删除全部数据:
可以看到,数据全都被删除了。
完整代码可运行项目:Android移动应用开发之使用room实现数据库的增删改查
注意:因为设置表的id是主键且自增,因此插入数据id就会持续增加,因为修改和删除都是在MainActivity中手动设置的,是个比较简单的demo,如果需要看到修改和条件删除的效果
修改此处的setId中的参数即可。
首先需要添加依赖build.gridle中:
def room_version = "2.2.0-alpha01"
implementation "androidx.room:room-runtime:$room_version"
annotationProcessor "androidx.room:room-compiler:$room_version"
定义一张数据表,这里id设置为逐渐且自动增长,就比较方便了。
//一张表
@Entity
public class Student {
//主键唯一,自动增长
@PrimaryKey(autoGenerate = true)
private int id;
private String name;
private int age;
}
然后设置getter和setter的方法,以及带参数的构造方法,就是一个完整的表了:
package demo.demo.room;
import androidx.room.Entity;
import androidx.room.PrimaryKey;
//一张表
@Entity
public class Student {
//主键唯一,自动增长
@PrimaryKey(autoGenerate = true)
private int id;
private String name;
private int age;
public Student(String name, int age) {
this.name = name;
this.age = age;
}
public int getId() {
return id;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
public void setId(int id) {
this.id = id;
}
public void setName(String name) {
this.name = name;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "Student{" +
"id=" + id +
", name='" + name + '\'' +
", age=" + age +
'}';
}
}
然后建立一个StudentDatabase抽象类,用于数据库的创建:
package demo.demo.room;
import android.content.Context;
import androidx.room.Database;
import androidx.room.Room;
import androidx.room.RoomDatabase;
@Database(entities = {Student.class}, version = 1, exportSchema = false)
public abstract class StudentDatabase extends RoomDatabase {
//暴露Dao
public abstract StudentDao getStudentDao();
private static StudentDatabase INSTANCE;
public static synchronized StudentDatabase getInstance(Context context){
if(INSTANCE == null){
INSTANCE = Room.databaseBuilder
(context.getApplicationContext(),
StudentDatabase.class, "student_database")
// .allowMainThreadQueries()
.build();
}
return INSTANCE;
}
}
然后创建一个能对数据库进行增删改查的Dao接口:
package demo.demo.room;
import androidx.room.Dao;
import androidx.room.Delete;
import androidx.room.Insert;
import androidx.room.Query;
import androidx.room.Update;
import java.util.List;
@Dao//对表操作,增删改查
public interface StudentDao {
@Insert
void insertStudents(Student...students);
@Update
void updateStudents(Student...students);
//条件删除
@Delete
void deleteStudents(Student...students);
//删除所有
@Query("DELETE FROM Student")
void deleteAllStudents();
@Query("SELECT * FROM Student ORDER BY ID DESC")
List<Student>getAllStudent();
}
最后就是编写数据库的引擎,具体对数据库进行操作,发挥实质性作用(采用异步操作):
package demo.demo.room.manager;
import android.content.Context;
import android.os.AsyncTask;
import android.util.Log;
import java.util.List;
import demo.demo.room.Student;
import demo.demo.room.StudentDao;
import demo.demo.room.StudentDatabase;
public class DBEngine {
private StudentDao studentDao;
public DBEngine(Context context){
StudentDatabase studentDatabase = StudentDatabase.getInstance(context);
studentDao = studentDatabase.getStudentDao();
}
public void insertStudent(Student...students){
new InsertAsyncTask(studentDao).execute(students);
}
public void updateStudents(Student...students){
new UpdateAsyncTask(studentDao).execute(students);
}
public void deleteStudents(Student...students){
new DeleteAsyncTask(studentDao).execute(students);
}
public void deleteAllStudents(){
new DeleteAllAsyncTask(studentDao).execute();
}
public void queryAllStudents(){
new QueryAllAsyncTask(studentDao).execute();
}
//异步
static class UpdateAsyncTask extends AsyncTask<Student, Void, Void>{
private StudentDao dao;
public UpdateAsyncTask(StudentDao studentDao){
dao = studentDao;
}
@Override
protected Void doInBackground(Student... students) {
dao.updateStudents(students);
return null;
}
}
//条件删除
static class DeleteAsyncTask extends AsyncTask<Student, Void, Void>{
private StudentDao dao;
public DeleteAsyncTask(StudentDao studentDao){
dao = studentDao;
}
@Override
protected Void doInBackground(Student... students) {
dao.deleteStudents(students);
return null;
}
}
//全部删除
static class DeleteAllAsyncTask extends AsyncTask<Void, Void, Void>{
private StudentDao dao;
public DeleteAllAsyncTask(StudentDao studentDao){
dao = studentDao;
}
@Override
protected Void doInBackground(Void... voids) {
dao.deleteAllStudents();
return null;
}
}
static class QueryAllAsyncTask extends AsyncTask<Void, Void, Void>{
private StudentDao dao;
public QueryAllAsyncTask(StudentDao studentDao){
dao = studentDao;
}
@Override
protected Void doInBackground(Void... students) {
List<Student> allStudent = dao.getAllStudent();
//遍历全部查询的结果
for(Student student : allStudent){
Log.e("Hunter", student.toString());
}
return null;
}
}
static class InsertAsyncTask extends AsyncTask<Student, Void, Void>{
private StudentDao dao;
public InsertAsyncTask(StudentDao studentDao){
dao = studentDao;
}
@Override
protected Void doInBackground(Student... students) {
dao.insertStudents(students);
return null;
}
}
}
最后MainActivity进行引擎的调用,对数据库进行操作:
package demo.demo;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import demo.demo.room.Student;
import demo.demo.room.manager.DBEngine;
public class MainActivity extends AppCompatActivity {
private DBEngine dbEngine;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dbEngine = new DBEngine(this);
}
public void insertAction(View view) {
Student student1 = new Student("hunter", 10);
Student student2 = new Student("icy hunter", 10);
dbEngine.insertStudent(student1, student2);
}
public void updateAction(View view) {
Student student = new Student("hunterr", 20);
//修改下标为23的
student.setId(23);
dbEngine.updateStudents(student);
}
public void deleteAction(View view) {
Student student = new Student(null, 0);
student.setId(23);
dbEngine.deleteStudents(student);
}
public void queryAction(View view) {
dbEngine.queryAllStudents();
}
public void deleteAllAction(View view) {
dbEngine.deleteAllStudents();
}
}
上面增删改查的操作和布局中的按钮绑定即可。
运行效果就如开局所示。