Use of room database in kotlin

room Configuration of database

1room Preparation before using the database

1 stay App Under the build.gradle.kt Add room Database dependency

 //room Database dependency 
    implementation ("androidx.room:room-runtime:2.3.0")
    annotationProcessor ("androidx.room:room-compiler:2.3.0")
    implementation ("androidx.room:room-ktx:2.3.0")
    kapt ("androidx.room:room-compiler:2.3.0")

    // The dependence of synergy 
    implementation ("org.jetbrains.kotlinx:kotlinx-coroutines-android:1.1.1")

    // introduce lifecycle Dependence 
    implementation("androidx.lifecycle:lifecycle-runtime-ktx:2.3.1")

2 Prepare entity classes for storing data in the database , If the table name is not specified , The default is the name of the entity class

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

@Entity
class User(var username: String, var password: String) {
    
        @PrimaryKey(autoGenerate = true)
        var id: Long = 0

        override fun toString(): String {
    
                return "id by ：${id} The user is called ：$username: The password for $password"
        }
}

3 Prepare to interact with the database dao Interface

import androidx.room.*
import com.hikvision.mykotlintest.database.entity.User

@Dao
interface UserDao {
    
        @Insert
        fun insertUser(user: User):Long

        @Update
        fun updateUser(user:User):Int

        @Query("select * from User")
        fun queryAllUser():List<User>

        @Delete()
        fun deleteUser(user: User):Int

        @Query("delete from User where username=:name")
        fun deleteByName(name:String):Int

        @Query("select id,username,password from User where username=:name")
        fun queryUserByName(name:String):User

        // To verify whether the password is correct, you need to make a query according to the password and user name 
        @Query("select id,username,password from User where username=:name and password=:password")
        fun queryUserByName(name:String,password:String):User

}

4 Database creation , And when modifying and adding tables later , Update the database as follows

import android.content.Context
import androidx.room.Database
import androidx.room.Room
import androidx.room.RoomDatabase
import androidx.room.migration.Migration
import androidx.sqlite.db.SupportSQLiteDatabase
import com.hikvision.mykotlintest.database.dao.FriendDao
import com.hikvision.mykotlintest.database.dao.MessageDao

import com.hikvision.mykotlintest.database.dao.UserDao
import com.hikvision.mykotlintest.database.entity.Address
import com.hikvision.mykotlintest.database.entity.Friend
import com.hikvision.mykotlintest.database.entity.User
import com.hikvision.mykotlintest.entity.Messages

@Database(version = 4, entities = [User::class,Friend::class,Messages::class], exportSchema = false)
abstract class AppDatabase : RoomDatabase() {
    
        abstract fun userDao(): UserDao

        //abstract fun addressDao(): AddressDao

        abstract fun friendDao():FriendDao

        abstract fun messageDao():MessageDao

        companion object {
    
                private var instance: AppDatabase? = null

                // When adding a new table, you only need to add Migrate rewrite , Then rewrite the method ,migrate,
              /* private var Migrate_1_2=object : Migration(1,2){ override fun migrate(database: SupportSQLiteDatabase) { database.execSQL("create table Address (id integer primary key autoincrement not null, name text not null, image text not null)" ) } }*/
                // Add a new one friend surface , Used in address Interface Click friendList when , Show friend What is the specific information of 
               private var Migrate_2_3=object : Migration(2,3){
    
                        override fun migrate(database: SupportSQLiteDatabase) {
    
                                database.execSQL("create table Friend(id integer primary key autoincrement not null, name text not null,gender integer not null,nickname text not null," +
                                                "wechatNum text not null,address text not null,avatar integer not null)" )
                        }

                }

                // Added a message table . It stores messages with everyone , Distinguish according to the user's name and category , If it is 0. Description is the message sent , If it is 1, Is the received message 
               private var Migrate_3_4=object : Migration(3,4){
    
                        override fun migrate(database: SupportSQLiteDatabase) {
    
                                database.execSQL("create table Messages(id integer primary key autoincrement not null, name text not null,message text not null,type integer not null)" )
                        }

                }

                //kotlin Normal double check lock writing method 
                fun getDatabaseSingleton2(context: Context): AppDatabase =
                        instance ?: synchronized(AppDatabase::class.java) {
    
                                instance ?: Room.databaseBuilder(
                                        context.applicationContext,
                                        AppDatabase::class.java,
                                        "app__lang_database"
                                ).addMigrations( Migrate_2_3, Migrate_3_4).allowMainThreadQueries().build().also {
    
