title: django-filter custom filter not get queryset
body: <p><strong>First of all, I'm beginner in Django-filter if you could offer best solution, I'll be glad to hear it.</strong></p>
  
  <p>I need to filter QuerySet by ForignKeys' fields. And exactly <code>author</code> and <code>worker</code>.</p>
  
  <h2>Model.py</h2>
  
  <pre><code>class Object(models.Model):
      class Meta:
          abstract = True
  
      author = models.ForeignKey('Users.User', on_delete=models.CASCADE)
  
  
  class Task(Object):
      priority_choices = (
          ('high', 'Высокий'),
          ('middle', 'Стандартный'),
          ('low', 'Низкий'),
      )
  
      status_choices = (
          ('open', 'Открыта'),
          ('done', 'Выполнена'),
          ('close', 'Закрыта'),
      )
  
      name = models.CharField(max_length=140)
      description = models.TextField()
      end_date = models.DateField()
      worker = models.ForeignKey('Users.User', on_delete=models.CASCADE, related_name='worker_set')
      priority = models.CharField(max_length=15, choices=priority_choices)
      status = models.CharField(max_length=15, choices=status_choices)
  </code></pre>
  
  <h2>Filters.py</h2>
  
  <pre><code>class TaskFilter(filters.FilterSet):
      my_tasks = filters.BooleanFilter(
          label="Мои задачи",
          method='my_task_filter',
          widget=forms.CheckboxInput()
      )
      tasks_for_me = filters.BooleanFilter(
          label="Задачи для меня",
          method='tasks_for_me_filter',
          widget=forms.CheckboxInput()
      )
      commented_tasks = filters.BooleanFilter(
          label="Я комментировал",
          method='commented_tasks_filter',
          widget=forms.CheckboxInput())
  
      class Meta:
          model = Task
          fields = ['my_tasks', 'tasks_for_me', 'commented_tasks']
  
      def my_task_filter(self, queryset, name, value):
          print(1, self, queryset, name, value)
          return queryset.filter(author_id=self.request.user.id)
  
      def tasks_for_me_filter(self, queryset, name, value):
          print(2, self, queryset, name, value)
          return queryset.filter(worker_id=self.request.user.id)
  
      def commented_tasks_filter(self, queryset, name, value):
          print(3, self, queryset, name, value)
          return queryset.filter(comment__author_id=self.request.user.id)
  </code></pre>
  
  <p>According to prints in <strong>filters.py</strong> I get:</p>
  
  <pre><code>1 &lt;TaskManager.filters.TaskFilter object at 0x7f87290dea90&gt; &lt;QuerySet [&lt;Task: Task object&gt;, &lt;Task: Task object&gt;, &lt;Task: Task object&gt;]&gt; my_tasks False
  2 &lt;TaskManager.filters.TaskFilter object at 0x7f87290dea90&gt; &lt;QuerySet []&gt; tasks_for_me True
  3 &lt;TaskManager.filters.TaskFilter object at 0x7f87290dea90&gt; &lt;QuerySet []&gt; commented_tasks False
  </code></pre>
  
  <p>So I have two questions: First of all, why only first custom filter get queryset? Also, how can I make filter with three radio buttons which will be just return need queryset? </p>