Android开发使用Room（SQLite封装）操作数据库

一、Room介绍

           Android采用Sqlite作为数据库存储。Sqlite代码写起来繁琐且容易出错，所以开源社区里逐渐出现了各种ORM（Object Relational Mapping）库。这些开源ORM库都是为了方便Sqlite的使用，包括数据库的创建，升级，增删改查等。常见的ORM有ORMLite，GreenDAO等。Google也意识到了推出自家ORM的必要性，于是有了Room。
           Room和其它ORM库一样，也是在Sqlite上提供了一层抽象。
在介绍Room的使用之前，我们需要先明白几个概念。
Entity：这是一个Model类，对应于数据库中的一张表。Entity类是Sqlite表结构在Java类的映射。
Dao：（Data Access Objects）数据访问对象，顾名思义，我们可以通过它来访问数据。
总的来说就是通过注解的方式操作数据库

二、代码实现

1、添加依赖并同步

在工程build.gradle中添加下面几句

    def room_version = "2.2.0-alpha01"
    implementation "androidx.room:room-runtime:$room_version"
    annotationProcessor "androidx.room:room-compiler:$room_version"
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2、新建一个类通过@Database注解生成一个数据库

StudentDatabase.java

package com.example.learning01;

import android.content.Context;

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

@Database(entities = {Student.class},version = 1,exportSchema = false)//关联数据库
public abstract class StudentDatabase extends RoomDatabase {
    //用户只需要操作DAO
    public abstract StudentDao get_student_dao();
    //单例模式
    private static StudentDatabase studentDatabase;
    public static synchronized StudentDatabase getInstance(Context context){
        if(studentDatabase == null){
            studentDatabase = Room.databaseBuilder(context.getApplicationContext(),StudentDatabase.class,"student_database")
                    //.allowMainThreadQueries() //主线程也能操作数据库 只能测试用
                    .build();
        }
        return studentDatabase;
    }
}
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3、新建一个类通过@Entity注解生成一个表

Student.java

package com.example.learning01;

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

//一张表
@Entity
public class Student {


    @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 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 +
                '}';
    }
}

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4、新建一个类通过@Dao实现增、删、改、查

StudentDao.java

package com.example.learning01;

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 insert_student(Student ... students);

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

    //删
    @Delete
    void delete_student(Student ... students);

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

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

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5、新建一个类通过实现数据库操作，通过异步方式

DBEngine.java

package com.example.learning01;

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

import java.util.List;

public class DBEngine {
    private static final String TAG = "DBEngine";

    private StudentDao studentDao;

    public DBEngine(Context context) {

        StudentDatabase studentDatabase = StudentDatabase.getInstance(context);
        studentDao = studentDatabase.get_student_dao();

    }
    //插入
    public void insert_student(Student ... student) {
        new InsertAsynTask(studentDao).execute(student);
    }
    //更新
    public void update_student(Student ... student) {
        new UpdateAsynTask(studentDao).execute(student);
    }
    //删除
    public void delete_student(Student ... student) {
        new DeleteAsynTask(studentDao).execute(student);
    }
    //全部删除
    public void delete_all_student(Student ... student) {
        new DeleteAllAsynTask(studentDao).execute();
    }
    //全部查询
    public void quary_all_student(Student ... student) {
        new QuaryAllAsynTask(studentDao).execute();
    }


    //开启异步操作
    static class InsertAsynTask extends AsyncTask<Student,Void,Void> {
        private StudentDao studentDao;
        public InsertAsynTask(StudentDao studentDao) {
            this.studentDao = studentDao;
        }

        @Override
        protected Void doInBackground(Student ... students) {
            studentDao.insert_student(students);
            return null;
        }
    }
    static class UpdateAsynTask extends AsyncTask<Student,Void,Void> {
        private StudentDao studentDao;
        public UpdateAsynTask(StudentDao studentDao) {
            this.studentDao = studentDao;
        }

        @Override
        protected Void doInBackground(Student... students) {
            this.studentDao.update_student(students);
            return null;
        }
    }
    static class DeleteAsynTask extends AsyncTask<Student,Void,Void> {
        private StudentDao studentDao;
        public DeleteAsynTask(StudentDao studentDao) {
            this.studentDao = studentDao;
        }

        @Override
        protected Void doInBackground(Student... students) {
            this.studentDao.delete_student(students);
            return null;
        }
    }
    //全部删除
    static class DeleteAllAsynTask extends AsyncTask<Void,Void,Void> {
        private StudentDao studentDao;
        public DeleteAllAsynTask(StudentDao studentDao) {
            this.studentDao = studentDao;
        }
        @Override
        protected Void doInBackground(Void... voids) {
            this.studentDao.delete_all_student();
            return null;
        }
    }
    static class QuaryAllAsynTask extends AsyncTask<Void,Void,Void> {

        private StudentDao studentDao;
        public QuaryAllAsynTask(StudentDao studentDao) {
            this.studentDao = studentDao;
        }

        @Override
        protected Void doInBackground(Void... voids) {
            List<Student> all_student = this.studentDao.get_all_student();
            //遍历全部查询的结果
            for (Student student:all_student)
            {
                Log.i(TAG, "doInBackground: "+student.toString());
            }
            return null;
        }
    }
}

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三、操作数据库

首先定义一个引擎

 private DBEngine dbEngine;
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然后实现

dbEngine = new DBEngine(this);
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完整代码

public class MainActivity extends AppCompatActivity {

    private static final String TAG ="MainActivity";

    private DBEngine dbEngine;

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

        dbEngine = new DBEngine(this);

    }
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1、增

    public void insert_db(View view) {
        Student student1 = new Student("xupeng1",10);
        Student student2 = new Student("xupeng2",20);
        Student student3 = new Student("xupeng3",30);
        Student student4 = new Student("xupeng4",40);


        dbEngine.insert_student(student1,student2,student3,student4);
    }
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2、删

    public void delete_db(View view) {
        Student student = new Student(null,0);
        student.setId(3);
        dbEngine.delete_student(student);
    }

    public void delete_all_db(View view) {
        dbEngine.delete_all_student();
    }
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3、改

    public void update_db(View view) {

        Student student = new Student("weipan",500);
        student.setId(3);
        dbEngine.update_student(student);
    }
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4、查

    public void find_db(View view) {
        dbEngine.quary_all_student();
    }
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四、操作数据库源码

package com.example.learning01;
import androidx.appcompat.app.AppCompatActivity;

import android.annotation.SuppressLint;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.os.Bundle;
import android.util.Log;
import android.view.View;


public class MainActivity extends AppCompatActivity {

    private static final String TAG ="MainActivity";

    private DBEngine dbEngine;

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

        dbEngine = new DBEngine(this);

    }

    public void create_db(View view) {
    }

    public void find_db(View view) {
        dbEngine.quary_all_student();
    }

    public void insert_db(View view) {
        Student student1 = new Student("xupeng1",10);
        Student student2 = new Student("xupeng2",20);
        Student student3 = new Student("xupeng3",30);
        Student student4 = new Student("xupeng4",40);


        dbEngine.insert_student(student1,student2,student3,student4);
    }

    public void update_db(View view) {

        Student student = new Student("weipan",500);
        student.setId(3);
        dbEngine.update_student(student);
    }

    public void delete_db(View view) {
        Student student = new Student(null,0);
        student.setId(3);
        dbEngine.delete_student(student);
    }

    public void delete_all_db(View view) {
        dbEngine.delete_all_student();
    }
}
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