just FYI I was recently bitten by a problem in a database migration. Rails database migrations don't run in a transaction if the underlying database does not support transactional schema changes (which mysql does not). 

The problem I had was that I was adding a new edition type, and inserting new records into the editions table with a type which was not defined. This triggered an error:

```
An ActionView::Template::Error occurred in organisations#show:

  The single-table inheritance mechanism failed to locate the subclass: 'DocumentCollection'. This error is raised because the column 'type' is reserved for storing the class in case of inheritance. Please rename this column if you didn't intend it to be used for storing the inheritance class or overwrite Edition.inheritance_column to use another column for that information.
  activerecord (3.2.14) lib/active_record/inheritance.rb:143:in `rescue in find_sti_class'
```

I'm not sure if this migration would trigger this error, given that the existing class is not using STI, however, it may well do.

So it might be worth explicitly wrapping the two `execute` statements here in a transaction.