46. 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">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="插入"
android:onClick="insertAction"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="修改"
android:onClick="updateAction"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="删除"
android:onClick="deleteAction"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="查询"
android:onClick="queryAction"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="全部删除"
android:onClick="deleteAllAction"
/>
</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();
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;
}
}
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
