title: filter query not working when searching on foreign key in django
body: <p>I've 2 classes in models.py - Users and authUser - 1st has app related info while 2nd has generic user info both are connected with a foreign key on username. </p>
  
  <p>I'm getting the user request info from 'request.user.username' and I'm trying to search in my users table to get app related info bsed on the logged in user. It's returning an empty queryset.</p>
  
  <p>I've tried - </p>
  
  <pre><code>print(Users.objects.filter(username__username = request.user.username))
  ----xx---
  print(Users.objects.filter(username = request.user.username))
  ----xx---
  print(Users.objects.filter(Q(username__username = request.user.username)))
  ----xx---
  print(Users.objects.get(username__username = request.user.username))
  </code></pre>
  
  <p>Even -</p>
  
  <pre><code>tmp = (Users.objects.all())
  for each in tmp:
      print(each.username)
      ----xx---
      print(each.username__username)
  </code></pre>
  
  <p>models.py</p>
  
  <pre><code>class Users(models.Model):
      userid = models.AutoField(db_column='UserID', primary_key=True)  # Field name made lowercase.
      username = models.ForeignKey('AuthUser', models.DO_NOTHING, db_column='Username', unique=True)  # Field name made lowercase.
      ownedfridges = models.TextField(db_column='OwnedFridges', blank=True, null=True)  # Field name made lowercase.
      friendedfridges = models.TextField(db_column='FriendedFridges', blank=True, null=True)  # Field name made lowercase.
      personalnotes = models.TextField(db_column='PersonalNotes', blank=True, null=True)  # Field name made lowercase.
      eff_bgn_ts = models.DateTimeField()
      eff_end_ts = models.DateTimeField()
  
      class Meta:
          managed = False
          db_table = 'Users'
  
  class AuthUser(models.Model):
      password = models.CharField(max_length=128)
      last_login = models.DateTimeField(blank=True, null=True)
      is_superuser = models.IntegerField()
      username = models.CharField(unique=True, max_length=150)
      first_name = models.CharField(max_length=30)
      last_name = models.CharField(max_length=150)
      email = models.CharField(max_length=254)
      is_staff = models.IntegerField()
      is_active = models.IntegerField()
      date_joined = models.DateTimeField()
  
      class Meta:
          managed = False
          db_table = 'auth_user'
  </code></pre>
  
  <p>views.py - </p>
  
  <pre><code>def home(request):
      current_user = request.user
      print(request.user)
      print(Users.objects.filter(username__username = request.user.username))
  
      print("---------------------------------------------------------")
  </code></pre>
  
  <p>I'm working with test1 user and the expected output is <code>Queryset&lt;[&lt;Users: Users object (1)&gt;]&gt;</code>
  whereas I'm getting <code>Queryset&lt;[]&gt;</code></p>