                                        instance = it
                                }
                        }


                // Return a database instance , The single interest model , If you haven't created , Just create a new one named app_lang_database The database of 
                @Synchronized
                fun getDatabase(context: Context): AppDatabase {
    
                        instance?.let {
    
                                return it
                        }
                        return Room.databaseBuilder(
                                context.applicationContext,
                                AppDatabase::class.java,
                                "app__lang_database"
                        ).allowMainThreadQueries()
                                .build().apply {
    
                                        instance = this
                                }
                }

                // Write a double check simple interest model 
                fun getDatabaseSingleton(context: Context): AppDatabase {
    
                        if (instance == null) {
    
                                synchronized(AppDatabase::class.java) {
    
                                        if (instance == null) {
    
                                                instance = Room.databaseBuilder(
                                                        context.applicationContext,
                                                        AppDatabase::class.java,
                                                        "app__lang_database"
                                                ).allowMainThreadQueries().build()
                                                        .apply {
     instance = this }
                                        }
                                }
                        }
                        return instance!!
                }
        }
}

2room Use of database

1 Install the plug-in to check whether the database is successfully created Database Navigator

Database Navigator After adding the plug-in successfully ,DBManager It will appear in Android Studio Top left corner of

2 Introduce the use of database into logic code

1 Login interface layout

import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.text.method.HideReturnsTransformationMethod
import android.text.method.PasswordTransformationMethod
import android.view.MotionEvent
import android.view.View
import android.widget.Button
import android.widget.EditText
import android.widget.ImageView

import android.widget.TextView
import androidx.annotation.CallSuper
import com.hikvision.mykotlintest.database.dao.UserDao
import com.hikvision.mykotlintest.database.database.AppDatabase
import com.hikvision.mykotlintest.recycle.NewsMainActivity
import com.hikvision.mykotlintest.util.KeyboardSetting
import com.hikvision.mykotlintest.util.KeyboardUtils


class MainActivity : AppCompatActivity() {
    
        var count = 0;
        var showPassword = false
        //private lateinit var password:EditText
        lateinit var name:EditText
        
        lateinit var btnGoToRegister:Button
        // Create dao Interface 
        private lateinit var userDao:UserDao
        
        override fun onCreate(savedInstanceState: Bundle?) {
    
                super.onCreate(savedInstanceState)
                setContentView(R.layout.activity_main)
                name =findViewById<EditText>(R.id.textOfName)
                name.setText(intent?.getStringExtra("username"))
                // Instantiation dao Interface 
                userDao=AppDatabase.getDatabaseSingleton2(this).userDao()
                // Here you need to recover the user name 
                btnGoToRegister=findViewById(R.id.goToRegister)
                btnGoToRegister.setOnClickListener {
    
                        startActivityForResult(Intent(this,RegisterActivity::class.java),1)
                }

        }
        // Bind the listening event for the current confirm login button 
        fun sureBtn1(view: View) {
    
                var name =findViewById<TextView>(R.id.textOfName)
                var password = findViewById<EditText>(R.id.textOfPassWord)
                var message = findViewById<TextView>(R.id.mess)
                var forgetPW=findViewById<TextView>(R.id.forgetPW)
                /* *  Resources that require change , I hope to change from a locked state to an unlocked state , Then you can click the eye button at the back , Make the password display  * */
                var lockOpen = getDrawable(R.drawable.ic_baseline_lock_open_24)

                var text = name.text.toString()
                var text1 =password.text.toString()
                // Find out whether the current user exists from the database , Determine whether the user name and password are correct 
                if (userDao.queryUserByName(text,text1)!=null) {
    
                  
                        var intent = Intent(this@MainActivity, ThanksActivity::class.java)
                        intent.putExtra("name", text)
                        // Pass parameters to another interface 
                        startActivity(intent)
                        
                } else {
    
                        count++
                        if (count < 10) {
    
                                message.setText(" Wrong password or user name , Do you have ${10 - count} Second chance ")
                                password.setText("")
                                forgetPW.setText(" Forget the password ？ Click to retrieve ")
                        } else {
    
                                message.setText(" Locked , Please be there. 10 Try again in minutes ")
                        }
                }
        }

}

Once you execute this activity, The database will be created , At this point, the database will be created successfully , The table will also automatically create a table according to the field attributes of the entity class , Then according to the installed plug-ins DB Browser, You can check the information in the table you created .