Develop Reference

(Android) When is the initial data stored in the Room database?

I'm currently trying to set up some initial data in the Room database.
As a result, the initial data setup was successful, but App Inspection confirmed that the data is saved only when getWorkoutList().
To explain in more detail, the initial data is not saved with the insert function alone, and the initial data is saved in the DB only when a function that calls the DB data called getWorkoutList() is executed from the ViewModel.
When the database is created in the view model, I expected the initial data to be saved only with the insert function. But it wasn't.
Why is the initial data not saved with only the insert function?
The following is the DB status in App inspection according to the function call.
1. When only insertWorkoutList(data) is executed
There is no DB and table creation, and no initial data is saved.
2. When only getWokroutList() is executed.
DB and table are created, but there is no data.
3. When both are executed.
Initial data is normally saved.
Code
Dao
#Dao
interface WorkoutListDao {
#Query("SELECT * FROM WorkoutList")
suspend fun getWorkoutList() : WorkoutList
#Insert
suspend fun insertWorkoutList(workoutList: WorkoutList)
}
WorkoutListDatabase
#Database(
entities = [WorkoutList::class],
version = 1
)
#TypeConverters(WorkoutListTypeConverter::class)
abstract class WorkoutListDatabase : RoomDatabase() {
abstract fun workoutListDao() : WorkoutListDao
companion object {
private var INSTANCE : WorkoutListDatabase? = null
#Synchronized
fun getDatabase(context: Context) : WorkoutListDatabase {
return INSTANCE ?: synchronized(this) {
val instance = Room.databaseBuilder(
context.applicationContext,
WorkoutListDatabase::class.java,
"workoutlist_db"
)
.addCallback(WorkoutListCallback(context))
.build()
INSTANCE = instance
instance
}
}
}
}
WorkoutListCallback
class WorkoutListCallback(private val context: Context) : RoomDatabase.Callback() {
override fun onCreate(db: SupportSQLiteDatabase) {
super.onCreate(db)
CoroutineScope(Dispatchers.IO).launch {
fillWithStartingWorkoutList(context)
}
}
private fun fillWithStartingWorkoutList(context: Context) {
val dao = WorkoutListDatabase.getDatabase(context).workoutListDao()
try {
val data = loadJsonData(context)
// dao.insertWorkoutList(data)
} catch (e: JSONException) {
e.printStackTrace()
}
}
private fun loadJsonData(context: Context) : WorkoutList {
val assetManager = context.assets
val inputStream = assetManager.open(WORKOUTLIST_JSON_FILE)
BufferedReader(inputStream.reader()).use { reader ->
val gson = Gson()
return gson.fromJson(reader, WorkoutList::class.java)
}
}
}
ViewModel
class WorkoutListViewModel(application: Application) : AndroidViewModel(application) {
private val workoutDao = WorkoutListDatabase.getDatabase(application).workoutListDao()
private val workoutListRepo = WorkoutListRepository(workoutDao)
fun setList(part : BodyPart) {
viewModelScope.launch(Dispatchers.IO) {
workoutListRepo.getWorkoutList()
}
}
}

The callback will only be called when the database is actually accessed NOT when an instance of the #Database annotated class is obtained.
As such the database is not created by:-
val dao = WorkoutListDatabase.getDatabase(context).workoutListDao()
but is created by
workoutListRepo.getWorkoutList()
That is the actual relatively resource hungry action of opening the database is left until it is definitely needed.
A get around could be to use :-
fun getDatabase(context: Context) : WorkoutListDatabase {
return INSTANCE ?: synchronized(this) {
val instance = Room.databaseBuilder(
context.applicationContext,
WorkoutListDatabase::class.java,
"workoutlist_db"
)
.addCallback(WorkoutListCallback(context))
.build()
INSTANCE = instance
instance.getOpenHelper().getWritableDatabase() //<<<<< FORCE OPEN
instance
}
}
This would then force an open of the database and if it does not actually exist then the overidden onCreate method will be invoked. However,this (I think) would be done on the main thread, which you do not want.
I would strongly suggest NOT using functions from the #Dao annotated class(es) especially if they have suspend as you then may have no control over when the threads will run.
Instead you should use the SupportSQLiteDatabase passed to the function, it has many methods e.g. you would likely use the insert method.
see ROOM database: insert static data before other CRUD operations for an example where the order was an issue. The example includes the conversion of the actions to utilise the intended SupportSQLiteDatabase methods.
You may notice that the example includes placing all the database changes into a single transaction, which is more efficient as instead of each individual action (insert/delete in the example) writing to disk, the entire transaction (all actions) are written to disk once.

