Using RoomDatabase#Callback to pre-populate the database - https://medium.com/google-developers/7-pro-tips-for-room-fbadea4bfbd1

README.md

Pre-populate a Room database

To pre-populate a Room database, register a RoomDatabase#Callback in the database builder. Override the Callback#onCreate method to insert the data.

For details check out 7 Pro-tips for Room!

Data.kt

/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.observability.persistence

import android.arch.persistence.room.Entity
import android.arch.persistence.room.PrimaryKey

@Entity(tableName = "data")
data class Data(@PrimaryKey val id: String, val value: String)

DataDao.kt

/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.db

import android.arch.persistence.room.Dao
import android.arch.persistence.room.Insert
import android.arch.persistence.room.Query

@Dao
interface DataDao {

    @Insert
    fun insertData(data: List<Data>)

    @Query("SELECT * FROM Data")
    fun getData(): List<Data>
}

DataDatabase.kt

/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.db

import android.arch.persistence.db.SupportSQLiteDatabase
import android.arch.persistence.room.Database
import android.arch.persistence.room.Room
import android.arch.persistence.room.RoomDatabase
import android.content.Context

/**
 * The Room database that contains the Data table
 */
@Database(entities = arrayOf(Data::class), version = 1)
abstract class DataDatabase : RoomDatabase() {

    abstract fun dataDao(): DataDao

    companion object {

        @Volatile private var INSTANCE: DataDatabase? = null

        fun getInstance(context: Context): DataDatabase =
                INSTANCE ?: synchronized(this) {
                    INSTANCE ?: buildDatabase(context).also { INSTANCE = it }
                }

        private fun buildDatabase(context: Context) =
                Room.databaseBuilder(context.applicationContext,
                        DataDatabase::class.java, "Sample.db")
                        // prepopulate the database after onCreate was called
                        .addCallback(object : Callback() {
                            override fun onCreate(db: SupportSQLiteDatabase) {
                                super.onCreate(db)
                                // insert the data on the IO Thread
                                ioThread {
                                    getInstance(context).dataDao().insertData(PREPOPULATE_DATA)
                                }
                            }
                        })
                        .build()

        val PREPOPULATE_DATA = listOf(Data("1", "val"), Data("2", "val 2"))
    }
}

Executors.kt

/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.db

import java.util.concurrent.Executors

private val IO_EXECUTOR = Executors.newSingleThreadExecutor()

/**
 * Utility method to run blocks on a dedicated background thread, used for io/database work.
 */
fun ioThread(f : () -> Unit) {
    IO_EXECUTOR.execute(f)
}

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Ah yes, classic I've solved it without leaving the solution for others

The Classic must definitely go on! 2024 and still no sharing.

Ah yes, classic I've solved it without leaving the solution for others

The Classic must definitely go on! 2024 and still no sharing.

` @module
@Installin(SingletonComponent::class)
internal object DatabaseModule {

private const val DATABASE_NAME = "booking_db"

@Provides
@Singleton
fun providesBookingDatabase(
    @ApplicationContext context: Context,
): BookingDataBase = Room.databaseBuilder(
    context,
    BookingDataBase::class.java,
    DATABASE_NAME,
).addCallback(object : RoomDatabase.Callback() {
    override fun onCreate(db: SupportSQLiteDatabase) {
        db.execSQL("INSERT INTO HotelDBO (hotelName, hotelStars) VALUES ('The Grand Horizon', 3)")
        db.execSQL("INSERT INTO HotelDBO (hotelName, hotelStars) VALUES ('Azure Bliss Resort', 4)")
        db.execSQL("INSERT INTO HotelDBO (hotelName, hotelStars) VALUES ('Golden Sands Inn', 5)")
    }
}).build()

}`

it will work immediately and is ready to react reactively through the flow in the view model