How To Learn Android Room Persistence Library Sqlite Mapper with Kotlin "Android Exmaple + Source Code'

In this tutorial, we will learn step by step using Android Room's persistent SQLite ORM mapper. As we have practiced in my last tutorial with GreenDAO which is a fast SQLite wrapper for ORM.

Google I / O 2017 has introduced the new database persistence library called Room as ORM like GreenDAO and ORMLite. There are 3 major components in Room.

• Database
• Entity
• DAO

Database: A database is a component that creates a database holder. Annotations define a list of entities, and the class content defines a list of data access objects (DAO) in the database. This is also the main access point for the underlying connection.

Entity: This component represents the class that stores the database row. For each entity, a database table is created to store items.

DAO: This component represents a class or interface as a Data Access Object (DAO). DAO is the main component of Room and is responsible for determining methods that access the database.

Ok, Let's integrate the Space library in one of the project examples with Kotlin reactively by RxJava2. The first thing to add relevant dependencies in the build.gradle file.

apply plugin: 'com.android.application' apply plugin: 'kotlin-android' apply plugin: 'kotlin-kapt' android { compileSdkVersion 26 buildToolsVersion "26.0.1" ........................ buildTypes { ................... } } dependencies { ................. compile "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version" compile 'android.arch.persistence.room:runtime:' + rootProject.archRoomVersion compile 'android.arch.persistence.room:rxjava2:' + rootProject.archRoomVersion kapt 'android.arch.persistence.room:compiler:' + rootProject.archRoomVersion compile 'io.reactivex.rxjava2:rxandroid:2.0.1' } repositories { mavenCentral() }

In project level of build.gradle file we need to add maven google path to download the dependency.

buildscript { ext.kotlin_version = '1.1.4-3' repositories { jcenter() } dependencies { classpath 'com.android.tools.build:gradle:2.3.3' classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version" // NOTE: Do not place your application dependencies here; they belong // in the individual module build.gradle files } } allprojects { repositories { jcenter() maven { url "https://maven.google.com" } // Do not forget to add this line } } task clean(type: Delete) { delete rootProject.buildDir } ext { buildToolsVersion = "26.0.0" supportLibVersion = "26.0.0" archRoomVersion = "1.0.0-alpha9" }

Now all setup is ready, let’s create the database entity.

@Entity(tableName = "friends") data class Friends ( @PrimaryKey var friend_id: String?, var name: String?, var email: String?) { }

Now let’s create a DAO class.

@Dao interface FriendsSource { @Query("SELECT * FROM friends") fun loadAllFriends(): Flowable<List<friends>> @Query("SELECT * FROM friends WHERE friend_id = :friend_id") fun loadFriend(friend_id: String?): Flowable<List<friends>> @Insert(onConflict = OnConflictStrategy.REPLACE) fun insertAll(products: MutableList<friends>) : Unit @Query("SELECT COUNT(*) from friends") fun countFriends(): Int }

Now create an instance of a database.

@Database(entities = arrayOf(Friends::class), version = 1) abstract class FriendsDatabase : RoomDatabase() { abstract fun friendsDao(): FriendsSource companion object { const val DATABASE_NAME = "friends-db" } }

Now let’s create the instance of the database to observing with Live data.

object DatabaseCreator { val isDatabaseCreated = MutableLiveData<boolean>() lateinit var database: FriendsDatabase private val mInitializing = AtomicBoolean(true) fun createDb(context: Context) { if (mInitializing.compareAndSet(true, false).not()) { return } isDatabaseCreated.value = false Completable.fromAction { database = Room.databaseBuilder(context, FriendsDatabase::class.java, FriendsDatabase.DATABASE_NAME).build() } .subscribeOn(Schedulers.computation()) .observeOn(AndroidSchedulers.mainThread()) .subscribe({ isDatabaseCreated.value = true }, {it.printStackTrace()}) } }

Let’s create an interface for what are the operations required in the project and implement those locally.

interface FriendsDataSource { fun getFriends(): Single<List<friends>> fun saveFriends(list: List<friends>) : Unit = Unit fun getCount(): Int }

Ok, Let’s implement those.

object FriendsLocalSource : FriendsDataSource { val friendsDao = DatabaseCreator.database.friendsDao() override fun getCount(): Int { return friendsDao.countFriends() } override fun getFriends(): Single<List<friends>> { return friendsDao.loadAllFriends() .firstOrError() .doOnSuccess { if (it.isEmpty()) throw Exception() } } override fun saveFriends(list: List<friends>) { friendsDao.insertAll(list.toMutableList()) } }

Please add database creator into MainApplication.

class MainApplication : Application() { override fun onCreate() { super.onCreate() DatabaseCreator.createDb(this) } }

Ok all done, We can call the insert operation to insert data into the table and get details from the database table.

fun saveFriendsIntoDb(list: List<friendsapimodel>){ var listFriends = ArrayList<friends>() for (FriendsApiModel in list) { var listUsers = FriendsApiModel!!.user; listUsers?.let { for (users in it) { listFriends.add(Friends(users.id, users.name, users.email)) } } } FriendsLocalSource.saveFriends(listFriends) }

disposable = FriendsLocalSource .getFriends() .subscribe { data, error -> this@FriendsLiveData.value = Pair(data, error)}

Wrapping Up:  This is the good implementation of Android Room with Kotlin. Room introduced in new Android Architecture component. But this is still in alpha, So it might change implementation.

You can get the full source code from Github.

Also Read :

• Full Source Code Android GAme Snow Skating With Admob Leaderboard - Free Download
• Universal v4.0 – Full Multi-Purpose Android App Source code Download Free
• Full Source Code Apps Mosque Finder Android to Admob reskinner Codecanyon
• Source Code Game Android Full Reskinner To ADMOB "Toby’s Adventures Beach "