A migration that can be registered with MigrationManager. Note that the function does not need to migrate all the way to targetVersion, only to something higher than source._version. Usually a migration will only upgrade by 1.
MigrationManager
targetVersion
source._version
A migration that can be registered with
MigrationManager. Note that the function does not need to migrate all the way totargetVersion, only to something higher thansource._version. Usually a migration will only upgrade by 1.