Problem with queryset filtering with Django’s new Prefetch option

[Tobias Abdon]

I am trying to use prefetch_related’s new Prefetch option to further filter a database query. Using debug toolbar I can see that prefetch_related is doing its job in making only three DB queries. However, I am positive that the queryset filter I’m passing in is not working. Even though I’m using the option, all of the records are being retrieved in the query.

The goal of the below code is to show a list of Chapters. For each chapter, show its lessons. For each lesson, show the logged in user’s status (complete/incomplete).

Models

class Chapter(models.Model):

    status = models.IntegerField(choices=STATUS_CHOICES, default=1)

    name = models.CharField(max_length=100)

    slug = AutoSlugField(populate_from='name')

    desc = models.TextField()

class Lesson(models.Model):

    name = models.CharField(max_length=100)

    chapter = models.ForeignKey(Chapter, related_name=‘les_chapter’)

class LessonStatus(models.Model):

    status = models.IntegerField(choices=STATUS_CHOICES, default=1)

    lesson = models.ForeignKey(Lesson, related_name="status_lesson")

    student = models.ForeignKey(User)

    chapter = models.ForeignKey(Chapter, related_name=“status_chapter")

View

def chapter_list(request, course_slug):

    course = Course.objects.get(slug=course_slug)

    chapters = Chapter.objects.filter(course=course).prefetch_related(

        Prefetch('status_chapter__lesson__chapter', queryset=LessonStatus.objects.filter(student=request.user)),

    )

    return TemplateResponse(request,

        'course/chapter_list_parent.html',

        {'chapters': chapters, 'course': course,}

    )

Template

<div id="chapters">

    {% for ch in chapters %}

        <p>{{ ch.name }}</p>

        {% for le in ch.status_chapter.all %}

            <p>lesson status: {{ le.status }}</p>

            <p>lesson name: {{ le.lesson.name }}</p>

        {% endfor %}

    {% endfor %}

</div>

When I run this code the LessonStatus is not being filtered by student=request.user. Instead, it is simply getting all LessonStatus records, including those that are for other users. 

Can anyone see if there's something wrong with the above code? Or any ideas how to troubleshoot? There are no errors generated.

[Collin Anderson]

Hi,

Try this:

chapters = Chapter.objects.filter(course=course).prefetch_related(

        Prefetch('status_chapter', queryset=LessonStatus.objects.filter(student=request.user).select_related('lesson')),

)

Otherwise, maybe the to_attr will help.

Collin