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

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!

/*
* 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)
/*
* 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>
}
/*
* 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"))
}
}
/*
* 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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@aswin14887
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👍 ioThread{ } This is awesome. Thanks

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ghost commented Jun 9, 2018

In DataDatabase.kt why not to change

@Volatile private var INSTANCE: DataDatabase? = null

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

to

private var INSTANCE: DataDatabase? = null

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

The Java volatile keyword guarantees visibility of changes to variables across threads, that the value will be read from main memory either than CPU cache. This makes sense for public variables, like in this case:

public class SharedObject {

    public volatile int sharedParameter = 0;

}

in our case INSTANCE is private.
IMHO, @Synchonized method here gives the same result as @Volatile parameter + synchonized block but is much easier to understand

@vadymhimself
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You have a race condition when you insert into your database in another thread during its creation

@rezznov
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rezznov commented Sep 28, 2019

for those java developers witch ioThread is unknown for them, just run your code in background thread like this

AsyncTask.execute(() -> {
            roomInstance.dao().insert(new Model());
        });

@Jide-xy
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Jide-xy commented Mar 15, 2020

You have a race condition when you insert into your database in another thread during its creation

What's the solution for this?

@obinasBaba
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Embedded annotation can be used on a POJO or Entity only, not for a List. So, Room can not automatically flatten your list in this case.

@amberkira
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there is a bug: your initial data is not ready(perhaps IO takes long) when user call getXXX(). How to promise the data is absolutely inited when others need?

@tsuharesu
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tsuharesu commented Mar 9, 2021

@amberkira

there is a bug: your initial data is not ready(perhaps IO takes long) when user call getXXX(). How to promise the data is absolutely inited when others need?

https://stackoverflow.com/a/51139067/1981356

@amberkira
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@amberkira

there is a bug: your initial data is not ready(perhaps IO takes long) when user call getXXX(). How to promise the data is absolutely inited when others need?

https://stackoverflow.com/a/51139067/1981356

@tsuharesu

thx any way! but the answer is more about how to force onCreate Callback trigger ASAP which is not my concern. I've figure it out using Raw SQL sentences to prepopulate data

@wkwyatt
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wkwyatt commented May 1, 2021

@tsuharesu

@amberkira

there is a bug: your initial data is not ready(perhaps IO takes long) when user call getXXX(). How to promise the data is absolutely inited when others need?

https://stackoverflow.com/a/51139067/1981356

@tsuharesu

thx any way! but the answer is more about how to force onCreate Callback trigger ASAP which is not my concern. I've figure it out using Raw SQL sentences to prepopulate data

What was your answer? How did you figure it out with Raw SQL?

@gs-ts
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gs-ts commented Sep 24, 2021

any idea how to do this with Hilt?

@LMedez
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LMedez commented Feb 11, 2022

@gs-ts
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gs-ts commented Feb 12, 2022

thanks @LMedez !

@mrabhinv
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Thank you !! @florina-muntenescu

@ayitinya
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@tsuharesu

@amberkira

there is a bug: your initial data is not ready(perhaps IO takes long) when user call getXXX(). How to promise the data is absolutely inited when others need?

https://stackoverflow.com/a/51139067/1981356

@tsuharesu
thx any way! but the answer is more about how to force onCreate Callback trigger ASAP which is not my concern. I've figure it out using Raw SQL sentences to prepopulate data

What was your answer? How did you figure it out with Raw SQL?

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

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