io.realm

Interface RealmMigration

public interface RealmMigration

The RealmMigration class is used to perform the migration of one Realm schema to another. The schema for a Realm is defined by all classes in a project that extend RealmObject or implement RealmModel, so any changes to these classes will require a migration.

To support migrations from any previous schemaVersion to the newest, the following pattern is recommended when writing a migration:

 
 public class CustomMigration implements RealmMigration {
   \@Override
   public long migrate(DynamicRealm realm, long oldVersion, long newVersion) {
     RealmSchema schema = realm.getSchema();

     if (oldVersion == 0) {
       // Migrate from v0 to v1
       oldVersion++;
     }

     if (oldVersion == 1) {
       // Migrate from v1 to v2
       oldVersion++;
     }

     if (oldVersion < newVersion) {
         throw new IllegalStateException(String.format("Migration missing from v%d to v%d", oldVersion, newVersion));
     }
   }
 }
 
 

During development when RealmObject classes can change frequently, it is possible to use Realm.deleteRealm(RealmConfiguration). This will delete the database file and eliminate the need for any migrations.

See Also:

RealmConfiguration.Builder.schemaVersion(long), RealmConfiguration.Builder.migration(RealmMigration), RealmConfiguration.Builder.deleteRealmIfMigrationNeeded()

Method Summary

Modifier and Type	Method and Description
void	migrate(DynamicRealm realm, long oldVersion, long newVersion) This method will be called if a migration is needed.

Method Detail

migrate

void migrate(DynamicRealm realm,
             long oldVersion,
             long newVersion)

This method will be called if a migration is needed. The entire method is wrapped in a write transaction so it is possible to create, update or delete any existing objects without wrapping it in your own transaction.

Parameters:

realm - the Realm schema on which to perform the migration.

oldVersion - the schema version of the Realm at the start of the migration.

newVersion - the schema version of the Realm after executing the migration.