Develop Reference

Migration in Room with an Android Array of Strings

I have a database in Android with Room from which I have deleted a column. I was doing the migration, and I saw that it was not as simple as doing a DROP of the deleted column.
Then I have seen that I have to take a series of steps, creating a provisional table that will later be the new table with the deleted column, but the problem is that this table contains a field that is a String Array that I don't know how to declare in SQL.
#Entity(tableName = "recipe_table")
data class RecipesDb(
#PrimaryKey
#ColumnInfo(name = "id")
val id: Long,
#ColumnInfo(name = "name")
val name: String,
#ColumnInfo(name = "category")
val category: List<String>,
#ColumnInfo(name = "isRecommended")
val isRecommended: Boolean,
#ColumnInfo(name = "images")
val images: List<String>,
#ColumnInfo(name = "ingredients")
val ingredients: List<String>,
#ColumnInfo(name = "date")
val date: Long,
#ColumnInfo(name = "time")
val time: Int,
#ColumnInfo(name = "difficult")
val difficult: String,
#ColumnInfo(name = "originalUrl")
val originalURL: String? = null,
#ColumnInfo(name = "author")
val author: String,
#ColumnInfo(name = "siteName")
val siteName: String
)
And now I have removed the ingredients column. I wanted to do something like this:
private val MIGRATION_3_2 = object : Migration(3,2) {
override fun migrate(database: SupportSQLiteDatabase) {
//Drop column isn't supported by SQLite, so the data must manually be moved
with(database) {
execSQL("CREATE TABLE Users_Backup (id INTEGER, name TEXT, PRIMARY KEY (id))")
execSQL("INSERT INTO Users_Backup SELECT id, name FROM Users")
execSQL("DROP TABLE Users")
execSQL("ALTER TABLE Users_Backup RENAME to Users")
}
}
}
But when I declare the new temporary table User_Backup, I have no idea how to specify that one of the fields is an Array. In the end I was able to do it with Room's AutoMigrations and creating an interface, but I would like to know how to do it this way as well.

The simple way is to compile the code (Ctrl+F9) with the changed #Entity annotated classes in the list of entities of the #Database annotation.
Then look at the generated java (visible via the Android View in Android Studio). There will be a class that is the same name as the #Database annotated class but suffixed with _Impl.
In this class there will be a method that is named createAllTables, This includes the SQL that room uses for creating the tables.
Just copy and paste the appropriate SQL and then change the table name, this will not only use the correct type but also apply the correct column constraints that Room expects.
I would suggest
Adding an execSQL("DROP TABLE IF EXISTS the_backup_table_name;") before you create a table (just in case it already exists)
And instead of using execSQL("DROP TABLE Users") to use execSQL("DROP TABLE IF EXISTS the_original_table_name")
Personally I always RENAME the table name of the original, then RENAME the new table and then finally DROP the renamed original.
I would use:-
private val MIGRATION_3_2 = object : Migration(3,2) {
override fun migrate(database: SupportSQLiteDatabase) {
//Drop column isn't supported by SQLite, so the data must manually be moved
with(database) {
execSQL("DROP TABLE IF EXISTS Users_Backup")
execSQL("CREATE TABLE IF NOT EXISTS ....) //<<<<< SEE NOTES BELOW, the SQL MUST BE CHANGED.
execSQL("INSERT INTO Users_Backup SELECT id, name FROM Users")
execSQL("ALTER TABLE Users RENAME TO Old_Users")
execSQL("ALTER TABLE Users_Backup RENAME to Users")
execSQL("DROP TABLE IF EXISTS Old_users")
}
}
}
note .... indicates that the SQL is copied from the generated java and that the table name is changed from Users to Users_Backup
The first line will drop the Uers_backup just in case it happens to exist, it's just a little less likely to fail under unusual circumstances.
Rather than dropping the Users table before the RENAME of the Users_Backup to Users. The 4th execSQL changes the name of the Users table, so should there be an issue with changing the Users_Backup table to be the Users table, then the original Uers table is available as Old_users.
When all has been complted then the original Users table, now named Old_Users is then dropped.
These are all just a little safer/secure.

