A great way to handle migrations in your iOS or Mac app. Provides a simple API to define blocks of code to run to migrate your app from earlier versions to its current version.

• Define what needs to be run to migrate your app to specific versions in a declarative manner.
• Sub-migrations enable you to run additional migrations without changing your app's version number.
• Use multiple migration managers to migrate parts of your app independently (optional).

MFMigrationManager requires version numbers to be specified in a style similar to Semantic Versioning (ex: 2.0.3) but places no limit on the actual number of components in the version number (2.0.3.9.6 would be a valid version number). MFMigrationManager also has its own syntax to refer to version numbers when it comes to sub-migrations (see below).

Using MFMigrationManager is a piece of cake. First, obtain a migration manager instance:

MFMigrationManager *manager = [MFMigrationManager migrationManager];

Then, specify code to run when migrating your app to specific versions:

[manager whenMigratingToVersion:@"1.1" run:^
{
	// Peform operations to migrate your app from version 1.0 to version 1.1
	[self migrateKeyedArchiveToCoreStorage];
}];

[manager whenMigratingToVersion:@"1.2.5" run:^
{
	// Perform operations to migrate your app from versions 1.1 and later to 1.2.5
	[self deleteCachedData];
}];

[manager whenMigratingToVersion:@"1.4" run:^
{
	// Perform operations to migrate your app from versions 1.2.5 and later to 1.4
	...
}];

This code should run each time your app launches so that the migration manager can do its job.

• Runs actions (if appropriate) as soon as -whenMigratingToVersion:run: is called.
• Runs all migrations from the version of the last app launch to the current version.
• Considers the current version to be the version defined in the info plist (CFBundleShortVersionString) unless specified manually.

As an example, given the migrations above, if the last version of the app that the user launched was version 1.1 and the user is now launching version 1.4, then MFMigrationManager would run migrations 1.2.5 and 1.4. Migration 1.1 would not run at that moment because it would already have been run when the app was launched as version 1.1.

Sometimes it can be useful to run migrations without changing your app's version number. Sub-migrations are meant for this:

[manager whenMigratingToVersion:@"1.1" run:^
{
	// Peform operations to migrate your app from version 1.0 to version 1.1
	[self migrateKeyedArchiveToCoreStorage];
}];

[manager whenMigratingToVersion:@"1.1-1" run:^
{
	// Perform operations to migrate your app from version 1.1 to sub-migration 1.1-1
}];

[manager whenMigratingToVersion:@"1.1-2" run:^
{
	// Perform operations to migrate your app from sub-migration 1.1-1 to sub-migration 1.1-2
}];

When encountering sub-migrations, MFMigrationManager runs all sub-migrations that it hasn't encountered yet for versions earlier than or equal to the current app version. In the example above, if the app version is 1.1, then all three migrations would run. Adding another migration with version 1.1-3 then starting the app again would run that migration, but not the other migrations because they have already been run.

If you'd rather use multiple migration managers to handle migrations in your app, you must obtain named migration managers. It could be a good idea to use the name of the class in which you're performing the migration as the migration manager's name, but that's up to you.

NSString *className = NSStringFromClass([self class]);
MFMigrationManager *manager = [MFMigrationManager migrationManagerWithName:className];

Afterwards, you can use your named migration managers totally independently. Define migrations for different version numbers, run blocks of code that affect different aspects of your app entirely, etc.

If MFMigrationManager's default behavior where CFBundleShortVersionString is considered as the current version doesn't fit your needs, you can also provide the current version manually:

NSString *version = [self obtainCurrentVersionNumberInSomeWay];
MFMigrationManager *manager = [MFMigrationManager migrationManagerWithCurrentVersion:version];

MFMigrationManager is available through CocoaPods, to install it simply add the following line to your Podfile:

pod "MFMigrationManager"

Michaël Fortin ([email protected])

MFMigrationManager is available under the MIT license. See the LICENSE file for more info.