android room always display closed in database inspector

I am trying to use Database Inspector in Android Studio.
When I run the app on the device, inspector always showing my application database
Is there anything I need to set before using it?
I am not using db.closed()
And here is my database module code
#Database(entities = [User::class], version = 1, exportSchema = false)
abstract class AppDatabase : RoomDatabase() {
abstract fun userDao(): UserDao
companion object {
//For singleton instantiation
#Volatile private var instance: AppDatabase?= null
fun getInstance(context: Context): AppDatabase {
return instance ?: synchronized(this) {
instance ?: buildDatabase(context).also { instance = it }
}
}
private fun buildDatabase(context: Context): AppDatabase {
return Room.databaseBuilder(context, AppDatabase::class.java, DATABASE_NAME)
.addCallback(
object : RoomDatabase.Callback() {
override fun onCreate(db: SupportSQLiteDatabase) {
super.onCreate(db)
}
}
).fallbackToDestructiveMigration()
.build()
}
}
}

Did you try some operation on DB e.g getlist
I have same issue when I am not in the page where DB is getting access.
Once I am in page, issue got resolved

Check the integrity of your database. You deleted an attribute, renamed a field, or deleted a model that is being referenced or imported in some class, when the room tries to load its data there is an integrity error and therefore it appears as closed.
Check your build and debug logs. I had the same problem and I solved it by the error logs and that was it.

I had the same issue, it is because in your actual session the connection is close... in other words you must execute one qwery on your app and the connection will be open.
Other option is create your create an instance on your main activity, this instance will open your database connection every time.

Populate data from csv to room database kotlin

I am trying to populate data from CSV to room database using kotlin in Android. I tried to convert the java code to Kotlin from this Populate Room database using csv file, but I am not able to access the Dao. Is there any better way to populate data from csv using Kotlin.
#Database(
entities = [MenuItem::class,
Order::class,
OrderItem::class,
Restaurant::class,
RestaurantRating::class,
User::class,
UserFavorite::class,
UserSearch::class],
version = 15,
exportSchema = false)
abstract class AppDatabase: RoomDatabase() {
abstract val orderDao: OrderDao
abstract val restaurantDao: RestaurantDao
abstract val userDao: UserDao
companion object{
#Volatile
private var INSTANCE: AppDatabase? = null
fun getInstance(context: Context): AppDatabase {
synchronized(this) {
var instance = INSTANCE
if (instance == null) {
instance = Room.databaseBuilder(
context.applicationContext,
AppDatabase::class.java,
"foodie_database.db"
)
.fallbackToDestructiveMigration()
.addCallback(object : RoomDatabase.Callback(){
override fun onCreate(db: SupportSQLiteDatabase) {
super.onCreate(db)
Executors.newSingleThreadExecutor().execute {
run {
}
}
}
})
.build()
INSTANCE = instance
}
return instance
}
}
}
}

From what I understand you are trying to pre-populate your database on first app startup. I didn't look into exactly how you can get access to the dao manually but the java example you pointed to I believe is using dagger dependency injection to get an instance of the dao.
How to overcome the circular dependency for a callback from Room.databaseBuilder using Dagger Hilt is wonderfully explained in a Code in flow video (link). I think this will give you enough information to figure out how to make the callback work.
Alternatively, and this is the one I prefer, you can use a database file instead of the csv file and use Room's inbuilt pre-population feature.
Just call .createFromAsset()orcreateFromFile() with Room.databaseBuilder()
Room.databaseBuilder(appContext, AppDatabase.class, "Sample.db")
.createFromAsset("myapp.db") //myapp.db in the assets folder
.build()
more from docs https://developer.android.com/training/data-storage/room/prepopulate#kotlin

Room databse loses data on restart application

According to documentation room instance from Room.databaseBuilder() should save data is persist. But still get lost. My Project have to database
First Database
#Database(entities = [FoodModel::class], version = 4, exportSchema = false)
abstract class FoodDatabase : RoomDatabase() {
abstract val foodDatabaseDao: FoodDatabaseDao
companion object {
#Volatile
private var INSTANCE: FoodDatabase? = null
fun getInstance(context: Context): FoodDatabase {
synchronized(this) {
var instance = INSTANCE
if (instance == null) {
instance = Room.databaseBuilder(
context.applicationContext,
FoodDatabase::class.java,
Constants.OVERVIEW_FOOD_DATABASE
)
.fallbackToDestructiveMigration()
.build()
INSTANCE = instance
}
return instance
}
}
}
}
Second Databse
#Database(entities = [MyFoodModel::class], version = 3, exportSchema = false)
abstract class MyFoodDatabase : RoomDatabase() {
abstract val myFoodDatabaseDao: MyFoodDatabaseDao
companion object {
#Volatile
private var INSTANCE: MyFoodDatabase? = null
fun getInstance(context: Context): MyFoodDatabase {
synchronized(this) {
var instance = INSTANCE
if (instance == null) {
instance = Room.databaseBuilder(
context.applicationContext,
MyFoodDatabase::class.java,
Constants.OVERVIEW_FOOD_DATABASE
)
.fallbackToDestructiveMigration()
.build()
INSTANCE = instance
}
return instance
}
}
}
}
Dao of first Database
#Dao
interface MyFoodDatabaseDao {
#Insert
fun insert(food: MyFoodModel)
#Query("SELECT * FROM MyFoodItems ORDER BY name DESC")
fun getAllFood(): LiveData<List<MyFoodModel>>
#Delete
fun deleteFood(foodModel: MyFoodModel)
}
Dao of Second database
#Dao
interface MyFoodDatabaseDao {
#Insert
fun insert(food: MyFoodModel)
#Query("SELECT * FROM MyFoodItems ORDER BY name DESC")
fun getAllFood(): LiveData<List<MyFoodModel>>
#Delete
fun deleteFood(foodModel: MyFoodModel)
}

