Courtesy: GitHub

Room Migration Sample

This is an API sample to showcase how to deal with database migrations using Room. From docs:

As you add and change features in your app, you need to modify your entity classes to reflect these changes. When a user updates to the latest version of your app, you don't want them to lose all of their existing data, especially if you can't recover the data from a remote server.

Room allows you to write Migration classes to preserve user data in this manner. Each Migration class specifies a startVersion and endVersion. At runtime, Room runs each Migration class's [migrate()]( method, using the correct order to migrate the database to a later version.



The sample app shows an editable user name, stored in the database.


The UI layer uses the Model-View-Presenter design pattern and works with a UserRepository class. The UserRepository has a reference to the local repository to get and save the data. It ensures that all of these operations are done off the UI thread. The UI layer classes are common for all flavors.


To showcase different implementations of the data layer product, flavors are used:

  • sqlite - Uses SQLiteOpenHelper and traditional SQLite interfaces. Database version is 1
  • room - Replaces implementation with Room and provides migrations. Database version is 2.
  • room2 - Adds a new column to the table and provides migration Database version is 3.
  • room3 - Changes the type of the table's primary key from int to String and provides migration. Database version is 4.


Use the Build Variants window in Android Studio to choose which version of the app you want to install, or alternatively choose one of the following tasks from the command line:

$ ./gradlew installSqliteDebug
$ ./gradlew installRoomDebug
$ ./gradlew installRoom2Debug
$ ./gradlew installRoom3Debug


The project uses both instrumentation tests that run on the device and local unit tests that run on your computer.

Device Tests

Database Tests

For the sqlite flavor the project is using the application database to test the functionality of LocalUserDataSource class. An in-memory database is used for room flavors UserDao and LocalUserDataSource tests, but still they are run on the device. An on-device database is used for the migration tests in all room flavors.

Local Unit Tests

Presenter Tests

The UserPresenter is tested using local unit tests with mocked Repository implementation.

Repository Tests

The UserRepository is tested using local unit tests with mocked UserDataSource and instant execution.


Copyright 2017 The Android Open Source Project, Inc.

Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

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versionName "1.0"



Main screen of the app. Displays a user name and allows the option to update the user name.