Ticket #12203: 12203-m2m-w-through-modeladmin-fields-option1.diff

django/contrib/admin/validation.py

@@ -149 +149 @@
             validate_inline(inline, cls, model)
 
 def validate_inline(cls, parent, parent_model):
-    
+
     # model is already verified to exist and be a Model
     if cls.fk_name: # default value is None
         f = get_field(cls, cls.model, cls.model._meta, 'fk_name', cls.fk_name)
@@ -200 +200 @@
             raise ImproperlyConfigured('Both fieldsets and fields are specified in %s.' % cls.__name__)
         if len(cls.fields) > len(set(cls.fields)):
             raise ImproperlyConfigured('There are duplicate field(s) in %s.fields' % cls.__name__)
+        for idx, field in enumerate(cls.fields):
+            f = get_field(cls, model, opts, 'fields', field)
+            if isinstance(f, models.ManyToManyField) and f.rel.through:
+                raise ImproperlyConfigured("'fields' option can't include a ManyToManyField field that uses the 'through' option. Problem is in %s.fields, '%s' field." % (cls.__name__, field))
 
     # fieldsets
     if cls.fieldsets: # default value is None

tests/regressiontests/admin_validation/models.py

@@ -26 +26 @@
     e = models.CharField(max_length=1)
 
 
+class Author(models.Model):
+    name = models.CharField(max_length=100)
+
+
+class Book(models.Model):
+    name = models.CharField(max_length=100)
+    authors = models.ManyToManyField(Author, through='AuthorsBooks')
+
+
+class AuthorsBooks(models.Model):
+    author = models.ForeignKey(Author)
+    book = models.ForeignKey(Book)
+
 
 __test__ = {'API_TESTS':"""
 
@@ -95 +108 @@
 
 >>> validate_inline(TwoAlbumFKAndAnEInline, None, Album)
 
+# Regression test for #12203 - Fail more gracefully when a M2M field that
+# specifies the 'through' option is included in the 'fields' ModelAdmin option.
+
+>>> class BookAdmin(admin.ModelAdmin):
+...     fields = ['authors']
+
+>>> validate(BookAdmin, Book)
+Traceback (most recent call last):
+    ...
+ImproperlyConfigured: 'fields' option can't include a ManyToManyField field that uses the 'through' option. Problem is in BookAdmin.fields, 'authors' field.
 """}