models.py:

class Subject(models.Model):
    SUBJECT_CHOICES = ()
    name = models.CharField(max_length=20,choices=SUBJECT_CHOICES)

    def __str__(self):
        return self.name


class Course(models.Model):

    SKILL_LEVEL_CHOICES = (
        ('Beginner', 'Beginner'),
        ('Intermediate', 'Intermediate'),
        ('Advanced', 'Advanced'),
    )

    slug = models.SlugField()
    title = models.CharField(max_length=120)
    description = models.TextField()
    allowed_memberships = models.ManyToManyField(Membership)
    created_at = models.DateTimeField(auto_now_add=True)
    subjects = models.ManyToManyField(Subject)
    skill_level = models.CharField(max_length=20,choices=SKILL_LEVEL_CHOICES, null=True)
    visited_times = models.IntegerField(default=0)


    def __str__(self):
        return self.title

    def get_absolute_url(self):
        return reverse('courses:detail', kwargs={'slug': self.slug})

    @property
    def lessons(self):
        return self.lesson_set.all().order_by('position')

    class Meta:
            ordering = ('title',)

views.py:

class CourseListView(ListView):
    model = Course
    def get_queryset(self):
        qs = super().get_queryset()
        title_contains_query = self.request.GET.get('title_contains')
        view_count_min = self.request.GET.get('view_count_min')
        view_count_max = self.request.GET.get('view_count_max')
        date_min = self.request.GET.get('date_min')
        date_max = self.request.GET.get('date_max')
        skill_level_query = self.request.GET.get('skill_level')
        if title_contains_query:
            qs = qs.filter(title__icontains=title_contains_query)
        if view_count_min:
            qs = qs.filter(visited_times__gte=view_count_min)
        if view_count_max:
            qs = qs.filter(visited_times__lte=view_count_max)
        if date_min:
            qs = qs.filter(created_at__gte=date_min)
        if date_max:
            qs = qs.filter(created_at__lte=date_max)
        if skill_level_query:
            qs = qs.filter(skill_level=skill_level_query)
        return qs