Saving Data on Android

ALTER TABLE
 statement that adds a 
category
 column of 
type text with a default value of 
android
.
Open the 
QuizDatabase
 class and modify it like this
@Database(entities = [(Question::class)
, (Answer::
class
)], 
version = 3) //change version to version 3 
 
abstract
 
class
 
QuizDatabase
 : 
RoomDatabase
() {
Saving Data on Android
Chapter 10: Migrations with Room
raywenderlich.com
180

---

  
companion
 
object
{ 
    
val
 MIGRATION_1_TO_2 = Migration1To2() 
    
val
 MIGRATION_2_TO_3 = Migration2To3() 
//adds migration
 
  } 
  
abstract
 
fun
 
questionsDao
()
: QuestionDao 
}
The above code changes the database version to 3 and creates a reference to your 
new migration.
Now, open the 
QuizApplication.kt
 file and add the migration you just created to 
your database builder inside 
onCreate()
:
database = 
Room
.databaseBuilder(this, 
QuizDatabase
::
class
.
java
, 
"
question_database
") 
    .
addMigrations
(
QuizDatabase
.
MIGRATION_1_TO_2
, 
QuizDatabase
.
MIGRATION_2_TO_3
) 
    .
build
()
Build and run your app, then press 
START
:
Sweet! It looks like your migration works as expected.
Until now, the changes that you've made to your database schema have been really 
simple, since you only needed to add a new column to your tables.
But what happens if you need to modify a previously-created column?
Saving Data on Android
Chapter 10: Migrations with Room
raywenderlich.com
181

---

Well, it turns out that the 
ALTER TABLE
 statement is very limited; the only 
operations that you can perform with it are