Kotlin中Room的简单使用

增加引用

  // kotlin
  implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
  implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.0.0'
  implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.0.0'
  // Room
  implementation "androidx.room:room-runtime:2.2.5"
  kapt "androidx.room:room-compiler:2.2.5"

apply

apply plugin: 'kotlin-kapt'

导出数据库建表语句

android {
// ...
    defaultConfig {
        //指定room.schemaLocation生成的文件路径  处理Room 警告 Schema export Error
        javaCompileOptions {
            annotationProcessorOptions {
                arguments = [
                        "room.schemaLocation"  : "$projectDir/schemas".toString(),
                        "room.incremental"     : "true",
                        "room.expandProjection": "true"]
            }
        }
    }
// ...
}

实体类

@Entity(tableName = "worker")
class Worker() : Parcelable {
    @PrimaryKey(autoGenerate = true)
    @ColumnInfo(name = "_id")
    var id: Long = 0
    lateinit var name: String

    constructor(parcel: Parcel) : this() {
        id = parcel.readLong()
        name = parcel.readString().toString()
    }

    override fun writeToParcel(parcel: Parcel, flags: Int) {
        parcel.writeLong(id)
        parcel.writeString(name)
    }

    override fun describeContents(): Int {
        return 0
  }

    companion object CREATOR : Parcelable.Creator<Worker> {
        override fun createFromParcel(parcel: Parcel): Worker {
            return Worker(parcel)
        }

        override fun newArray(size: Int): Array<Worker?> {
            return arrayOfNulls(size)
        }
    }
}

Dao

@Dao 
interface WorkerDao {
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    fun insertWorker(worker: Worker)

    @Query("DELETE FROM worker WHERE name=:name")
    fun deleteWorker(name: String)

    @Query("SELECT * FROM worker")
    fun queryAllWorkers(): List<Worker>
}

创建数据库

@Database(entities = [Worker::class], version = 1)
abstract class KotDatabase : RoomDatabase() {
    abstract fun getWorkerDao(): WorkerDao

    companion object {
        @Volatile
        private var INSTANCE: KotDatabase? = null
        fun getInstance(context: Context): KotDatabase =
                INSTANCE ?: synchronized(this) {
                   INSTANCE ?: buildDatabase(context).also { INSTANCE = it }
                }    
        private fun buildDatabase(context: Context) =
                Room.databaseBuilder(context.applicationContext, KotDatabase::class.java, "kot.db")
                        .build()
    }
}

增

GlobalScope.launch(Dispatchers.IO) {
  val worker = Worker()
  worker.name = "李华"
  KotDatabase.getInstance(applicationContext).getWorkerDao().insertWorker(worker)
  withContext(Dispatchers.Main) {
      Toast.makeText(applicationContext, "插入完成", Toast.LENGTH_SHORT).show()
} }

删

GlobalScope.launch(Dispatchers.IO) {
  KotDatabase.getInstance(applicationContext).getWorkerDao().deleteWorker("李华")
  withContext(Dispatchers.Main) {
      Toast.makeText(applicationContext, "删除完成", Toast.LENGTH_SHORT).show()
} }

查

GlobalScope.launch(Dispatchers.IO) {
  val workers = KotDatabase.getInstance(applicationContext).getWorkerDao().queryAllWorkers()
  withContext(Dispatchers.Main) {
      Toast.makeText(applicationContext, "查询完成", Toast.LENGTH_SHORT).show()
} }

升级数据库

实体类，新增age字段

@Entity(tableName = "worker")
class Worker() : Parcelable {
    @PrimaryKey(autoGenerate = true)
    @ColumnInfo(name = "_id")
    var id: Long = 0
    var age: Int = 0
    lateinit var name: String

    constructor(parcel: Parcel) : this() {
        id = parcel.readLong()
        age = parcel.readInt()
        name = parcel.readString().toString()
    }

    override fun writeToParcel(parcel: Parcel, flags: Int) {
        parcel.writeLong(id)
        parcel.writeInt(age)
        parcel.writeString(name)
    }

    override fun describeContents(): Int {
        return 0
  }

    override fun toString(): String {
        return "Worker(id=$id, age=$age, name='$name')"
  }

    companion object CREATOR : Parcelable.Creator<Worker> {
        override fun createFromParcel(parcel: Parcel): Worker {
            return Worker(parcel)
        }

        override fun newArray(size: Int): Array<Worker?> {
            return arrayOfNulls(size)
        }
    }
}

数据库

@Database(entities = [Worker::class], version = 2)
abstract class KotDatabase : RoomDatabase() {
    abstract fun getWorkerDao(): WorkerDao

    companion object {
        @Volatile
        private var INSTANCE: KotDatabase? = null
        fun getInstance(context: Context): KotDatabase =
                INSTANCE ?: synchronized(this) {
                    INSTANCE ?: buildDatabase(context).also { INSTANCE = it }
                }    
        private fun buildDatabase(context: Context) =
                Room.databaseBuilder(context.applicationContext, KotDatabase::class.java, "kot.db")
                        .addMigrations(migration1to2)
                        .build()

        private val migration1to2: Migration = object : Migration(1, 2) {
            override fun migrate(database: SupportSQLiteDatabase) {
                database.execSQL("ALTER TABLE worker ADD COLUMN 'age' INTEGER NOT NULL")
            }
        }
    }
}

多版本迁移

@Database(entities = [Worker::class], version = 3)
abstract class KotDatabase : RoomDatabase() {
    abstract fun getWorkerDao(): WorkerDao

    companion object {
        @Volatile
        private var INSTANCE: KotDatabase? = null
        fun getInstance(context: Context): KotDatabase =
                INSTANCE ?: synchronized(this) {
                    INSTANCE ?: buildDatabase(context).also { INSTANCE = it }
                }    
        private fun buildDatabase(context: Context) =
                Room.databaseBuilder(context.applicationContext, KotDatabase::class.java, "kot.db")
                        .addMigrations(migration1to2, migration2to3)
                        .build()

        private val migration1to2: Migration = object : Migration(1, 2) {
            override fun migrate(database: SupportSQLiteDatabase) {
                database.execSQL("ALTER TABLE worker ADD COLUMN 'age' INTEGER NOT NULL")
            }
        }

        private val migration2to3: Migration = object : Migration(2, 3) {
            override fun migrate(database: SupportSQLiteDatabase) {
                // 新建表
                database.execSQL("CREATE TABLE IF NOT EXISTS worker_new (`_id` INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, `age` INTEGER NOT NULL, `name` TEXT NOT NULL)")
                // 复制表
                database.execSQL("INSERT INTO worker_new (`_id`, `age`, `name`) SELECT `_id`, `age`, `name` FROM worker")
                // 删除表
                database.execSQL("DROP TABLE worker")
                // 重命名表
                database.execSQL("ALTER TABLE worker_new RENAME TO worker")
            }
        }
    }
}