Saving Data on Android

QuizAplication.kt
 and modify your database builder inside 
onCreate()
:
database = Room.databaseBuilder(
this
, QuizDatabase::
class
.
java
, 
"question_database")
 
    .addMigrations(QuizDatabase.MIGRATION_1_TO_2) 
//Only this 
line changes
 
    .build()
addMigrations()
 accepts one or more migration objects. Room will use these 
migrations to bring the database to the latest version.
Build and run your app and press 
START
 to verify that your migration works 
properly:
Sweet! It looks like your app works now.
Saving Data on Android
Chapter 10: Migrations with Room
raywenderlich.com
179

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Next, imagine that you want to sort your questions not only by difficulty but also by 
a category, such as 
iOS
 or 
Android
. This way, you can expand the functionality of 
your app to display Android questions to Android developers and iOS questions to 
iOS developers.
Expanding the functionality of your app to support categories requires some changes 
in your database:
• A new property inside your question entity called 
category
 of type String.
• A new migration that goes from database version 2 to 3 and handles the new 
schema change.
• Adding the new migration to your database builder.
Start by opening the 
Question.kt
 file and adding a new 
category
 property to your 
class:
@Entity(tableName = "question", indices = 
[Index("question_id")
]) 
data
 
class
 
Question
( 
  
@PrimaryKey(autoGenerate = true)
 
  
@ColumnInfo(name = "question_id")
 
  
var
 questionId: 
Int
, 
  
val
 text: String, 
  
val
 difficulty: 
Int
 = 
0
, 
  
val
 category: String = 
"android"
 
//Only this line changes
 
)
Now, create a new class under the migrations package and name it 
Migration2To3
. 
Replace everything inside with the following:
class
 
Migration2To3
 : 
Migration
(
2
, 
3
) { 
  
override
 
fun
 
migrate
(database: SupportSQLiteDatabase)
 { 
    database.execSQL(
"ALTER TABLE question ADD COLUMN category 
TEXT NOT NULL DEFAULT 'android'"
) 
  } 
}
Here, you're creating a new 
Migration
 object that goes from database version 2 to 3. 
The query executes an