mssql-django Index Issue

This project was created to reproduce a problem with indexes created by mssql-django version 1.1.

Steps to reproduce:

1. Create a model with a char field that allows NULL values. Make and apply migrations.

• migration: 0001 in the widgets app.
• reference commit 4a261e16 in this project.

2. Alter the char field so that it no longer allows NULL values. Make and apply migrations.

• migration: 0002 in the widgets app.

• reference commit 732704a7 in this projejct.

• This migration created in this step creates the problematic index.

  BEGIN TRANSACTION
  --
  -- Alter field url on widget
  --
  DROP INDEX [widgets_widget_url_98f0535d] ON [widgets_widget];
  ALTER TABLE [widgets_widget] ADD DEFAULT '' FOR [url];
  UPDATE [widgets_widget] SET [url] = '' WHERE [url] IS NULL;
  ALTER TABLE [widgets_widget] ALTER COLUMN [url] nvarchar(255) NOT NULL;
  CREATE INDEX [widgets_widget_url_98f0535d] ON [widgets_widget] ([url]); -- <--- Problematic index
  SELECT d.name FROM sys.default_constraints d INNER JOIN sys.tables t ON d.parent_object_id = t.object_id INNER JOIN sys.columns c ON d.parent_object_id = c.object_id AND d.parent_column_id = c.column_id INNER JOIN sys.schemas s ON t.schema_id = s.schema_id WHERE t.name = 'widgets_widget' AND c.name = 'url';
  ALTER TABLE [widgets_widget] DROP CONSTRAINT [url];
  COMMIT;

3. Change the char field to a text field. Make and attempt to apply migrations.

• migration: 0003 in the widgets app.
• reference commit 3070df23 in this project.
• This migration will fail because the index widgets_widget_url_98f0535d was not dropped first.

This problem does not occur with mssql-django version 1.0. Migration 0002 generates the following SQL:

--
-- Alter field url on widget
--
ALTER TABLE [widgets_widget] ADD DEFAULT '' FOR [url];
UPDATE [widgets_widget] SET [url] = '' WHERE [url] IS NULL;
ALTER TABLE [widgets_widget] ALTER COLUMN [url] nvarchar(255) NOT NULL;
SELECT d.name FROM sys.default_constraints d INNER JOIN sys.tables t ON d.parent_object_id = t.object_id INNER JOIN sys.columns c ON d.parent_object_id = c.object_id AND d.parent_column_id = c.column_id INNER JOIN sys.schemas s ON t.schema_id = s.schema_id WHERE t.name = 'widgets_widget' AND c.name = 'url';
ALTER TABLE [widgets_widget] DROP CONSTRAINT [url];