Add the Room dependency:<\/strong> Make sure to sync your project after adding these dependencies.<\/p>\n\n\n\n Make sure to sync your project after adding these dependencies.<\/p>\n\n\n\n Entity<\/strong> represents a table in your database. Each field in the entity corresponds to a column in the table. Create a Kotlin file User.kt<\/strong>:<\/p>\n\n\n\n Here, User is an entity with three fields: id<\/strong>, name<\/strong>, and number<\/strong>. The id is the primary key, and it auto-generates when a new record is inserted.<\/p>\n\n\n\n The DAO<\/strong> is an interface that contains methods for accessing the database. Here, we’ll define the basic operations like inserting, querying, and deleting User objects.<\/p>\n\n\n\n Create a Kotlin file UserDao.kt<\/strong>:<\/strong><\/p>\n\n\n\n insert()<\/strong>, update()<\/strong>, and delete()<\/strong> are suspend functions because Room supports Kotlin coroutines for asynchronous operations.<\/p>\n\n\n\n getAllUsers()<\/strong> is a query method that returns a LiveData object, which automatically updates when the database changes.<\/p>\n\n\n\n Now, let’s create theRoomDatabase<\/strong> class. This is where Room will generate the database object.<\/p>\n\n\n\n Create a Kotlin file UserDatabase.kt<\/strong>:<\/strong><\/p>\n\n\n\n We define the database version and list of entities (User<\/strong> <\/strong>in this case).<\/p>\n\n\n\n getDatabase()<\/strong> <\/strong>is a singleton method that ensures only one instance of the database is created throughout the app.<\/p>\n\n\n\n The Repository<\/strong> acts as a mediator between the DAO and the UI. It abstracts access to the data and performs operations in a background thread using Kotlin coroutines.<\/p>\n\n\n\n Create a Kotlin fileUserRepository.kt<\/strong>:<\/strong><\/p>\n\n\n\n Here, we perform the database operations in a background thread using withContext(Dispatchers.IO)<\/strong>.<\/p>\n\n\n\n Now, let\u2019s create a ViewModel <\/strong>to manage UI-related data and interact with the repository.<\/p>\n\n\n\n Create a Kotlin file UserViewModel.kt<\/strong>:<\/strong><\/p>\n\n\n\n The ViewModel makes it easy to interact with the repository while keeping the UI lifecycle in mind.<\/p>\n\n\n\n Finally, let\u2019s use everything in an Activity. In your MainActivity.kt:<\/p>\n\n\n\n We observe allUsers<\/strong> LiveData <\/strong>to get real-time updates from the database.<\/p>\n\n\n\n We can add a new user by clicking the button, and the data will be inserted into the Room database.<\/p>\n\n\n\ndependencies {\n\n def room_version = \"2.6.1\"\n\n implementation \"androidx.room:room-runtime:$room_version\"\n\n \/\/ If this project uses any Kotlin source, use Kotlin Symbol Processing (KSP)\n \/\/ See KSP Quickstart to add KSP to your build\n ksp \"androidx.room:room-compiler:$room_version\"\n\n \/\/ If this project only uses Java source, use the Java annotationProcessor\n \/\/ No additional plugins are necessary\n annotationProcessor \"androidx.room:room-compiler:$room_version\"\n\n implementation \"androidx.lifecycle:lifecycle-viewmodel-ktx:$room_version\"\n\n implementation \"androidx.lifecycle:lifecycle-livedata-ktx:$room_version\"\n \n \/\/ To enable coroutine support\n implementation \"androidx.room:room-ktx:$room_version\"\n}<\/code><\/pre>\n\n\n\nStep 2: Define Entity<\/strong><\/h2>\n\n\n\n
Let’s create an entity called User.<\/p>\n\n\n\nimport androidx.room.Entity\nimport androidx.room.PrimaryKey\n\n@Entity(tableName = \"user_table\")\ndata class User(\n @PrimaryKey(autoGenerate = true) val id: Int = 0,\n val name: String,\n val number: Int\n)<\/code><\/pre>\n\n\n\nStep 3: Create a DAO (Data Access Object)<\/strong><\/h2>\n\n\n\n
