1，三角色
（1）表：定义一个类，加上注解@Entity，类里需要定义主键，使用@PrimaryKey标识，如果主键自动产生增长，需要加上(autoGenerate = true)，其他变量根据自身业务定义，下面例子定义了一个Student表类：
package com.mike.androidtips.database.room;
import androidx.room.Entity;
import androidx.room.PrimaryKey;
//表
@Entity
public class Student {
@PrimaryKey (autoGenerate = true)
private int id;
int age;
String name;
public Student(int age, String name) {
this.age = age;
this.name = name;
}
public Student() {
}
@Override
public String toString() {
return "Student{" +
"id=" + id +
", age=" + age +
", name='" + name + '\'' +
'}';
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
(2)DAO: Database Access Object, 数据库访问对象类，作用是对数据库中的表进行增删改查操作。在类上加@Dao注解。其他是操作类注解：@Insert， @Update， @Delete， @Query，@Query需要加SQL语句，具体看StudentDao类：
@Dao
public interface StudentDao {
//增
@Insert
public void addStudents(Student...students);
// 删
@Delete
public void deleteStudents(Student...students);
// 删 全部
@Query("DELETE FROM Student")
public void deleteAllStudents();
//改
@Update
public void updateStudents(Student...students);
// 查
@Query("SELECT * FROM Student ORDER BY ID DESC")
public List<Student> getAllStudents();
}
(3) 数据库类：和前面定义的表以及Dao关联起来
- 数据库定义成抽象类
- 数据库类需添加注解@Database，里面定义版本号，以及通过entries关联表
- 需要定义成单例模式
- 定义抽象方法，获取Dao，
@Database(entities = {Student.class}, version = 1, exportSchema = false)
public abstract class StudentDatabase extends RoomDatabase {
private static StudentDatabase INSTANCE;
public static synchronized StudentDatabase getInstance(Context context) {
if (INSTANCE == null) {
INSTANCE = Room.databaseBuilder(context.getApplicationContext(), StudentDatabase.class,
"student database")
//数据库默认是异步线程
//.allowMainThreadQueries() //强制开启主线程也可以用数据库 ，真实环境不要用
.build();
}
return INSTANCE;
}
public abstract StudentDao getStudentDao();
@NonNull
@Override
protected SupportSQLiteOpenHelper createOpenHelper(DatabaseConfiguration config) {
return null;
}
@NonNull
@Override
protected InvalidationTracker createInvalidationTracker() {
return null;
}
@Override
public void clearAllTables() {
}
}
- 数据库的使用，封装一个DBEngine，对外（User）提供增删改查的API。
- DBEngine在构造中获取Dao
- 封装多个AsyncTask操作数据库，把Dao传值进去
- API里调用AsyncTask的execute方法
public class DBEngine {
private StudentDao studentDao;
private String TAG = "DBEngine";
public DBEngine(Context context) {
StudentDatabase database = StudentDatabase.getInstance(context);
studentDao = database.getStudentDao();
}
//插入
public void addStudents(Student...students) {
new AddAsyncTask(studentDao).execute(students);
}
//更新
public void updateStudents(Student...students) {
new UpdateAsyncTask(studentDao).execute(students);
}
//删除单个
public void deleteStudents(Student...students) {
Log.d(TAG, "enter deleteStudents");
new DeleteAsyncTask(studentDao).execute(students);
}
//删除所有
public void deleteAllStudents(){
new DeleteAllAsyncTask(studentDao).execute();
}
//
public void queryAllStudents() {
Log.d("DBEngine", "enter queryAllStudents");
new QueryAsyncTask(studentDao).execute();
}
//插入task
static class AddAsyncTask extends AsyncTask<Student, Void, Void> {
private StudentDao studentDao;
public AddAsyncTask(StudentDao studentDao) {
this.studentDao = studentDao;
}
@Override
protected Void doInBackground(Student... students) {
studentDao.addStudents(students);
return null;
}
}
//更新task
static class UpdateAsyncTask extends AsyncTask<Student, Void, Void> {
private StudentDao studentDao;
public UpdateAsyncTask(StudentDao studentDao) {
this.studentDao = studentDao;
}
@Override
protected Void doInBackground(Student... students) {
studentDao.updateStudents(students);
return null;
}
}
//删除
static class DeleteAsyncTask extends AsyncTask<Student, Void, Void> {
private StudentDao studentDao;
public DeleteAsyncTask(StudentDao studentDao) {
this.studentDao = studentDao;
Log.d("DBEngine", "enter DeleteAsyncTask");
}
@Override
protected Void doInBackground(Student... students) {
studentDao.deleteStudents(students);
Log.d("DBEngine", "enter DeleteAsyncTask, doInBackground");
return null;
}
}
//删除全部
static class DeleteAllAsyncTask extends AsyncTask<Void, Void, Void> {
private StudentDao studentDao;
public DeleteAllAsyncTask(StudentDao studentDao) {
this.studentDao = studentDao;
}
@Override
protected Void doInBackground(Void... voids) {
studentDao.deleteAllStudents();
return null;
}
}
static class QueryAsyncTask extends AsyncTask<Void, Void, Void> {
private StudentDao studentDao;
public QueryAsyncTask(StudentDao studentDao) {
this.studentDao = studentDao;
}
@Override
protected Void doInBackground(Void... voids) {
Log.d("DBEngine" , "QueryAsyncTask doInBackground");
List<Student> allStudents = studentDao.getAllStudents();
Log.d("DBEngine" , "QueryAsyncTask doInBackground, size = " + allStudents.size());
for (Student allStudent : allStudents) {
Log.d("DBEngine" , "全部查询每一项： " + allStudent.toString());
}
return null;
}
}
}
3, User使用DBEngine
public class RoomDatabaseActivity extends Activity {
private String TAG = RoomDatabaseActivity.class.getSimpleName();
private DBEngine dbEngine;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_roomdatabase_layout);
dbEngine = new DBEngine(this);
}
public void insertAction(View view) {
Student student1 = new Student(20, "张三");
Student student2 = new Student(30, "李四");
Student student3 = new Student(15, "王五");
Log.d(TAG, "insertAction...");
dbEngine.addStudents(student1, student2, student3);
}
public void updateAction(View view) {
Student student = new Student(28, "王二麻子");
student.setId(3);
dbEngine.updateStudents(student);
}
public void deleteAction(View view) {
Log.d(TAG, "enter deleteAction");
Student student = new Student();
student.setId(3);
dbEngine.deleteStudents(student);
}
public void queryAction(View view) {
dbEngine.queryAllStudents();
}
public void deleteAll(View view) {
dbEngine.deleteAllStudents();
}
}
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