Jetpack Architecture系列教程之(五)——Room ORM库

最新推荐文章于 2025-04-24 16:14:04 发布

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最新推荐文章于 2025-04-24 16:14:04 发布

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分类专栏： Jetpack Architecture系列教程文章标签： android jetpack

本文链接：https://blog.youkuaiyun.com/heludoit1/article/details/145756354

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介绍

Room是基于SQLite实现的，一款具备比较全面的SQLite功能的ORM库。可以理解为它是对SQLite的增强优化版。

平时在日常开发中，ORM库用得比较多的是GreenDao、LitePal、Realm等优秀的开源库，但是它们都是第三方的。而如今Google自己推出了一款ORM库，也就是本篇要介绍的Room。毕竟是亲儿子，我们作为Android开发者找不到不去学习它的理由。接下来我们一起来看看吧。

（Tips：ORM是建立关系对象映射，也就是我们常用到的数据持久）

如何使用？

添加依赖

// room
def room_version = '2.2.0-alpha01'
implementation "androidx.room:room-runtime:$room_version"
implementation "androidx.room:room-ktx:$room_version"
kapt "androidx.room:room-compiler:$room_version"
annotationProcessor "android.arch.persistence.room:compiler:$room_version"
kapt "android.arch.persistence.room:compiler:$room_version"

初始化DB

class App: Application() {
    companion object{
        var instance: App? = null
    }
    var db: AppDatabase? = null
    override fun onCreate() {
        super.onCreate()
        instance = this
        db = Room.databaseBuilder(
            applicationContext,
            AppDatabase::class.java, "db_book"
        ).build()
    }
}

建立实体类

@Entity
data class BookBean(
    @PrimaryKey var uid: Int,
    @ColumnInfo(name = "book_name") var bookName: String?,
    @ColumnInfo(name = "is_like") var isLike: Boolean?
)

建立Dao层

@Dao
interface BookDao {

    @Insert
    fun insertAll(books: List<BookBean>)

    @Delete
    fun delete(book: BookBean)

    @Update
    fun updateBook(book: BookBean)

    @Query("SELECT * FROM bookbean")
    fun getAll(): List<BookBean>

    @Query("SELECT * FROM bookbean WHERE is_like IN (:isLike)")
    fun getAllByLike(isLike: Boolean): List<BookBean>


}

@Database(entities = [BookBean::class], version = 1,exportSchema = false)
abstract class AppDatabase : RoomDatabase() {

    abstract fun bookDao(): BookDao

    //...Other Dao

}

Dao层业务实现

// Room added data
val bookStore = arrayOf("...")
val books: MutableList<BookBean> = mutableListOf()
for ((index, bookName) in bookStore.withIndex()){
    val book = BookBean(index,bookName,false)
    books.add(book)
}
App.instance?.db?.bookDao()?.insertAll(books)

doAsync {
    // Room delete data
    val delResult = App.instance?.db?.bookDao()?.delete(datas[position])
    if(null != delResult){
        uiThread {
            datas -= datas[position]
            notifyDataSetChanged()
        }
    }
}

doAsync {
    // Room update data
    datas[position].isLike = !datas[position].isLike!!
    App.instance?.db?.bookDao()?.updateBook(datas[position])

    uiThread {
        notifyDataSetChanged()
    }
}

doAsync {
    // Query data for Room
    mDatas = App.instance?.db?.bookDao()?.getAll()!!
    if(mDatas.isEmpty()){
        initData()
    }
    uiThread {
        mBookAdapter = BookAdapter(this@BookActivity,mDatas)
        mRecyclerView.adapter = mBookAdapter
        mBookAdapter.notifyDataSetChanged()
    }
}

doAsync {
    // Query like data for Room
    mDatas = App.instance?.db?.bookDao()?.getAllByLike(true)!!
    uiThread {
        if(mDatas.isNotEmpty()){
            for(bookBean:BookBean in mDatas){
                mStringBuilder.append(bookBean.bookName)
                mStringBuilder.append(",")
            }
            mTvLike.text = "喜欢的书：$mStringBuilder"
        }else{
            mTvLike.text = "喜欢的书：暂无（请在主页添加）"
        }
    }
}