import androidx.lifecycle.LiveData\nimport androidx.room.*\n\n@Dao\ninterface UserDao {\n\n @Insert\n suspend fun insert(user: User)\n\n @Update\n suspend fun update(user: User)\n\n @Delete\n suspend fun delete(user: User)\n\n @Query(\"SELECT * FROM user_table\")\n fun getAllUsers(): LiveData<List<User>>\n}<\/code><\/pre>\n\n\n\nStep 4: Create a Database<\/strong><\/h2>\n\n\n\n
import android.content.Context\nimport androidx.room.Database\nimport androidx.room.Room\nimport androidx.room.RoomDatabase\n\n@Database(entities = [User::class], version = 1, exportSchema = false)\nabstract class UserDatabase : RoomDatabase() {\n\n abstract fun userDao(): UserDao\n\n companion object {\n @Volatile\n private var INSTANCE: UserDatabase? = null\n\n fun getDatabase(context: Context): UserDatabase {\n return INSTANCE ?: synchronized(this) {\n val instance = Room.databaseBuilder(\n context.applicationContext,\n UserDatabase::class.java,\n \"user_database\"\n ).build()\n INSTANCE = instance\n instance\n }\n }\n }<\/code><\/pre>\n\n\n\nStep 5: Creating a Repository<\/strong><\/h2>\n\n\n\n
import android.app.Application\nimport androidx.lifecycle.LiveData\nimport kotlinx.coroutines.Dispatchers\nimport kotlinx.coroutines.withContext\n\nclass UserRepository(application: Application) {\n\n private val userDao: UserDao = UserDatabase.getDatabase(application).userDao()\n val allUsers: LiveData<List<User>> = userDao.getAllUsers()\n\n suspend fun insert(user: User) {\n withContext(Dispatchers.IO) {\n userDao.insert(user)\n }\n }\n\n suspend fun update(user: User) {\n withContext(Dispatchers.IO) {\n userDao.update(user)\n }\n }\n\n suspend fun delete(user: User) {\n withContext(Dispatchers.IO) {\n userDao.delete(user)\n }\n }\n}<\/code><\/pre>\n\n\n\nStep 6: ViewModel<\/strong><\/h2>\n\n\n\n
import android.app.Application\nimport androidx.lifecycle.AndroidViewModel\nimport androidx.lifecycle.LiveData\nimport kotlinx.coroutines.CoroutineScope\nimport kotlinx.coroutines.Dispatchers\nimport kotlinx.coroutines.launch\n\nclass UserViewModel(application: Application) : AndroidViewModel(application) {\n\n private val repository: UserRepository = UserRepository(application)\n val allUsers: LiveData<List<User>> = repository.allUsers\n\n fun insert(user: User) {\n CoroutineScope(Dispatchers.Main).launch {\n repository.insert(user)\n }\n }\n\n fun update(user: User) {\n CoroutineScope(Dispatchers.Main).launch {\n repository.update(user)\n }\n }\n\n fun delete(user: User) {\n CoroutineScope(Dispatchers.Main).launch {\n repository.delete(user)\n }\n }\n}<\/code><\/pre>\n\n\n\nStep 7: Using Room in Activity<\/strong><\/h2>\n\n\n\n
import android.os.Bundle\nimport androidx.activity.viewModels\nimport androidx.appcompat.app.AppCompatActivity\nimport androidx.lifecycle.Observer\nimport kotlinx.android.synthetic.main.activity_main.*\n\nclass MainActivity : AppCompatActivity() {\n\n private val userViewModel: UserViewModel by viewModels()\n\n override fun onCreate(savedInstanceState: Bundle?) {\n super.onCreate(savedInstanceState)\n setContentView(R.layout.activity_main)\n\n val adapter = UserAdapter()\n recyclerView.adapter = adapter\n\n userViewModel.allUsers.observe(this, Observer { users ->\n users?.let { adapter.submitList(it) }\n })\n\n \/\/ Adding a new user\n buttonAddUser.setOnClickListener {\n val user = User(name = \"John Doe\", age = 28)\n userViewModel.insert(user)\n }\n }\n}<\/code><\/pre>\n\n\n\n
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