Getting past db data when realm migration

Question

I have used realm database(iOS and Android both). It worked well still now and migration. When migration, I could add table and additional columns in updated schema. By the way, I have no idea whether I'm capable of extracting previous table data and move to new schema table. Please let me know about this.

Answer 1

Just to confirm, you've successfully managed to perform a schema migration with Realm on both the iOS and Android versions of your app, but your question is whether you can extract data from a table in an older schema version and move it to a new table in your latest schema version. Is this correct?

If this is correct, then yes. At the time of performing a migration, you can run a loop inside your MigrationBlock block/ RealmMigration object to manually copy the data from an older table to a newly created one.

Examples of this logic can be found in the sample code of both the iOS and Java repositories on Realm's GitHub account.

Unfortunately, once a migration has completed on a Realm file and the previous table has been deleted, then it's not possible to back-track and extract the data at a later time.

Answer 2

You could do something like this:

RealmSchema schema = realm.getSchema();

schema.get("OldTableName").renameField("OldFieldName", "NewFieldName");

schema.rename("OldTableName", "NewTableName");