Rails 3 - 将大块数据从旧数据库模式移动到新数据库模式

I was working on an app until some months ago. After that, it was decided that the app should go through a major overhaul. This involved changing a lot of the database schema. To accomplish the objective, we opted to work on another branch. When we had to make a migration, we did it not troubling ourselves to include code that dealt with current data available in the database so that it became compatible with the new db schema. This development went this way for some months. Now, we need to take all the data from the old database schema and migrate it into the new database schema.I was working on an app until some months ago.