这是我如何使用房间持久性库插入数据到数据库:
实体:
@Entity
class User {
@PrimaryKey(autoGenerate = true)
public int id;
//...
}
数据访问对象:
@Dao
public interface UserDao{
@Insert(onConflict = IGNORE)
void insertUser(User user);
//...
}
是否有可能返回用户的id一旦插入完成在上面的方法本身，而不编写一个单独的选择查询?
当前回答
根据文档中标注了@Insert的函数可以返回rowId。
如果@Insert方法只接收到1个参数，它可以返回一个long，即插入项的新rowId。如果参数是数组或集合，则应该返回long[]或List< long >。
我有这个问题是，它返回rowId而不是id，我仍然没有找到如何使用rowId获得id。
编辑:我现在知道如何从rowId获取id。下面是SQL命令:
SELECT id FROM table_name WHERE rowid = :rowId
其他回答
在你的Dao中，插入查询返回Long，即插入的rowId。
@Insert(onConflict = OnConflictStrategy.REPLACE)
fun insert(recipes: CookingRecipes): Long
在你的模型(存储库)类中:(MVVM)
fun addRecipesData(cookingRecipes: CookingRecipes): Single<Long>? {
return Single.fromCallable<Long> { recipesDao.insertManual(cookingRecipes) }
}
在你的ModelView类中:(MVVM)用DisposableSingleObserver处理LiveData。 工作源代码参考:https://github.com/SupriyaNaveen/CookingRecipes
根据下面的文档(代码片段下面)
使用@Insert注释的方法可以返回:
长单次插入操作 long[]或long[]或List< long >用于多个插入操作 如果你不关心插入的id，则为空
经过一番努力，我终于解决了这个问题。以下是我使用MMVM架构的解决方案:
Student.kt
@Entity(tableName = "students")
data class Student(
@NotNull var name: String,
@NotNull var password: String,
var subject: String,
var email: String
) {
@PrimaryKey(autoGenerate = true)
var roll: Int = 0
}
StudentDao.kt
interface StudentDao {
@Insert
fun insertStudent(student: Student) : Long
}
StudentRepository.kt
class StudentRepository private constructor(private val studentDao: StudentDao)
{
fun getStudents() = studentDao.getStudents()
fun insertStudent(student: Student): Single<Long>? {
return Single.fromCallable(
Callable<Long> { studentDao.insertStudent(student) }
)
}
companion object {
// For Singleton instantiation
@Volatile private var instance: StudentRepository? = null
fun getInstance(studentDao: StudentDao) =
instance ?: synchronized(this) {
instance ?: StudentRepository(studentDao).also { instance = it }
}
}
}
StudentViewModel.kt
class StudentViewModel (application: Application) : AndroidViewModel(application) {
var status = MutableLiveData<Boolean?>()
private var repository: StudentRepository = StudentRepository.getInstance( AppDatabase.getInstance(application).studentDao())
private val disposable = CompositeDisposable()
fun insertStudent(student: Student) {
disposable.add(
repository.insertStudent(student)
?.subscribeOn(Schedulers.newThread())
?.observeOn(AndroidSchedulers.mainThread())
?.subscribeWith(object : DisposableSingleObserver<Long>() {
override fun onSuccess(newReturnId: Long?) {
Log.d("ViewModel Insert", newReturnId.toString())
status.postValue(true)
}
override fun onError(e: Throwable?) {
status.postValue(false)
}
})
)
}
}
在片段中:
class RegistrationFragment : Fragment() {
private lateinit var dataBinding : FragmentRegistrationBinding
private val viewModel: StudentViewModel by viewModels()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
initialiseStudent()
viewModel.status.observe(viewLifecycleOwner, Observer { status ->
status?.let {
if(it){
Toast.makeText(context , "Data Inserted Sucessfully" , Toast.LENGTH_LONG).show()
val action = RegistrationFragmentDirections.actionRegistrationFragmentToLoginFragment()
Navigation.findNavController(view).navigate(action)
} else
Toast.makeText(context , "Something went wrong" , Toast.LENGTH_LONG).show()
//Reset status value at first to prevent multitriggering
//and to be available to trigger action again
viewModel.status.value = null
//Display Toast or snackbar
}
})
}
fun initialiseStudent() {
var student = Student(name =dataBinding.edName.text.toString(),
password= dataBinding.edPassword.text.toString(),
subject = "",
email = dataBinding.edEmail.text.toString())
dataBinding.viewmodel = viewModel
dataBinding.student = student
}
}
我使用过数据绑定。这是我的XML:
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools">
<data>
<variable
name="student"
type="com.kgandroid.studentsubject.data.Student" />
<variable
name="listener"
type="com.kgandroid.studentsubject.view.RegistrationClickListener" />
<variable
name="viewmodel"
type="com.kgandroid.studentsubject.viewmodel.StudentViewModel" />
