前言
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Room数据库的创建
1.添加依赖
话不多说：首先要进行依赖，因为我们使用的是kotlin。
所以根据官网提示，在app model的build.gradle文件的dependencies添加：
dependencies {
def room_version = "2.2.6"
implementation "androidx.room:room-runtime:$room_version"
kapt "androidx.room:room-compiler:$room_version"
// optional - Kotlin Extensions and Coroutines support for Room
implementation "androidx.room:room-ktx:$room_version"
}
添加依赖后会报错Could not find method kapt() for arguments。需要添加apply plugin: 'kotlin-kapt'。我会在视频中详细展示。
2.继承RoomDatabase
@Database(
entities = [Teacher::class],
version = 1,
exportSchema = false
)
abstract class BackGardenDatabase : RoomDatabase() {
abstract fun teacherDao(): TeacherDao //这里是非常重要的一步，后面我们来说 ！！！
}
3.创建Teacher类，并使用@Entity注解
@Entity(tableName = "teacher")
class Teacher(
@PrimaryKey
val teacherId: String,
@ColumnInfo(name = "teacher_name")
val teacherName: String,
@Embedded
val student: Student,
)
因为使用到了Student类，
@Entity
class Student(
@PrimaryKey
val studentId: String,
val studentName: String,
)
4.接下来就是比较重要的一步，创建TeacherDao接口，使用@Dao注解。这里就是操作数据库中数据的操作。CRUD（增删改查）。
@Dao
interface TeacherDao {
@Insert(onConflict = OnConflictStrategy.REPLACE)
fun save(teacher: Teacher): Long
@Query("select * from teacher where `teacherId`=:teacherId")
fun getTeacher(teacherId: String): Teacher
@Query("select * from teacher ")
fun getTeachers(): LiveData>
@Delete
fun delete(teacher: Teacher)
@Update(onConflict = OnConflictStrategy.REPLACE)
fun update(teacher: Teacher)
@Query("delete from teacher where `teacherId`=:teacherId")
fun deleteById(teacherId: String);
}
这时，我们就需要在数据库中声明如下代码：
abstract fun teacherDao(): TeacherDao
到这里我们数据库的准备已经差不多了。接下来就是使用的环节。
Room数据库的使用
1.对外提供数据库类，我们来进行操作
class AppModel {
val mMigration: Migration by lazy {
object : Migration(1, 2) {
override fun migrate(database: SupportSQLiteDatabase) {
database.execSQL("alter table teacher rename to teacher1")
database.execSQL("alter table teacher1 add column teach_age INTEGER NOT NULL default 0 ")
}
}
}
val backGardenDatabase: BackGardenDatabase by lazy {
Room.databaseBuilder(
AppGlobals.getApplication(),
BackGardenDatabase::class.java,
"back_garden"
)
//是否允许在主线程查询
// .allowMainThreadQueries()
//没有找到Migration就重新创建数据库
.fallbackToDestructiveMigration()
.addMigrations(mMigration)
//数据库创建和打开的回调
//.addCallback()
//设置查询的线程池
//.setQueryExecutor()
//room的日志模式
//.setJournalMode()
//数据库升级异常后根据指定版本进行回滚
//.fallbackToDestructiveMigrationFrom()
.build()
}
fun providerDB():BackGardenDatabase{
return backGardenDatabase
}
}
2.终于可以使用了，哈哈。创建ViewModel类
class MainViewModel : ViewModel() {
var appModel = AppModel()
val db by lazy {
appModel.providerDB()
}
fun saveTeacher(teacher: Teacher) {
db.teacherDao().save(teacher)
}
val _teachers = MutableLiveData()
fun getTeachers():LiveData>{
return db.teacherDao().getTeachers()
}
fun deleteTeacherById(teacherId: String) {
db.teacherDao().deleteById(teacherId)
}
fun deleteTeacher(teacher: Teacher) {
db.teacherDao().delete(teacher)
}
fun getTeacherById(teacherId: String): Teacher {
return db.teacherDao().getTeacher(teacherId)
}
}
在activity中使用viewModel中定义的方法即可
class MainActivity : AppCompatActivity() {
companion object {
private const val TAG = "MainActivity"
private const val TEACHER_PRE_ID = "100"
private const val STUDENT_PRE_ID = "200"
}
val viewModel: MainViewModel by lazy {
ViewModelProvider(this).get(MainViewModel::class.java)
}
val etStudentName: EditText by lazy {
findViewById(R.id.et_student_name)
}
val etTeacherName: EditText by lazy {
findViewById(R.id.et_teacher_name)
}
val etTeacherId: EditText by lazy {
findViewById(R.id.et_teacher_id)
}
val etStudentId: EditText by lazy {
findViewById(R.id.et_student_id)
}
val showContent: TextView by lazy {
findViewById(R.id.showContent)
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
subscribeUI()
}
private fun subscribeUI() {
viewModel.getTeachers().observe(this, { teachers ->
val stringBuilder = StringBuilder()
teachers.forEach {
stringBuilder.append(it.toString()).append("\n")
}
showContent.text = stringBuilder
})
}
fun insert(view: View) {
val teacher: Teacher = generateTeacher()
viewModel.saveTeacher(teacher)
}
private fun generateTeacher(): Teacher {
val student = generateStudent()
return Teacher("${TEACHER_PRE_ID}${etTeacherId.text}", etTeacherName.text.toString(), student)
}
private fun generateStudent(): Student {
return Student("${STUDENT_PRE_ID}${etStudentId.text}", etStudentName.text.toString())
}
fun delete(view: View) {
if (TextUtils.isEmpty(etTeacherName.text.toString())) {
viewModel.deleteTeacherById(etTeacherId.text.toString())
} else {
var teacher = viewModel.getTeacherById(etTeacherId.text.toString())
viewModel.deleteTeacher(teacher)
}
// viewModel.deleteTeacher(teacher)
}
fun modify(view: View) {
viewModel.updateTeacher(Teacher(etTeacherId.text.toString(),etTeacherName.text.toString(),null))
}
fun query(view: View) {
var teacher = viewModel.getTeacherById(etTeacherId.text.toString())
Log.d(TAG, "query: $teacher")
}
}