一、前言
Room是一个持久层库，它可以使我们更加方便的操作SQLite数据库。下面我们介绍它的具体使用。
二、Room的使用介绍
1、创建User实体
package com.jilian.androidarchitecture.common;import android.arch.persistence.room.ColumnInfo;import android.arch.persistence.room.Embedded;import android.arch.persistence.room.Entity;import android.arch.persistence.room.Ignore;import android.arch.persistence.room.PrimaryKey;/**
* 实体类
*/@Entity(tableName = "user")public class UserDto { //主键 自增长
@PrimaryKey(autoGenerate = true) //表名
@ColumnInfo(name = "id") private Long id; @ColumnInfo(name = "sex") private String sex; @ColumnInfo(name = "username") private String username; @ColumnInfo(name = "password") private String password; // 指示 Room 需要忽略的字段或方法
@Ignore
private String age; //把 info内嵌到 UserDto中
@Embedded
private UserInfo info; public UserInfo getInfo() { return info;
} public void setInfo(UserInfo info) { this.info = info;
} public Long getId() { return id;
} public void setId(Long id) { this.id = id;
} public String getAge() { return age;
} public void setAge(String age) { this.age = age;
} public String getSex() { return sex;
} public void setSex(String sex) { this.sex = sex;
} public String getPassword() { return password;
} public void setPassword(String password) { this.password = password;
} public String getUsername() { return username;
} public void setUsername(String username) { this.username = username;
} @Override
public String toString() { return "UserDto{" + "id=" + id + ", username='" + username + '\'' + ", password='" + password + '\'' + '}';
}
}下面介绍实体中的注解含义：
@Entity(tableName = "user") 指数据表名为 user
@PrimaryKey(autoGenerate = true) 设置主键，autoGenerate = true 指主键自增长
@ColumnInfo(name = "sex") 列名
@Ignore 需要忽略的字段或方法
@Embedded 把其他实体嵌入到该实体，也就是说，该数据表将拥有其他数据表的属性
2、创建操作数据库的DAO
package com.jilian.androidarchitecture.dao;import android.arch.lifecycle.LiveData;import android.arch.persistence.room.Dao;import android.arch.persistence.room.Delete;import android.arch.persistence.room.Insert;import android.arch.persistence.room.Query;import android.arch.persistence.room.Update;import com.jilian.androidarchitecture.common.UserDto;import java.util.List;import io.reactivex.Flowable;/**
* 操作数据库的dao层 接口
*/@Daopublic interface UserDao { /**
* 查询用户列表
* @return
*/
@Query("select * from user") List<UserDto> findUserList(); /**
* 添加用户
* @param userDtos 可变参数 可以多个
*/
@Insert
void addUser(UserDto...userDtos); /**
* 根据ID查询用户
* @param ids 可以多个ID 查询多个用户
*/
@Query("select * from user where id in (:ids)") List<UserDto> findUserById(Long[] ids); /**
* 更加用户名查询
* @param username
* @return
*/
@Query("select * from user where username = (:username)") List<UserDto> findUserByName(String username); /**
* 删除用户
* @param userDtos
*/
@Delete
void deleteUser(UserDto...userDtos); /**
* 更新用户
* @param userDtos
*/
@Update
void updateUser(UserDto...userDtos); /**
* 结合 LiveData使用
* @return
*/
@Query("select * from user")
LiveData<List<UserDto>> findUserListForLiveData(); /**
* 结合RxJava使用
* @return
*/
@Query("select * from user")
Flowable<List<UserDto>> findUserListFoRxJava();
}在DAO层我们定义了常规的增删改查的方法，同时我们可以配合LiveData和RxJava一起使用。
3、初始化数据库
package com.jilian.androidarchitecture.db;import android.arch.persistence.room.Database;import android.arch.persistence.room.Room;import android.arch.persistence.room.RoomDatabase;import android.content.Context;import com.jilian.androidarchitecture.common.UserDto;import com.jilian.androidarchitecture.common.UserInfo;import com.jilian.androidarchitecture.dao.UserDao;/**
* 创建数据库
*/@Database(entities = {UserDto.class,UserInfo.class},version = 1)public abstract class AppDataBase extends RoomDatabase { private static AppDataBase appDataBase; //对外提供需要操作数据库的DAO
public abstract UserDao getUserDao(); /**
* 以单实例的形式初始化数据 并对外提供 AppDataBase实例
* @param context
* @return
*/
public static AppDataBase getInstance(Context context){ if(appDataBase==null){ synchronized (AppDataBase.class){ if(appDataBase==null){ //"user" 为数据库名
appDataBase = Room.databaseBuilder(context.getApplicationContext(),AppDataBase.class,"user_data").build();
}
}
} return appDataBase;
}
}初始化数据库需要创建抽象类并继承RoomDatabase，我们使用Database 注解，并指定相应的实体创建数据表，和数据库版本 version。并在抽象类中创建获取DAO的方法 。
//对外提供需要操作数据库的DAO public abstract UserDao getUserDao();
然后我们通过单实例的方式初始化数据库，并对外提供RoomDatabase实例。
/**
* 以单实例的形式初始化数据 并对外提供 AppDataBase实例
* @param context
* @return
*/
public static AppDataBase getInstance(Context context){ if(appDataBase==null){ synchronized (AppDataBase.class){ if(appDataBase==null){ //"user" 为数据库名
appDataBase = Room.databaseBuilder(context.getApplicationContext(),AppDataBase.class,"user_data").build();
}
}
} return appDataBase;
}我们通过RoomDatabase实例可以拿到DAO对象，接着通过DAO对象即可对数据表进行操作。
