A database upgrade must add bookmarks without losing learning progress. How would you ship it?

Answer

A clean installation only proves the new schema can be created. Existing users need a path from their stored schema to the new one that preserves the meaning of their data.

Suppose LessonProgress already has an id primary key and a completion column. Adding a non-null bookmark flag requires a value for old rows.

Example

This migration fragment assumes version 4 introduces isBookmarked:

Copy codeval MIGRATION_3_4 = object : Migration(3, 4) {
    override fun migrate(db: SupportSQLiteDatabase) {
        db.execSQL(
            "ALTER TABLE LessonProgress " +
                "ADD COLUMN isBookmarked INTEGER NOT NULL DEFAULT 0"
        )
    }
}

Declare a matching database default in the entity, such as @ColumnInfo(defaultValue = "0"), update the database version, and register the migration. This snippet assumes a Room configuration using the corresponding support SQLite APIs.

How to verify

Use exported schemas and MigrationTestHelper to create an older database, insert completed and incomplete lessons, migrate, and verify both schema and values. Test upgrade paths for users who skip releases, plus a fresh installation.

Follow-up to practise

Why not enable destructive fallback? Dropping and recreating tables can erase the only copy of learning progress. It may suit disposable caches, but it must be an explicit data-loss decision rather than a way to silence migration failures.

Reference

Android Developers: Room migrations