diff --git a/ponder/models.py b/ponder/models.py
index 2398aae..7cf2575 100644
--- a/ponder/models.py
+++ b/ponder/models.py
@@ -62,7 +62,9 @@ def email_categorizer(self):
 class Categorizer(models.Model):
 	name = models.CharField(unique=True, max_length=254)
 	initials = models.CharField(unique=True, max_length=3)
-	user = models.CharField(max_length=254)
+	
+	# The Django user this categorizer is related to. User is the Django user.
+	user = models.OneToOneField(User, to_field="username", db_column='user', on_delete=models.DO_NOTHING)
 
 	class Meta:
 		db_table = 'categorizers'
diff --git a/ponder/tests.py b/ponder/tests.py
index 6ae0ac7..afd8f7e 100644
--- a/ponder/tests.py
+++ b/ponder/tests.py
@@ -5,7 +5,8 @@
 from ponder.models import Categorization, Categorizer, Commit, Dataset, ProblemCategory, ProblemCause, ProblemSymptom, ProblemFix
 from django.contrib.auth.models import User
 from ponder.forms import CategorizationForm
-# Create your tests here.
+
+from django.db import IntegrityError
 
 class AddCategorizationFormTests(TestCase):
     '''
@@ -231,3 +232,53 @@ def test_category_text_not_null_and_func_fix_null(self):
             symptom_text='', symptom_description='',sha='0000000', data={"is_func_fix": False}, user='testUser')
         self.assertFalse(form.is_valid()) # The form should not be valid.
         self.assertEqual(form.errors["is_func_fix"], ["This field should be checked. An existing problem category indicates a bug fix."])
+
+class CategorizerTests(TestCase):
+    @classmethod
+    def setUpTestData(self):
+        # Create two new Django users.
+        self.user1 = User.objects.create_user(username='testUser1', password='testpassword')
+        self.user2 = User.objects.create_user(username='testUser2', password='testpassword')
+    
+    # Case when a new categorizer is being added when the given name already exists in the table.
+    def test_same_name(self):
+        # Make sure there are no other categorizers.
+        Categorizer.objects.all().delete()
+        
+        # Create a categorizer John Smith.
+        Categorizer.objects.create(name='John Smith', initials='JS', user=self.user1)
+        
+        # Second categorizer is inserted with the same name and different initials and username.
+        Categorizer.objects.create(name='John Smith', initials='AB', user=self.user2)
+        
+        # Both testUser1 and testUser2 with the name "John Smith" should be in the table because two categorziers can have the same name
+        self.assertTrue(Categorizer.objects.filter(user='testUser1').exists())
+        self.assertTrue(Categorizer.objects.filter(user='testUser2').exists())
+
+    # Case when a new categorizer is being added when the given initial already exists in the table.
+    def test_same_initials(self):
+        # Make sure there are no other categorizers.
+        Categorizer.objects.all().delete()
+        
+        # Create a categorizer John Smith.
+        Categorizer.objects.create(name='John Smith', initials='JS', user=self.user1)
+        
+        # Second categorizer is inserted with the same initials and different name and username.
+        # Exception here because the two users have the same initials.
+        self.assertRaises(IntegrityError, Categorizer.objects.create, name='Jane Scott', initials='JS', user=self.user2)
+        
+        # testUser1 with the initials "JS" should be in the table but not testUser2 because two categorziers can't have the same initials.
+        self.assertTrue(Categorizer.objects.filter(user='testUser1').exists())
+        self.assertFalse(Categorizer.objects.filter(user='testUser2').exists())
+
+    # Case when a new categorizer is being added when the given user already exists in the table
+    def test_same_user(self):
+        # Make sure there are no other categorizers.
+        Categorizer.objects.all().delete()
+        
+        # Create a categorizer John Smith.
+        Categorizer.objects.create(name='John Smith', initials='JS', user=self.user1)
+        
+        # The same user is inserted again with different name and initials.
+        # Expecting an exception because two categorizers can't be related to the same Django user.
+        self.assertRaises(IntegrityError, Categorizer.objects.create, name='Michelle Reed', initials='MR', user=self.user1)