SQLiteException: no such table: database-notes (code 1 SQLITE_ERROR)

I'm trying to migrate a new database version. The only thing changed is an added column. I always get the following error:
android.database.sqlite.SQLiteException: no such table: database-notes (code 1 SQLITE_ERROR): , while compiling: ALTER TABLE 'database-notes' ADD COLUMN image TEXT
I don't understand why I get this exception, because my table is named database-notes as written in the .build() call.
This is my database class:
#Database(
version = 2,
entities = [Note::class],
exportSchema = true)
abstract class AppDatabase : RoomDatabase() {
abstract fun noteDao(): NoteDAO
companion object {
fun build(context: Context) = Room.databaseBuilder(context, AppDatabase::class.java, "database-notes")
.addMigrations(MIGRATION_1_2).build()
}
}
val MIGRATION_1_2 = object : Migration(1, 2) {
override fun migrate(database: SupportSQLiteDatabase) {
database.execSQL("ALTER TABLE 'database-notes' ADD COLUMN image TEXT")
}
}
The database name was exactly the same in the previous version. I copied it to rule out typos.
What have I overlooked here? Thank you in advance!

because my table is named database-notes
It would appear not, due to the failure, and is probably a misunderstanding of the difference between the database name and table name(s).
A Database can have multiple tables. The database name is the name of the file itself (the container of the components such as tables, indexes, views and triggers).
In your code database-notes, as per the 3rd parameter to the Room.databaseBuilder is the name of the database (the file).
With Room the table names are derived from the classes that are both annotated with #Entity and provided, via the entities parameter of the #Database annotation. In your case the Note class.
The name of the table will be Note unless you use the tableName = parameter of the #Entity annotation to provide another name.
Example
If the following were your Note class :-
#Entity // No tableName parameter so the table name is the class name
data class Note(
#PrimaryKey
var noteId: Long? = null,
var noteText: String,
var image: String
)
Then the table name would be Note (the name of the class)
If the Note class were :-
#Entity(tableName = "notes") //<<<<< specifically names the table
data class Note(
#PrimaryKey
var noteId: Long? = null,
var noteText: String,
var image: String
)
The the table name would be notes (as specified by the tableName = parameter of the #Entity annotation).

Room prepopulated database not showing any data in table

I'm trying to have a prepopulated database with my Android app but I'm finding with the database inspector that the table is empty. I found it was working before I added a "favourite" column but now it doesn't work (also removing "favourites" still doesn't make it work, so I had changed other things too).
#Entity
#Parcelize
data class Quote (
#PrimaryKey(autoGenerate = true) val id: Int,
val quote: String,
val author: String,
val genre: String,
val favourite: Int
) : Parcelable
#Database(entities = [Quote::class], version = 10)
abstract class QuoteDatabase : RoomDatabase() {
abstract fun quoteDao(): QuoteDao
}
private lateinit var INSTANCE: QuoteDatabase
fun getDatabase(context: Context) : QuoteDatabase {
synchronized(QuoteDatabase::class.java) {
if (!::INSTANCE.isInitialized) {
INSTANCE = Room.databaseBuilder(context.applicationContext,
QuoteDatabase::class.java,
"quotes")
.createFromAsset("quotes.db")
.fallbackToDestructiveMigration()
.build()
}
return INSTANCE
}
}
// Exported Schema
"tableName": "Quote",
"createSql": "CREATE TABLE IF NOT EXISTS `${TABLE_NAME}` (`id` INTEGER PRIMARY KEY AUTOINCREMENT, `quote` TEXT NOT NULL, `author` TEXT NOT NULL, `genre` TEXT NOT NULL, `favourite` INTEGER NOT NULL)"
It looks like my schema is okay and I had even exported the schema from Room and it looks like it matches my current table schema. My file is also directly in "assets/quotes.db" (doesn't have any subfolders like "database"). The DB is being generated within the emulator from device file inspector. But database inspector is showing nothing. Even when I copy the file from the device and open it with DB Browser there's nothing in there. And of course, my prepopulated database has data in it.
What's going wrong?

