Migrations.md

DB Migrations made easy!

Whenever you modify the DB schema you need to increment the DB version through within the @Database class it corresponds to. Also you need to add a Migration to the configuration or define the migration via /assets/migrations/{DatabaseName}/{versionName.sql}.

You can specify a migration to run when database is first created by using version 0!

Note any provided subclass such as AlterTableMigration, UpdateTableMigration, and IndexMigration should only override onPreMigrate() and call super.onPreMigrate() so it's instantiated properly.

Note All Migration must only have a public default constructor.

Migration Classes

The base class, BaseMigration provides a very simple class to execute your migration:

@Migration(version = 2, database = AppDatabase.class)
public class Migration1 extends BaseMigration {

    @Override
    public void migrate(DatabaseWrapper database) {
      List<SomeClass> list = SQLite.select()
          .from(SomeClass.class)
          .queryList(database); // must pass in wrapper in order to prevent recursive calls to DB.
    }
}

Adding Columns

Here is an example of adding a column to the DB:

Say we have the original example class:

@Table
public class TestModel extends BaseModel {

    @Column
    @PrimaryKey
    String name;

    @Column
    int randomNumber;
}

Now we want to add a column to this table. We have two ways:

• Put the SQL statement

  ALTER TABLE TestModel ADD COLUMN timestamp INTEGER; in a {dbVersion.sql} file in the assets directory. If we need to add any other column, we have to add more lines.

• Through a Migration:

@Migration(version = 2, database = AppDatabase.class)
public class Migration1 extends AlterTableMigration<TestModel> {

    @Override
    public void onPreMigrate() {
      // Simple ALTER TABLE migration wraps the statements into a nice builder notation
      addColumn(Long.class, "timestamp");
    }
}

Updating Columns

@Migration(version = 2, database = AppDatabase.class)
public class Migration1 extends UpdateTableMigration<TestModel> {

    @Override
    public void onPreMigrate() {
      // UPDATE TestModel SET deviceType = "phablet" WHERE screenSize > 5.7 AND screenSize < 7;
      set(TestModel_Table.deviceType.is("phablet"))
        .where(TestModel_Table.screenSize.greaterThan(5.7), TestModel_Table.screenSize.lessThan(7));
    }
}