Database Migrations

Overview

Since the first release, Preside has supported automatic schema synchronisation with your Preside Object data model. It has also supported core Preside system data migrations for a long time. Now, as of 10.18.0, Preside also supplies a straightforward framework for application and extension developers to supply their own one time data migration scripts.

Implementation

The implementation involves developers supplying a convention-based coldbox handler with either run() or runAsync() methods that perform any database data migrations necessary with normal Preside/Coldbox code. The convention is /handlers/dbmigrations/yourmigrationid.cfc.

Any migrations are run in name order. It is recommended therefore that you name your migration handlers in a sensible order friendly way. For example, using the date of handler creation as a prefix.

Example

/**
 * Handler at /handlers/dbmigrations/2022-05-25_defaultEventModes.cfc
 *
 */
component {

	private void function run() {
		getPresideObject( "my_object" ).updateData(
			  filter = "my_new_flag is null"
			, data = { my_new_flag = true }
		);
	}

}

Synchronous vs Asynchronous running

When you implement a run() method, your logic will run during application startup and application startup will not be complete until the migration completes. This is important for critical migrations where the application's data must be updated in order for correct operation of the application.

If your migration is not essential to the running of the application, you may wish to implement a runAsync() method instead. These migrations will be run in a background thread approximately 1 minute after application startup. Great for slow, non-essential migrations.

Both methods operate and are called in exactly the same way. Neither method receives any arguments other than core coldbox event, rc and prc.