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io.realm

Interface RealmMigration

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  • io.realm
  • Method Summary
  • Method Detail
  • migrate

io.realm

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 io.realm.RealmObject or implement io.realm.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(Locale.US, "Migration missing from v%d to v%d", oldVersion, newVersion));
    }
  }
}

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

Tip

See also:

Method Summary

Modifier and Type
Method and Description
public void
migrate (
DynamicRealm realm,
long oldVersion,
long newVersion
)

This method will be called if a migration is needed.

Method Detail

migrate

public 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.

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RealmModel