Creating a new Migration

Warning

Never edit an already executed migration. Just create a new one

First of all, there are 2 types of migrations:

PRE

These migrations are the ones that are backwards compatible. For example, add a column or table, or solve an issue on a view.

POST

These migrations are used to cleanup the database once that all the servers code has been updated. These migrations are the ones that drop a column or table.

This is to take into account that all the servers can’t be updated at the same time (which would cause some downtime). For example, if we want to rename a column there should be a PRE and a POST migration:

• The PRE should create the new column and populate the value from the existing column

• The POST should delete the old column

The migration filename should follow the following template: YYYYMMDD_index_(pre or post)_(small description).sql. For example: 20160801_0_pre_add_foobar_column.sql. This isn’t optional because the migration system will fail if the migration doesn’t follow that format. The index is used to take into account that the same date can have more than one migration so the index identifies the order on which those file should be executed