Detect future database migrations

Related Projects GRDB
1

Hi,

Can a DatabaseMigrator detect (or report) that a database has migrated further than the migrator itself supports?
For example: A user with app version 1.1 sends the document (database) to a user with version 1.0. This new user should now get an error that the document is too new for his app to open.

Thanks in advance.

Kind regards,

Remco Poelstra

2

Hello @remcopoelstra,

This is quite an expectable use case, but it is not addressed in the documentation.

You can use this sample code:

extension DatabaseMigrator {
    /// Returns whether database contains unknown migration
    /// identifiers, which is likely the sign that the database
    /// has migrated further than the migrator itself supports.
    func hasBeenSuperseded(_ db: Database) throws -> Bool {
        let identifiers = try appliedIdentifiers(db)
        let migrations = try appliedMigrations(db)
        return identifiers != Set(migrations)
    }
}

try database.read { db in
    if try migrator.hasCompletedMigrations(db) == false {
        // document too old
    }
    if try migrator.hasBeenSuperseded(db) {
        // document too new
    }
}

Thank you for your report. The hasBeenSuperseded(_:) method is likely to be added to GRDB 5.

2 Likes
3

Hi,

Thanks! Looks like this extension works just fine (I had to change migrator to 'self' though).

4

Great :-) I have updated the sample code :+1: