:

class Airport(models.Model):
    city = models.CharField(max_length=64)
    code = models.CharField(max_length=4)

class Flights(models.Model):
    origin = models.ForeignKey(Airport, on_delete=models.PROTECT, related_name="origin")
    destination= models.ForeignKey(Airport, on_delete=models.PROTECT, related_name="destination")
    duration = models.IntegerField()

So, Airport.objects.get(pk=1).origin.all() will give me all Flights that Originate from Airport with Primary Key 1.

Hope this Helps.

answered May 21, 2020 at 7:36

Shubham Gupta - TCH

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