在领域之间复制对象时需要迁移

Question

I'm trying to copy objects between two Realm databases. The first database's schema is version 0 and the second is version 1.

        let backupConfig = Realm.Configuration(
            path: "\(tmp)/ReadingLog.realm", // This Realm is version 0
            readOnly: true
        )

        let backupRealm = try! Realm(configuration: backupConfig)
        let defaultRealm = try! Realm() // My default Realm is version 1

        let books = backupRealm.objects(Book)

        try! defaultRealm.write {
            for book in books {
                defaultRealm.create(Book.self, value: book, update: true)
            }
        }

When I replace my current Realm database file with the old one the migration works perfectly. But if instead of replacing the files I try to copy objects between them I get "migration is required for object" etc.

I tried stating the paths, schemaVersions and migrationBlocks explicitly in every configuration, but it doesn't matter.

What am I doing wrong?

Thanks in advance,

Daniel

Answer 1

Ok, after a while going through the migration example I managed to sort it out.

I had to add my new schemaVersion (1) to the configuration of the old Realm database, which seems a little counter intuitive to me:

        let backupConfig = Realm.Configuration(
            path: "\(tmp)/ReadingLog.realm", // This file is version 0
            readOnly: true,
            schemaVersion: 1 // But I have to set this to version 1
        )

I thought schemaVersion should be this database's version, so Realm would know from what version to migrate, but actually it seems to be the new version I want it to migrate to .

Then I had to call migrateRealm(backupConfig) right after that. And then it worked!

So here's the working code:

        let backupConfig = Realm.Configuration(
            path: "\(tmp)/ReadingLog.realm",
            readOnly: true,
            schemaVersion: 1
        )
        migrateRealm(backupConfig)

        let backupRealm = try! Realm(configuration: backupConfig)
        let defaultRealm = try! Realm()

        let books = backupRealm.objects(Book)

        try! defaultRealm.write {

            for book in books {
                defaultRealm.create(Book.self, value: book, update: true)
            }
        }