An android application can have more than one database.
Here as I can see, You are providing same name [Constants.OVERVIEW_FOOD_DATABASE] to your both the databases [MyFoodDatabase, FoodDatabase]. So all values will be written in one database named as Constants.OVERVIEW_FOOD_DATABASE.
Please provide both the database different name and try again.
Edited
As you said, you are using two different instance of same databases and for every database instance, you are changing the database version but you are not migrating your database into that version. Instead you are using fallbackToDestructiveMigration() that does not crash database but clear the data when any existing version is found.
Please try below steps:
remove fallbackToDestructiveMigration() from both database instances.
in second instance add .addMigrations(MIGRATION_1_2) while creating
instance
val MIGRATION_1_2 = object : Migration(1, 2) {
override fun migrate(database: SupportSQLiteDatabase) {
// do nothing because you are not altering any table
}
}
in First instance add .addMigrations(MIGRATION_2_1) while creating instance
val MIGRATION_2_1 = object : Migration(2, 1) {
override fun migrate(database: SupportSQLiteDatabase) {
// do nothing because you are not altering any table
}
}
It will migrate you same database. In my case it is working. I hope it will work in your case too. :)
But it is better to use single database instance and include the list of entities associated with the database within the annotation.
Because room database instances are expensive.
https://developer.android.com/training/data-storage/room
Note: If your app runs in a single process, you should follow the singleton design pattern when instantiating an AppDatabase object. Each RoomDatabase instance is fairly expensive, and you rarely need access to multiple instances within a single process.
If your app runs in multiple processes, include enableMultiInstanceInvalidation() in your database builder invocation. That way, when you have an instance of AppDatabase in each process, you can invalidate the shared database file in one process, and this invalidation automatically propagates to the instances of AppDatabase within other processes.

I cannot execute more than one or two insertions in my Room database, for it will simply not persist the data after those

Whether it's an insert operation in table X or a delete one from table Y, the issue is that only one operation is being executed and for it to work again I need to re-run my app, making a new APK installation. That is, if I insert in table X and attempt to make another insert in table Y, although it will list in the app, it will not persist in the database.
I have confirmed it by running my application in debug mode and inspecting the database using the com.amitshekhar.android:debug-db:1.0.4. It is this weird, listing from the database while not being in the database. Then, when running the app one more time, these "ghost data" disappear.
I don't know what to show except for the operations code. The easiest one, a Student insertion:
fun onClickSaveStudentButton(view: View?) {
val studentName: String = mEdtStudentName?.text.toString()
val studentEntry = Student(null, studentName)
thread { mDb?.studentsDao()?.insert(studentEntry) }
finish()
}
Only one field for the name, and a thread executing the insertion. It sometimes will allow me to insert twice but after it, the same problem will happen. I thought it could be something with thread, so I installed Anko and made use of doAsync, but the problem continues.
This is the DAO function to insert:
#Insert
fun insert(data: Student)
What is going wrong here? Why's it only allowing me to insert once or twice?
The database class:
#Database(entities = [(Schedule::class), (Student::class)], version = 1)
abstract class AppDatabase : RoomDatabase() {
companion object {
#Volatile
private var sInstance: AppDatabase? = null
fun getInstance(context: Context): AppDatabase = sInstance ?: synchronized(this) {
sInstance ?: Room.databaseBuilder(
context,
AppDatabase::class.java,
Constants.DATABASE_NAME
).build().also {
sInstance = it
}
}
}
abstract fun scheduleDao(): ScheduleDao
abstract fun studentsDao(): StudentDao
}
And here, as example, Student model:
#Entity(tableName = "students")
class Student constructor(
#PrimaryKey(autoGenerate = true) var id: Int?,
#ColumnInfo(name = "name") var name: String?
)
Full code here.