"room.expandProjection":"true"]
}
}
}
}
定义数据表
创建图书表
@Entity(tableName = "book")
class Book {
@PrimaryKey(autoGenerate = true)
var id: Int = 0
@ColumnInfo(name = "bookname")
var name: String? = ""
constructor(bookname: String?) {
this.name = bookname
}
}
表注解解释
1.如果想给一个表设置表名就在@Entity的后面添加(tableName = “book”),不是设置默认采用类名
2.声明表的主键 @PrimaryKey(autoGenerate = true)
3.更改表的属性列名@ColumnInfo(name = “bookname”),默认类的字段名
1.定义Dao类
@Dao
interface BookDao {
@Insert
fun addBook(book : Book)
@Query("SELECT * FROM book")
fun loadAll(): List<Book?>?
@Query("select * from book where name = :name")
fun queryName(name : String) :List<Book?>?
@Delete
fun delete(song: Book?)
}
如果在query时返回值类型和查询的表名和返回值类型或查询的表名不相同时,在程序编译会编译失败,这也降低了程序在运行时出现的风险
2.定义数据库和生成数据类
@Database(entities = [Book::class], version = 1)
abstract class RoomDaoManager : RoomDatabase() {
abstract fun BookDao(): BookDao
companion object {
private val DATABASE_NAME = "dev_db.db"
private var databaseInstance: RoomDaoManager? = null
@Synchronized
open fun getInstance(): RoomDaoManager? {
if (databaseInstance == null) {
databaseInstance = Room
.databaseBuilder(
MyApplication.instance(),
RoomDaoManager::class.java,
DATABASE_NAME
)
.allowMainThreadQueries()
.build()
}
return databaseInstance
}
}
}
数据库升级
1.addMigrations(Migration migrations…):一个迁移可以处理多个版本
2.Migration(int startVersion, int endVersion):每次迁移都可以在定义的两个版本之间移动,初始版本和目标版本
3.在重写的migrate方法中执行更新的sql,同时需要在对应的Entity类中添加相同的字段,来保证字段相同
Room .databaseBuilder(
MyApplication.instance(),
RoomDaoManager::class.java,
DATABASE_NAME
)
.allowMainThreadQueries()
.addMigrations(MIGRATION_1_2)
.build()
###addMigrations(Migration migrations...):一个迁移可以处理多个版本
###Migration:每次迁移都可以在定义的两个版本之间移动
val MIGRATION_1_2 = object : Migration(1, 2) {
override fun migrate(database: SupportSQLiteDatabase) {
//对表增加一个字段
database.execSQL("ALTER TABLE Book ADD COLUMN sn TEXT NOT NULL DEFAULT ''")
}
}
LiveData和Room配合使用
//Livedata依赖
def lifecycle_version = "2.2.0"
implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$lifecycle_version"
//返回值使用Livedata
@Query("SELECT * FROM book where id = :id")
fun queryLiveData(id : Int): LiveData<Book?>?
//通dao对象调用查询的方法
bookDao?.queryLiveData(1)?.observe(this, Observer {
Log.i("book-query","${it?.name}")
})
Rxjava和Room配合使用
//Rxjava2和Rxjava3 可以选择使用
def room_version = "2.3.0"
// optional - RxJava2 support for Room
implementation "androidx.room:room-rxjava2:$room_version"
// optional - RxJava3 support for Room
implementation "androidx.room:room-rxjava3:$room_version"
