Android数据存储:SQLite、Room

Android Room 是 Android 官方提供的一个持久性库，用于在 Android 应用程序中管理数据库。它提供了一个对象关系映射（ORM）层，允许您在应用程序中使用对象来表示数据库表和数据行，并自动生成与之相关的SQL查询和操作。

Room使用

def room_version = "2.6.1"

    implementation "androidx.room:room-runtime:$room_version"
    annotationProcessor "androidx.room:room-compiler:$room_version"

2.创建一个数据实体类：实体表示应用的数据库中的表。数据实体用于更新表中的行所存储的数据以及创建新行供插入。

使用 Room 实体定义数据  |  Android Developers (google.cn)

3.创建一个数据访问对象 (DAO)：提供在数据库中查询、更新、插入和删除数据的方法。

使用 Room DAO 访问数据  |  Android Developers (google.cn)

4.创建一个数据库类：数据库类用于定义实体和数据访问对象的列表。它也是底层连接的主要访问点。

@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")

                    .build();
        }

        return INSTANCE;
    }

}

• 该类必须带有@Database注解，entities指明包含的实体， version表明版本，将 version 设为 1。每当更改数据库表的架构时，都必须提升版本号。将 exportSchema 设为 false，这样就不会保留架构版本记录的备份。
• 该类必须是一个抽象类，用于继承RoomDatabase。
• 对于与数据库关联的每个 DAO 类，数据库类必须定义一个具有零参数的抽象方法，并返回 DAO 类的实例。
• 使用Room的Room.databaseBuilder创建数据库。不过，仅当该数据库不存在时才应创建。否则，请返回现有数据库。

5.创建一个类实现数据库异步操作

public class DBEngine {
    private StudentDao studentDao;

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

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

    public  void deleteStudents(Student... students){
        new DeleteAsyncTask(studentDao).execute(students);
    }

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

    public  void deleteAllStudent(){
        new DeleteAllAsyncTask(studentDao).execute();
    }

    public  void queryStudents(){
        new QueryAllAsyncTask(studentDao).execute();
    }

    //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;
        }
    }

    //修改
    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;
        }
    }

    //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;
        }
    }

    //全部查询
    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> allStudents = dao.getAllStudents();
            for (Student s : allStudents) {
                Log.e("search", "doInBackground:全部查询每一项"+ s.toString() );
            }
            return null;
        }
    }

6.MainActivity

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);
    }

    public void insertAction(View view) {
        Student student = new Student("jerry",8);
        Student student1 = new Student("tom",9);
        Student student2 = new Student("jack",10);
        dbEngine.insertStudents(student,student1,student2);
    }

    public void deleteAction(View view) {
        Student student = new Student(null,0);
        student.setId(2);
        dbEngine.deleteStudents(student);
    }

    public void updateAction(View view) {
        Student student = new Student("lili",20);
        student.setId(3);
        dbEngine.updateStudents(student);
    }

    public void queryAction(View view) {
        dbEngine.queryStudents();
    }

    public void deleteAllAction(View view) {
        dbEngine.deleteAllStudent();
    }
}