title: Django: add a list filter option to filter related models under parent model
body: <p>I would like to request assistance in this matter</p>
  
  <p>I have the following models:</p>
  
  <pre><code>class Job(models.Model):
      Job_Position = models.CharField(max_length=30, null=True, unique=True)
  
  class Job_Posting(models.Model):
      fkey = models.ForeignKey("Job", verbose_name="Job Positions", unique=True)
  </code></pre>
  
  <p>and Admin:</p>
  
  <pre><code>class jobs(admin.TabularInline): 
      model = Job_Posting
      readonly_fields = [ 'fkey',]
      extra = 0
  
  class applicant(admin.ModelAdmin):
  
      model = Job
      list_display = ('Job_Position')
      list_filter = ['Job_Position']
      inlines = [jobs]
  </code></pre>
  
  <p>Is it possible to add a list filter option from inline? Something like this <code>list_filter = ['Job_Position', 'Job_Posting.fkey']</code> or for example, the current <code>list_filter</code> I have shows all items under <code>Job_Position</code>(selecting a <code>Job_Position</code> shows all record that have that position) and I want to add another option filtering all <code>Job_Position</code> that have that specific <code>Job_Posting.fkey</code> while giving me an option to see all the records</p>
  
  <p>Can you do this or it's not just possible? or if there are other options what would it be? Thanks in advance.</p>
  
  <p><strong>EDIT</strong></p>
  
  <p>I need something like <a href="https://docs.djangoproject.com/en/1.8/ref/contrib/admin/#django.contrib.admin.ModelAdmin.list_filter" rel="nofollow">this</a>, filtering all <code>Job</code> that has that <code>Job_Posting</code>, <code>fkey</code> in list_filter</p>