How to Migrate Not Null table column into Null in Android Room database

I'm new to android room library. I need to migrate a Not Null column to Null,
But room migration only allow ADD or RENAME in ALTER table query. How do execute a column migration query?
#Entity(tableName = "vehicle_detail")
data class VehicleDetailsEntity(
#PrimaryKey(autoGenerate = true)
val vehicleClientId: Long = 0,
val vehicleId: String,
val updatedOn: Date,
val updatedBy: String
)
I need to change table structure into
#Entity(tableName = "vehicle_detail")
data class VehicleDetailsEntity(
#PrimaryKey(autoGenerate = true)
val vehicleClientId: Long = 0,
val vehicleId: String,
val updatedOn: Date?,
val updatedBy: String?
)
java.lang.IllegalStateException: Room cannot verify the data integrity. Looks like you've changed schema but forgot to update the version number. You can simply fix this by increasing the version number.

You need to run a migration since SQLite doesn't allow column constraint modification.
For that migration you need to create a new temp table and copy all your previous data to it, then delete the old table and rename the temp one to the needed table name.
If you have a scheme directory, you can find your exact creation SQL query which you should copy on your migration (I just figured it out from a scheme of mine and could not be 100% correct):
val MIGRATION_1_2: Migration = object : Migration(1, 2) {
override fun migrate(database: SupportSQLiteDatabase) {
// Create the new table
database.execSQL(
"CREATE TABLE IF NOT EXISTS VehicleDetailsEntityTmp (vehicleId TEXT NOT NULL, updatedOn TEXT, updatedBy TEXT,vehicleClientId INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL )"
)
// Copy the data
database.execSQL(
"INSERT INTO VehicleDetailsEntityTmp (vehicleId, updatedOn, updatedBy ,vehicleClientId) SELECT vehicleId, updatedOn, updatedBy ,vehicleClientId FROM VehicleDetailsEntity ")
// Remove the old table
database.execSQL("DROP TABLE VehicleDetailsEntity")
// Change the table name to the correct one
database.execSQL("ALTER TABLE VehicleDetailsEntityTmp RENAME TO VehicleDetailsEntity")
}
}

Android room migration add a list of enums

I'm saving
data class Settings(
val foo: Int
)
into my room database version 1.
Now I need to extend Settings to
data class Settings(
val foo: Int,
val bar: ArrayList<Baz>
)
where
enum class Baz {
A, B, C
}
so I need to do a migration to version 2.
I have type converters for bar. I'm currently trying something like
val MIGRATION_1_2: Migration = object : Migration(1, 2) {
override fun migrate(database: SupportSQLiteDatabase) {
database.execSQL("ALTER TABLE settings ADD COLUMN bar TEXT")
}
}
but this gives me an IllegalStateException: Migration didn't properly handle Settings... error.
And I'm stuck. So please help! How do I get that migration working??

Turns out it was my lack of SQLite skills that was in the way.
First of all, I needed to set a default value since my barwasn't allowed to be null. Second, ALTER TABLE is crazy limited and didn't allow me to set a default value in one line.
I ended up doing
val MIGRATION_1_2: Migration = object : Migration(1, 2) {
override fun migrate(database: SupportSQLiteDatabase) {
database.execSQL("CREATE TABLE settings_new (foo INTEGER NOT NULL, bar TEXT NOT NULL, PRIMARY KEY(foo))")
database.execSQL("INSERT INTO settings_new (foo, bar) SELECT foo, '[]' AS bar FROM settings")
database.execSQL("DROP TABLE settings")
database.execSQL("ALTER TABLE settings_new RENAME TO settings")
}
}
In other words
Create a new temporary table (settings_new)
Move old values into the new one. Notice that we set bar as an empty array as default.
Drop the original (settings) table
Rename the temporary to the old name (i.e. settings_new --> settings)

Try to change settings table name Settings and you pass only setting..
database.execSQL("ALTER TABLE Settings ADD COLUMN bar TEXT")
after add..
database = Room.databaseBuilder(context.getApplicationContext(),
UsersDatabase.class, "Sample.db")
.addMigrations(MIGRATION_1_2)
.build();
refer this ..
Room database migration if only new table is added