</data>
<androidx.core.widget.NestedScrollView
android:id="@+id/nestedScrollview"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fillViewport="true"
tools:context="com.kgandroid.studentsubject.view.RegistrationFragment">
<androidx.constraintlayout.widget.ConstraintLayout
android:id="@+id/constarintLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:isScrollContainer="true">
<TextView
android:id="@+id/tvRoll"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginTop="16dp"
android:layout_marginEnd="16dp"
android:gravity="center_horizontal"
android:text="Roll : 1"
android:textColor="@color/colorPrimary"
android:textSize="18sp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<EditText
android:id="@+id/edName"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="24dp"
android:layout_marginEnd="16dp"
android:ems="10"
android:inputType="textPersonName"
android:text="Name"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toBottomOf="@+id/tvRoll" />
<TextView
android:id="@+id/tvName"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginEnd="16dp"
android:text="Name:"
android:textColor="@color/colorPrimary"
android:textSize="18sp"
app:layout_constraintBaseline_toBaselineOf="@+id/edName"
app:layout_constraintEnd_toStartOf="@+id/edName"
app:layout_constraintStart_toStartOf="parent" />
<TextView
android:id="@+id/tvEmail"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Email"
android:textColor="@color/colorPrimary"
android:textSize="18sp"
app:layout_constraintBaseline_toBaselineOf="@+id/edEmail"
app:layout_constraintEnd_toStartOf="@+id/edEmail"
app:layout_constraintStart_toStartOf="parent" />
<EditText
android:id="@+id/edEmail"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="24dp"
android:layout_marginEnd="16dp"
android:ems="10"
android:inputType="textPersonName"
android:text="Name"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toBottomOf="@+id/edName" />
<TextView
android:id="@+id/textView6"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Password"
android:textColor="@color/colorPrimary"
android:textSize="18sp"
app:layout_constraintBaseline_toBaselineOf="@+id/edPassword"
app:layout_constraintEnd_toStartOf="@+id/edPassword"
app:layout_constraintStart_toStartOf="parent" />
<EditText
android:id="@+id/edPassword"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="24dp"
android:layout_marginEnd="16dp"
android:ems="10"
android:inputType="textPersonName"
android:text="Name"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toBottomOf="@+id/edEmail" />
<Button
android:id="@+id/button"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="32dp"
android:layout_marginTop="24dp"
android:layout_marginEnd="32dp"
android:background="@color/colorPrimary"
android:text="REGISTER"
android:onClick="@{() -> viewmodel.insertStudent(student)}"
android:textColor="@android:color/background_light"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/edPassword" />
</androidx.constraintlayout.widget.ConstraintLayout>
</androidx.core.widget.NestedScrollView>
</layout>
我已经挣扎了很多，以完成这与asynctask作为房间插入和删除操作必须在一个单独的线程。终于能够做到这一点与单一 RxJava中的type可观察对象。
下面是Gradle对rxjava的依赖关系:
implementation 'io.reactivex.rxjava2:rxandroid:2.0.1'
implementation 'io.reactivex.rxjava2:rxjava:2.0.3'
@Insert函数可以返回void, long, long[]或List< long >。请尝尝这个。
@Insert(onConflict = OnConflictStrategy.REPLACE)
long insert(User user);
// Insert multiple items
@Insert(onConflict = OnConflictStrategy.REPLACE)
long[] insert(User... user);
如果语句成功，一条记录的插入返回值将为1。
如果你想插入对象列表，你可以使用:
@Insert(onConflict = OnConflictStrategy.REPLACE)
public long[] addAll(List<Object> list);
然后用Rx2执行:
Observable.fromCallable(new Callable<Object>() {
@Override
public Object call() throws Exception {
return yourDao.addAll(list<Object>);
}
}).subscribeOn(Schedulers.io()).observeOn(AndroidSchedulers.mainThread()).subscribe(new Consumer<Object>() {
@Override
public void accept(@NonNull Object o) throws Exception {
// the o will be Long[].size => numbers of inserted records.
}
});
