Migrations

The rise of modern ORM frameworks that mapped database structures to database tables and entries meant that data became bound up to a degree with code structure. Database migrations are a way of keeping the schema that define your database version controlled in the same manner that the code that describes those structures are version controlled.

Database migration files are granular scripted files which describe your data, these are different depending on the tool you use. These migration files evaluate to SQL format migrations files. Indeed, you can write your migrations directly in SQL but this gives much more scope to introduce bugs and is more difficult.

Most popular languages and frameworks will have automated support for generating migration files but might require a small amount of manual changing. There are also third party migrations tools, such as Liquidbase or Flyaway that allow you to accomplish these tasks without being locked into a specific framework.

There are some migration tasks that are hard to reverse:

• Deleting columns
• Renaming columns
• Changing the datatype of columns that already contain data

It’s recommended when making changes to the features of your data to first introduce redundancy with extra features and then remove the old redundant features that no one is using anymore, allowing you to safely make changes.