Allow exact field duplicates, and error if there's a name conflict.

typedmodels/models.py

@@ -111,7 +111,19 @@ def do_related_class(self, other, cls):
                     remote_field = field.remote_field
                     if isinstance(remote_field.model, TypedModel) and remote_field.model.base_class:
                         remote_field.limit_choices_to['type__in'] = remote_field.model._typedmodels_subtypes
-                field.contribute_to_class(base_class, field_name)
+
+                # Check if a field with this name has already been added to class
+                try:
+                    duplicate_field = base_class._meta.get_field(field_name)
+                    # Check if the field being added is _exactly_ the same as the field
+                    # that already exists.
+                    if duplicate_field.deconstruct()[1:] != field.deconstruct()[1:]:
+                        raise ValueError("Can't add field '%s' from '%s' to '%s', field already exists.",
+                            field_name, classname, base_class.__name__)
+                    # Otherwise, the field already exists on the base class. Don't add it.
+                except FieldDoesNotExist:
+                    field.contribute_to_class(base_class, field_name)
+
                 classdict.pop(field_name)
             base_class._meta.fields_from_subclasses.update(declared_fields)
 

typedmodels/test_models.py

@@ -109,3 +109,16 @@ class Child1(Parent):
 
 class Child2(Parent):
     pass
+
+
+class Employee(TypedModel):
+    pass
+
+
+class Developer(Employee):
+    name = models.CharField(max_length=255, null=True)
+
+
+class Manager(Employee):
+    # Adds the _exact_ same field as Developer. Shouldn't error.
+    name = models.CharField(max_length=255, null=True)

typedmodels/tests.py

@@ -14,7 +14,7 @@
 
 from .models import TypedModelManager
 from .test_models import AngryBigCat, Animal, BigCat, Canine, Feline, Parrot, AbstractVegetable, Vegetable, \
-    Fruit, UniqueIdentifier, Child2
+    Fruit, UniqueIdentifier, Child2, Employee
 
 
 @pytest.fixture
@@ -308,3 +308,15 @@ def test_explicit_recast_with_string_on_untyped_instance():
     animal.recast('typedmodels.feline')
     assert animal.type == 'typedmodels.feline'
     assert type(animal) is Feline
+
+
+def test_same_field_name_in_two_subclasses():
+    with pytest.raises(ValueError):
+        class Tester1(Employee):
+            name = models.CharField(max_length=255, blank=True, null=True)
+    with pytest.raises(ValueError):
+        class Tester2(Employee):
+            name = models.CharField(max_length=254, null=True)
+    with pytest.raises(ValueError):
+        class Tester3(Employee):
+            name = models.IntegerField(null=True)