1、引包

    implementation 'androidx.room:room-runtime:2.2.5'
    implementation 'androidx.room:room-common:2.2.5'

2、编写bean

/**
 * user 实体类定义
 *  indices = [Index(value = ["name"], unique = true)]  = name 唯一约束
 */
@Entity(indices = [Index(value = ["name"], unique = true)])
class User() {
    //自增长主键
    @PrimaryKey(autoGenerate = true)
    var autoId: Int = 0

    @ColumnInfo(name = "name")
    var name: String? = null
    var nickName: String? = null
    var age: Int? = null
}

3、Dao类

/**
 * user 对应的dao类
 */
@Dao
public interface UserDao {
    /**
     * 插入user对象
     * @param user Array<out User> 一个user或者多个user
     */
    @Insert(onConflict = OnConflictStrategy.REPLACE)//有了就替换
    fun insertAll(vararg user: User)

    /**
     * 删除user对象
     */
    @Delete
    fun delete(vararg user: User)

    @Update
    fun updates(vararg user: User)

    /**
     * 查找所有
     * @return List<User>
     */
    @Query("select * from user")
    fun loadAll(): List<User>

    /**
     * 根据用户名查找用户
     * @param name String
     * @return User?
     */
    @Query("select * from user where name = :name ")
    fun findByName(name: String): User
}

4、数据库抽象类

/**
 * 定义了数据库中数据表  版本号
 */
@Database(entities = [User::class], version = 2)
public abstract class AppDataBase : RoomDatabase() {
    abstract fun userDao(): UserDao
}

5、数据库管理工具

object AppDataBaseHelper {
    private val databseName: String = "mydatabase"
    private var dataBase: AppDataBase? = null
        private get() {
            return field
        }
        private set

    public fun getDB(): AppDataBase {
        if (null == dataBase) {
            throw RuntimeException("请先init database")
        }
        return dataBase!!
    }

    fun initDb(application: Application) {
        dataBase = Room.databaseBuilder(
            application,
            AppDataBase::class.java,
            databseName)
            //.addMigrations() 添加升级规则
            .allowMainThreadQueries()
            .build()
    }

    //升级规则
    val MIGRATION_1_2: Migration = object : Migration(1, 2) {
        override fun migrate(database: SupportSQLiteDatabase) {
            database.execSQL(
                "CREATE TABLE `Fruit` (`id` INTEGER, "
                        + "`name` TEXT, PRIMARY KEY(`id`))"
            )
        }
    }

    val MIGRATION_2_3: Migration = object : Migration(2, 3) {
        override fun migrate(database: SupportSQLiteDatabase) {
            database.execSQL(
                ("ALTER TABLE Book "
                        + " ADD COLUMN pub_year INTEGER")
            )
        }
    }
}

6、测试用

class RoomActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_room)
        var u = User()
        u.name = "张三测试2"
        u.age = 19
        u.nickName = "abu"
        GlobalScope.launch(Dispatchers.IO) {
            AppDataBaseHelper.initDb(application)
            AppDataBaseHelper.getDB().userDao().insertAll(u)
            val userList = AppDataBaseHelper.getDB().userDao().loadAll()
            withContext(Dispatchers.Main) {
                userList.forEach {
                    println(Gson().toJson(it))
                }
            }
        }
    }
}