Saving Data on Android

QuizApplication.kt
 file and add your new migration to the database 
builder:
database = Room.databaseBuilder(
this
, QuizDatabase::
class
.
java
, 
"question_database")
 
    .addMigrations( 
      QuizDatabase.MIGRATION_1_TO_2,  
      QuizDatabase.MIGRATION_2_TO_3, 
      QuizDatabase.MIGRATION_3_TO_4,  
      QuizDatabase.MIGRATION_1_TO_4 
    ).build()
Cool! You now have a migration that goes directly from database version 1 to 4. If 
you build the app, the migration won't execute since your app is already on database 
version 4, but you can now be sure that all your users on database version 1 will 
properly migrate to the new version when they update the app.
Saving Data on Android
Chapter 10: Migrations with Room
raywenderlich.com
185

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Key points
• Simply put, a database migration or schema migration is the process of moving 
your data from one database schema to another.
• SQLite handles database migrations by specifying a version number for each 
database schema that you create.
• Room provides an abstraction layer on top of the traditional SQLite migration 
methods with 
Migration
.
•
Migration(startVersion, endVersion)
 is the base class for a database 
migration. It can move between 
any
 two migrations defined by the 
startVersion
 
and 
endVersion
 parameters.
•
fallbackToDestructiveMigration()
 tells Room to destructively recreate tables 
if you haven't specified a migration.