Redmine provides @redmine_plugin_model@ generator. It's similar to @model@ generator by Rails but for Redmine plugin. It's useful to add a new model to Redmine plugin.

But Redmine doesn't provide @redmine_plugin_migration@ generator. It's similar to @migration@ generator by Rails but for Redmine plugin. It's useful to improve existing models in Redmine plugin.

We need to create a migration file for Redmine plugin by hand without @redmine_plugin_migration@.

The attached patch implements @redmine_plugin_migration@ generator. It only has the minimal features:

• Assign a new migration version.
• Just create a migration file that only has empty @change@ method.

The @migration@ generator by Rails has more features:

• Intelligent migration content generator. For example it can generate a migration content for creating a table from @create_TABLE_NAME@ migration name: https://github.com/rails/rails/blob/master/activerecord/lib/rails/generators/active_record/migration/migration_generator.rb#L39-L41
• Migration name validation: https://github.com/rails/rails/blob/master/activerecord/lib/rails/generators/active_record/migration/migration_generator.rb#L65-L69
• Accept more options. For example, attributes are accepted: https://github.com/rails/rails/blob/master/activerecord/lib/rails/generators/active_record/migration/migration_generator.rb#L8

I think that minimum implementation is a good starting point.

This implementation uses the framework for migration provided by Rails: https://github.com/rails/rails/blob/master/railties/lib/rails/generators/migration.rb