3.31

所花时间（包括上课）：2

打码量(行)：350

博客量(篇)：1

了解到知识点：学习Room

 

 import androidx.room.Entity;

import androidx.room.PrimaryKey;

 

@Entity(tableName = "users")

public class User {

 

    @PrimaryKey(autoGenerate = true)

    private int id;

 

    private String name;

 

    private String email;

 

    public User(String name, String email) {

        this.name = name;

        this.email = email;

    }

 

    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 String getEmail() {

        return email;

    }

 

    public void setEmail(String email) {

        this.email = email;

    }

}

import androidx.room.Dao;

import androidx.room.Insert;

import androidx.room.Query;

import java.util.List;

 

@Dao

public interface UserDao {

 

    @Insert

    void insert(User user);

 

    @Query("SELECT * FROM users")

    List<User> getAllUsers();

 

    @Query("SELECT * FROM users WHERE id = :userId")

    User getUserById(int userId);

 

    // 可以定义更多的查询方法和操作方法

}

import androidx.room.Database;

import androidx.room.RoomDatabase;

 

@Database(entities = {User.class}, version = 1, exportSchema = false)

public abstract class MyAppDatabase extends RoomDatabase {

 

    public abstract UserDao userDao();

}

import android.content.Context;

import androidx.room.Room;

 

public class DatabaseClient {

 

    private final Context context;

    private static DatabaseClient mInstance;

 

    // Room 数据库实例

    private MyAppDatabase appDatabase;

 

    private DatabaseClient(Context context) {

        this.context = context;

 

        // 创建或获取 Room 数据库实例

        appDatabase = Room.databaseBuilder(context.getApplicationContext(),

                MyAppDatabase.class, "my_database")

                .fallbackToDestructiveMigration() // 数据库升级时使用，清除所有数据重新创建

                .build();

    }

 

    public static synchronized DatabaseClient getInstance(Context context) {

        if (mInstance == null) {

            mInstance = new DatabaseClient(context);

        }

        return mInstance;

    }

 

    public MyAppDatabase getAppDatabase() {

        return appDatabase;

    }

}