Android developer Dmitry Dogar talks on how to organize data persistence in Android using the new Room library. Topic inspired by Google Developer Group meetup.

1. Data persistence in
Android
with Room library
Dmitry Dogar, Android developer

2. World before Room

3. World before Room
• Boilerplate code

4. World before Room
• Boilerplate code

5. World before Room
•Difficult migrations

6. World before Room
•Difficult migrations

7. World before Room
• Hard to test

8. Solutions
3d-party ORM libraries over SQLite like:
• DBFlow
• Requery
• GreenDAO
• And so on, many of them!

9. Solutions
…OR even replacement for SQLite like

10. Google I/O 2017

11. Adding to project
Release notes: 1.0.0 - November 6, 2017

12. Room structure

13. Entity

14. Entity
Note: need getters & setters, not support for Lombok, AutoValue

15. Another Entity

16. Relation
Object references - not supported
From doc - Key takeaway: Room disallows object references between entity
classes. Instead, you must explicitly request the data that your app needs.

17. Relation

18. Embedding

19. Data types
Date - unknown type, requires converting

20. Data types
Should be added to database object

21. Database object

22. Database object

23. DAO
• QUERY
• INSERT
• UPDATE
• DELETE

24. DAO
- Need to write SQL queries, not typical for ORMs
- Retrofit style

25. DAO

26. DAO - code generation

27. DAO - code generation

28. DAO - Threading
• QUERY
• INSERT
• UPDATE
• DELETE
All Synchronous

29. DAO - Threading
• QUERY
• INSERT
• UPDATE
• DELETE
All Synchronous
Caused by: java.lang.IllegalStateException:
Cannot access database on the main thread since it may
potentially lock the UI for a long periods of time.

30. DAO - Threading
Quick, but not good fix

31. DAO - LiveData

32. DAO - RxJava

33. DAO - RxJava

34. DAO - RxJava

35. DAO - RxJava

36. DAO - Query, Joins
@Dao
public interface MyDao {
@Query("SELECT * FROM book "
+ "INNER JOIN loan ON loan.book_id = book.id "
+ "INNER JOIN user ON user.id = loan.user_id "
+ "WHERE user.name LIKE :userName")
public List<Book> findBooksBorrowedByNameSync(String userName);
}
From official documentation:

37. DAO - Query, Joins
Another way:

38. DAO - Query, Joins
Another way:

39. DAO - Query, Joins
Another way:

40. Testing

41. Testing

42. Testing

43. Testing

44. Testing
RxJava’s Flowable
Similar with LiveData

45. Testing
More real-life example UnitTest

46. Testing
More real-life example UnitTest

47. Migrations

48. Migrations

49. Migrations

50. Migrations
Update version

51. Migrations
Update version

52. Migrations
Provide migration

53. Migrations
Provide migration
Add it to db object

54. Migrations
Migrations execution

55. Migrations
Migrations execution
Shortest path

56. Migrations Testing

57. Migrations Testing
Setup
• Turn on schema export (as json file)
• In build.gradle: Set schema location to tests
• Export schema for annotation processor

58. Migrations Testing
@RunWith(AndroidJUnit4.class)
public class MigrationTest {
private static final String TEST_DB_NAME = “test_employee_db”;
@Rule
public MigrationTestHelper helper;
public MigrationTest() {
helper = new MigrationTestHelper(InstrumentationRegistry.getInstrumentation(),
EmployeesDatabase.class.getCanonicalName(),
new FrameworkSQLiteOpenHelperFactory());
}

59. Migrations Testing
@Test
public void migrate1To2() throws IOException {
SupportSQLiteDatabase db = helper.createDatabase(TEST_DB_NAME, 1);
insertEmployee(db); // need to insert with ContentValues SQLIte API
helper.runMigrationsAndValidate(TEST_DB_NAME, 2, true, MIGRATION_1_2);
And then build db object, get Data from DAO and write asserts

60. Summary
• Removes ugly boilerplate low level APIs code
• Google support
• Nice testing and RxJava2 support
• Use it if you need it

61. Links
• https://medium.com/@florina.muntenescu
Florina Muntenescu blogs
Aleksander Piotrowski, Talk at GDGDevFest 2017
Is there a room for Room?
• https://www.youtube.com/watch?v=BHiKSnOaoh4
• https://goo.gl/dNYY3S
Florina Muntenescu talk at realm.io
And official doc
• https://developer.android.com/training/data-storage/room/index.html

62. Thank you!