android kotlin - Room with coroutines

MainActivity.kt


package com.example.coroutine

import android.os.Bundle
import android.text.method.ScrollingMovementMethod
import androidx.appcompat.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.coroutines.*
import java.util.*
import kotlin.random.Random


class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // get room database instance
        val db = RoomSingleton.getInstance(this)

        // make text view text scrollable
        textView.movementMethod = ScrollingMovementMethod()


        btnInsert.setOnClickListener {
            // generate a new student
            val student = Student(
                null,
                UUID.randomUUID().toString(),
                Random.nextInt(100)
            )

            // insert new student in room database
            GlobalScope.launch(Dispatchers.IO) {
                db.studentDao().insert(student)
            }
        }


        btnSelect.setOnClickListener {
            GlobalScope.launch(Dispatchers.IO) {
                // get student list from room database using background thread
                val list = db.studentDao().allStudents()
                    .sortedByDescending { it.id }

                // dispatcher that is confined to the Main
                // thread operating with UI objects
                withContext(Dispatchers.Main){
                    textView.text = "Students(${list.count()})..."

                    // loop through the students list
                    list.forEach {
                        textView.append("\n${it.id} : ${it.fullName} : ${it.result}")
                    }
                }
            }
        }


        btnClear.setOnClickListener {
            // dispatcher designed for offloading blocking
            // IO tasks to a shared pool of threads
            GlobalScope.launch(Dispatchers.IO) {
                // delete all students from room student table
                db.studentDao().clearStudents()
            }
        }
    }
}

activity_main.xml


<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#F5F5F5"
    tools:context=".MainActivity">

    <com.google.android.material.button.MaterialButton
        android:id="@+id/btnInsert"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:backgroundTint="#0048BA"
        android:text="Insert"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <com.google.android.material.button.MaterialButton
        android:id="@+id/btnSelect"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:backgroundTint="#008000"
        android:text="Select"
        app:layout_constraintBottom_toBottomOf="@+id/btnInsert"
        app:layout_constraintStart_toEndOf="@+id/btnInsert" />

    <com.google.android.material.button.MaterialButton
        android:id="@+id/btnClear"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:backgroundTint="#E52B50"
        android:text="Clear"
        app:layout_constraintBottom_toBottomOf="@+id/btnSelect"
        app:layout_constraintStart_toEndOf="@+id/btnSelect" />

    <com.google.android.material.textview.MaterialTextView
        android:id="@+id/textView"
        style="@style/TextAppearance.MaterialComponents.Subtitle1"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:textColor="#1B1811"
        android:textStyle="bold"
        android:padding="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/btnInsert"
        app:layout_constraintVertical_bias="1.0"
        tools:text="TextView" />

</androidx.constraintlayout.widget.ConstraintLayout>

RoomSingleton.kt


package com.example.coroutine

import androidx.room.Database
import androidx.room.Room
import androidx.room.RoomDatabase
import android.content.Context

@Database(entities = [Student::class], version = 1)
abstract class RoomSingleton : RoomDatabase() {
    abstract fun studentDao():StudentDao

    companion object {
        private var INSTANCE: RoomSingleton? = null
        fun getInstance(context: Context): RoomSingleton {
            if (INSTANCE == null) {
                INSTANCE = Room.databaseBuilder(
                    context,
                    RoomSingleton::class.java,
                    "roomdb")
                    .build()
            }
            return INSTANCE as RoomSingleton
        }
    }
}

RoomDao.kt


package com.example.coroutine

import androidx.room.Dao
import androidx.room.Insert
import androidx.room.OnConflictStrategy
import androidx.room.Query

@Dao
interface StudentDao{
    @Query("SELECT * FROM studentTbl")
    suspend fun allStudents():List<Student>

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    suspend fun insert(student:Student)

    @Query("DELETE FROM studentTbl")
    suspend fun clearStudents()
}

RoomEntity.kt


package com.example.coroutine

import androidx.room.ColumnInfo
import androidx.room.Entity
import androidx.room.PrimaryKey

@Entity(tableName = "studentTbl")
data class Student(
    @PrimaryKey
    var id:Long?,

    @ColumnInfo(name = "uuid")
    var fullName: String,

    @ColumnInfo(name = "result")
    var result:Int
)

build.gradle (app) [code to add]


apply plugin: 'kotlin-kapt'

dependencies {
    // kotlin coroutine
    implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.3.7'
    implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.3.7'

    // room database
    def room_version = "2.2.5"
    implementation "androidx.room:room-runtime:$room_version"
    implementation "androidx.room:room-ktx:$room_version"
    kapt "androidx.room:room-compiler:$room_version"
}