46. Room

标签：room 46 void Student import android public Room

46. Room
46.1 Room三角色介绍
→ → Room 是SQLite数据库的抽象

流畅易用的访问数据库。

Entity ：Student
DAO ：DAO
DB：StudentDatabase
注解

46.2 Room三角色编写
引入依赖

implementation 'androidx.room:room-runtime:2.4.3'
annotationProcessor 'androidx.room:room-compiler:2.4.3'

同步

编写三角色

Student.java

package com.dingjiaxiong.room;

import androidx.room.Entity;
import androidx.room.PrimaryKey;

@Entity
public class Student {

@PrimaryKey(autoGenerate = true)
private int id;

private String name;

private int age;

@Override
public String toString() {
return "Student{" +
"id=" + id +
", name='" + name + '\'' +
", age=" + age +
'}';
}

public Student(int id, String name, int age) {
this.id = id;
this.name = name;
this.age = age;
}

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}
}

StudentDAO.java

package com.dingjiaxiong.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
public interface StudentDAO {

//增
@Insert
void insertStudents(Student ... students);

//改
@Update
void updateStudents(Student ... students);

//删
@Query("DELETE FROM Student")
void deleteAllStudents();

//查
@Query("SELECT * FROM Student ORDER BY ID DESC")
List<Student> getAllStudent();
}

StudentDatabase.java

package com.dingjiaxiong.room;

import android.content.Context;

import androidx.room.Database;
import androidx.room.Room;
import androidx.room.RoomDatabase;

//数据库关联
@Database(entities = {Student.class},version = 1,exportSchema = false)
public abstract class StudentDatabase extends RoomDatabase {

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")
//默认异步线程
// .allowMainThreadQueries()
.build();
}

return INSTANCE;
}

}

46.3 Room实战
用户只需要拿DAO

布局

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
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"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity2"
android:orientation="vertical">

</LinearLayout>

Student.java

package com.dingjiaxiong.room;

import androidx.room.Entity;
import androidx.room.PrimaryKey;

// 一张表（主键唯一主键自动增长， name，age）
@Entity
public class Student {

// 主键唯一主键自动增长
@PrimaryKey(autoGenerate = true)
private int id;

private String name;

private int age;

/*public Student() {
}*/

public Student(String name, int age) {
this.name = name;
this.age = age;
}

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}

@Override
public String toString() {
return "Student{" +
"id=" + id +
", name='" + name + '\'' +
", age=" + age +
'}';
}
}

StudentDatabase.java

package com.dingjiaxiong.room;

import android.content.Context;

import androidx.room.Database;
import androidx.room.Room;
import androidx.room.RoomDatabase;

//数据库关联
@Database(entities = {Student.class},version = 1,exportSchema = false)
public abstract class StudentDatabase extends RoomDatabase {

public abstract StudentDao getStudentDao();

return INSTANCE;
}

}

StudentDao.java

package com.dingjiaxiong.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 // Database access object == 对表进行增删改查
public interface StudentDao {

// 增
@Insert
void insertStudents(Student ... students);

// 改
@Update
void updateStudents(Student... students);

// 删条件
@Delete
void deleteStudents(Student... students);

// 删除所有 @Delete 单个条件删除用的
@Query("DELETE FROM Student")
void deleteAllStudents();

// 查询所有倒序查询
@Query("SELECT * FROM Student ORDER BY ID DESC")
List<Student> getAllStudent();
}

DBEngine.java

package com.dingjiaxiong.room.manager;

import android.content.Context;
import android.os.AsyncTask;
import android.util.Log;

import com.dingjiaxiong.room.Student;
import com.dingjiaxiong.room.StudentDao;
import com.dingjiaxiong.room.StudentDatabase;

import java.util.List;

// DB的引擎
public class DBEngine {

// 只需要拿到dao，就能够对数据库增删改查了
private StudentDao studentDao;

public DBEngine(Context context) {
StudentDatabase studentDatabase = StudentDatabase.getInstance(context);
studentDao = studentDatabase.getStudentDao();
}

// dao 增删改查

// insert 插入
public void insertStudents(Student... students) {
new InsertAsyncTask(studentDao).execute(students);
}

// update 更新
public void updateStudents(Student... students) {
new UpdateAsyncTask(studentDao).execute(students);
}

// delete 删除条件
public void deleteStudents(Student... students) {
new DeleteAsyncTask(studentDao).execute(students);
}

// delete 全部删除
public void deleteAllStudents() {
new DeleteAllAsyncTask(studentDao).execute();
}

// 查询全部
public void queryAllStudents() {
new QueryAllAsyncTask(studentDao).execute();
}

// 如果我们想玩数据库默认是异步线程 ============ 异步操作

// insert 插入
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;
}
}

// update 更新
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;
}
}

// delete 删除条件
static class DeleteAsyncTask extends AsyncTask<Student, Void, Void> {

private StudentDao dao;

public DeleteAsyncTask(StudentDao studentDao) {
dao = studentDao;
}

@Override
protected Void doInBackground(Student... students) { // 既然传递了 student 进来，就是条件删除
dao.deleteStudents(students);
return null;
}
}

// 删除全部删除
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;
}
}

// 全部查询
private static class QueryAllAsyncTask extends AsyncTask<Void, Void, Void> {

private StudentDao dao;

public QueryAllAsyncTask(StudentDao studentDao) {
dao = studentDao;
}

@Override
protected Void doInBackground(Void... voids) {
List<Student> allStudent = dao.getAllStudent();

// 遍历全部查询的结构
for (Student student : allStudent) {
Log.e("Derry", "doInBackground: 全部查询每一项：" + student.toString() );
}

return null;
}
}

}

MainActivity2.java

package com.dingjiaxiong.mysqlite;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;

import com.dingjiaxiong.room.Student;
import com.dingjiaxiong.room.manager.DBEngine;

// Room 的学习
public class MainActivity2 extends AppCompatActivity {

private DBEngine dbEngine;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main2);

dbEngine = new DBEngine(this);
}

/**
* 插入
* @param view
*/
public void insertAction(View view) {
Student student1 = new Student("张三", 20);
Student student2 = new Student("李四", 23);
Student student3 = new Student("王五", 27);
dbEngine.insertStudents(student1, student2, student3);
}

/**
* 修改下标为 3 修改成："李元霸", 40
* @param view
*/
public void updateAction(View view) {
Student student = new Student("李元霸", 40);
student.setId(3);
dbEngine.updateStudents(student);
}

/**
* 删除条件下标为 3
* @param view
*/
public void deleteAction(View view) {
Student student = new Student(null, 0);
student.setId(3);
dbEngine.deleteStudents(student);
}

/**
* 查询
* @param view
*/
public void queryAction(View view) {
dbEngine.queryAllStudents();
}

/**
* 全部删除
* @param view
*/
public void deleteAllAction(View view) {
dbEngine.deleteAllStudents();
}
}

运行

在这里插入图片描述

标签：room,46,void,Student,import,android,public,Room
From： https://www.cnblogs.com/55zjc/p/16709772.html

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