下面我们通过例子来介绍：
三、实例
创建RoomActivity，分别对数据库进行增删改查的操作
package com.jilian.androidarchitecture;import android.arch.lifecycle.LiveData;import android.arch.lifecycle.Observer;import android.os.Bundle;import android.support.annotation.Nullable;import android.support.v7.app.AppCompatActivity;import android.util.Log;import android.view.View;import android.widget.TextView;import com.jilian.androidarchitecture.common.UserDto;import com.jilian.androidarchitecture.db.AppDataBase;import org.reactivestreams.Subscriber;import org.reactivestreams.Subscription;import java.util.List;import io.reactivex.Flowable;import io.reactivex.android.schedulers.AndroidSchedulers;import io.reactivex.schedulers.Schedulers;public class RoomActivity extends AppCompatActivity { private static final String TAG = "RoomActivity"; private TextView add; private TextView update; private TextView delete; private TextView query; private TextView queryList; private TextView queryLiveData; private TextView queryRxJava; @Override
protected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState);
setContentView(R.layout.activity_room);
add = (TextView) findViewById(R.id.add);
update = (TextView) findViewById(R.id.update);
delete = (TextView) findViewById(R.id.delete);
query = (TextView) findViewById(R.id.query);
queryList = (TextView) findViewById(R.id.queryList);
queryLiveData = (TextView) findViewById(R.id.queryLiveData);
queryRxJava = (TextView) findViewById(R.id.queryRxJava);
add.setOnClickListener(new View.OnClickListener() { @Override
public void onClick(View v) { new Thread() { @Override
public void run() { super.run();
UserDto userDto = new UserDto();
userDto.setUsername("daxiaa");
userDto.setPassword("123456");
AppDataBase.getInstance(RoomActivity.this).getUserDao().addUser(userDto);
}
}.start();
}
});
update.setOnClickListener(new View.OnClickListener() { @Override
public void onClick(View v) { new Thread() { @Override
public void run() { super.run();
UserDto userDto = new UserDto();
userDto.setUsername("zaizai");
userDto.setId(1l);
userDto.setPassword("111111");
AppDataBase.getInstance(RoomActivity.this).getUserDao().updateUser(userDto);
}
}.start();
}
});
delete.setOnClickListener(new View.OnClickListener() { @Override
public void onClick(View v) { new Thread() { @Override
public void run() { super.run();
UserDto userDto = new UserDto();
userDto.setId(1l);
AppDataBase.getInstance(RoomActivity.this).getUserDao().deleteUser(userDto);
}
}.start();
}
});
query.setOnClickListener(new View.OnClickListener() { @Override
public void onClick(View v) { new Thread() { @Override
public void run() { super.run();
List<UserDto> list = AppDataBase.getInstance(RoomActivity.this).getUserDao().findUserByName("zaizai"); for (int i = 0; i < list.size(); i++) {
Log.e(TAG, "user:" + list.get(i).toString());
;
}
}
}.start();
}
});
queryList.setOnClickListener(new View.OnClickListener() { @Override
public void onClick(View v) { new Thread() { @Override
public void run() { super.run();
List<UserDto> list = AppDataBase.getInstance(RoomActivity.this).getUserDao().findUserList(); for (int i = 0; i < list.size(); i++) {
Log.e(TAG, "user:" + list.get(i).toString());
;
}
}
}.start();
}
});
queryLiveData.setOnClickListener(new View.OnClickListener() { @Override
public void onClick(View v) { new Thread() { @Override
public void run() { super.run();
LiveData<List<UserDto>> userListForLiveData = AppDataBase.getInstance(RoomActivity.this).getUserDao().findUserListForLiveData();
userListForLiveData.observe(RoomActivity.this, new Observer<List<UserDto>>() { @Override
public void onChanged(@Nullable List<UserDto> list) { if (list != null) { for (int i = 0; i < list.size(); i++) {
Log.e(TAG, "user:" + list.get(i).toString());
}
}
}
});
}
}.start();
}
});
queryRxJava.setOnClickListener(new View.OnClickListener() { @Override
public void onClick(View v) {
Flowable<List<UserDto>> list = AppDataBase.getInstance(RoomActivity.this).getUserDao().findUserListFoRxJava(); //IO 线程获取数据
list.subscribeOn(Schedulers.io()) //线程切换
.observeOn(AndroidSchedulers.mainThread()).
subscribe(new Subscriber<List<UserDto>>() { @Override
public void onSubscribe(Subscription s) { // 观察者接收事件 = 1个
s.request(1);
} @Override
public void onNext(List<UserDto> list) { for (int i = 0; i < list.size(); i++) {
Log.e(TAG, "user:" + list.get(i).toString());
}
} @Override
public void onError(Throwable t) {
} @Override
public void onComplete() {
}
});
}
});
}
}四、注意
需要注意的是，对SQLite的操作是一个耗时的操作，我们需要在子线程中执行，否则将会抛异常。
作者：大熊啊啊啊
链接：https://www.jianshu.com/p/eac17c60be86
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