Fix #15126: Better error message when passing invalid options to ModelForm.Meta.

django/forms/models.py

@@ -205,6 +205,21 @@ class ModelFormMetaclass(type):
         if 'media' not in attrs:
             new_class.media = media_property(new_class)
         opts = new_class._meta = ModelFormOptions(getattr(new_class, 'Meta', None))
+
+        # We check if a string was passed to `fields` or `exclude`,
+        # which is likely to be a mistake where the user typed ('foo') instead
+        # of ('foo',)
+        for opt in ['fields', 'exclude']:
+            value = getattr(opts, opt)
+            if isinstance(value, six.string_types):
+                msg = ("%(model)s.Meta.%(opt)s cannot be a string. "
+                       "Did you mean to type: ('%(value)s',)?" % {
+                           'model': new_class.__name__,
+                           'opt': opt,
+                           'value': value,
+                       })
+                raise TypeError(msg)
+
         if opts.model:
             # If a model is defined, extract form fields from it.
             fields = fields_for_model(opts.model, opts.fields,

tests/model_forms/tests.py

@@ -5,6 +5,7 @@ import os
 from decimal import Decimal
 
 from django import forms
+from django.core.exceptions import FieldError
 from django.core.files.uploadedfile import SimpleUploadedFile
 from django.core.validators import ValidationError
 from django.db import connection
@@ -228,6 +229,22 @@ class ModelFormBaseTest(TestCase):
         self.assertEqual(list(LimitFields.base_fields),
                          ['url'])
 
+    def test_limit_nonexistent_field(self):
+        expected_msg = 'Unknown field(s) (nonexistent) specified for Category'
+        with self.assertRaisesMessage(FieldError, expected_msg):
+            class InvalidCategoryForm(forms.ModelForm):
+                class Meta:
+                    model = Category
+                    fields = ['nonexistent']
+
+    def test_limit_fields_with_string(self):
+        expected_msg = "CategoryForm.Meta.fields cannot be a string. Did you mean to type: ('url',)?"
+        with self.assertRaisesMessage(TypeError, expected_msg):
+            class CategoryForm(forms.ModelForm):
+                class Meta:
+                    model = Category
+                    fields = ('url') # note the missing comma
+
     def test_exclude_fields(self):
         class ExcludeFields(forms.ModelForm):
             class Meta:
@@ -237,6 +254,23 @@ class ModelFormBaseTest(TestCase):
         self.assertEqual(list(ExcludeFields.base_fields),
                          ['name', 'slug'])
 
+    def test_exclude_nonexistent_field(self):
+        class ExcludeFields(forms.ModelForm):
+            class Meta:
+                model = Category
+                exclude = ['nonexistent']
+
+        self.assertEqual(list(ExcludeFields.base_fields),
+                         ['name', 'slug', 'url'])
+
+    def test_exclude_fields_with_string(self):
+        expected_msg = "CategoryForm.Meta.exclude cannot be a string. Did you mean to type: ('url',)?"
+        with self.assertRaisesMessage(TypeError, expected_msg):
+            class CategoryForm(forms.ModelForm):
+                class Meta:
+                    model = Category
+                    exclude = ('url') # note the missing comma
+
     def test_confused_form(self):
         class ConfusedForm(forms.ModelForm):
             """ Using 'fields' *and* 'exclude'. Not sure why you'd want to do