Room

Room是Google为了简化旧版的SQLite操作专门提供的
1.拥有了SQLite的所有操作功能
2.使用简单（类似于Retrofit），通过注解的方式实现相关功能。编译时自动生成实现类impl
3.LiveData，LifeCycle，Paging天然融合支持

导入

...plugins { id 'com.android.application' id 'kotlin-android' id 'kotlin-android-extensions' id 'kotlin-kapt'}dependencies { //room数据库 implementation "androidx.room:room-runtime:2.2.5" kapt "androidx.room:room-compiler:2.2.5" // Kotlin 使用 kapt implementation "androidx.room:room-ktx:2.2.5"//Coroutines support for Room 协程操作库 //lifecycle implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0' implementation 'androidx.lifecycle:lifecycle-runtime-ktx:2.2.0'}

User

package com.zhangyu.myroom.dataimport android.os.Parcelableimport androidx.room.Entityimport androidx.room.PrimaryKeyimport kotlinx.android.parcel.Parcelize@Parcelize@Entity(tableName = "User")data class User( @PrimaryKey var id: String, var name: String) : Parcelable

UserDao

package com.zhangyu.myroom.dataimport androidx.room.*@Daointerface UserDao { @Insert(onConflict = OnConflictStrategy.REPLACE) fun putUser(cacheBean: User) @Query("select * from User where id =:id") suspend fun getUser(id: String): User? @Query("select * from User") suspend fun getAllUser(): List<User>? @Delete fun delete(user: User) @Update(onConflict = OnConflictStrategy.REPLACE) fun update(user: User)}

UserDatabase

package com.zhangyu.myroom.dataimport android.util.Logimport androidx.room.Databaseimport androidx.room.Roomimport androidx.room.RoomDatabaseimport androidx.sqlite.db.SupportSQLiteDatabaseimport com.zhangyu.myroom.Appprivate const val TAG = "CacheDataBase"//后续的数据库升级是根据这个version来比较的，exportSchema导出架构@Database(entities = [User::class], version = 1, exportSchema = false)abstract class UserDatabase : RoomDatabase() { companion object { var dataBase: UserDatabase init { //如果databaseBuilder改为inMemoryDatabaseBuilder则创建一个内存数据库（进程销毁后，数据丢失） dataBase = Room.databaseBuilder(App.context, UserDatabase::class.java, "db_user") //是否允许在主线程进行查询 .allowMainThreadQueries() //数据库创建和打开后的回调，可以重写其中的方法 .addCallback(object : Callback() { override fun onCreate(db: SupportSQLiteDatabase) { super.onCreate(db) Log.d(TAG, "onCreate: db_user") } }) //数据库升级异常之后的回滚 .fallbackToDestructiveMigration() .build() } } abstract fun getUserDao(): UserDao}

MainActivity

package com.zhangyu.myroomimport android.os.Bundleimport android.util.Logimport androidx.appcompat.app.AppCompatActivityimport androidx.lifecycle.lifecycleScopeimport com.zhangyu.myroom.data.Userimport com.zhangyu.myroom.data.UserDatabaseimport kotlinx.coroutines.launchprivate const val TAG = "MainActivity"class MainActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) testCache() } private fun testCache() { val userDao = UserDatabase.dataBase.getUserDao() userDao.putUser(User("1001", "zhangyu")) userDao.putUser(User("1002", "liming")) lifecycleScope.launch { val users = userDao.getAllUser() Log.e(TAG, "users: $users") val user = userDao.getUser("1001") Log.e(TAG, "user: $user") Log.e(TAG, "testCache: 协程执行完毕") } Log.e(TAG, "testCache: ") }}

结果

E/MainActivity: testCache:
E/MainActivity: users: [User(id=1001, name=zhangyu), User(id=1002, name=liming)]
E/MainActivity: user: User(id=1001, name=zhangyu)
E/MainActivity: testCache: 协程执行完毕

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