[移动开发]树莓派提升计划 Android应用用MiniChatAppApp的DB设计与网络模块设计之Room本地数据库

2021SC@SDUSC

Room本地数据库

使用 Room 将数据保存到本地数据库

1.添加依赖

dependencies {
    def room_version = "2.3.0"

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

    // optional - RxJava2 support for Room
    implementation "androidx.room:room-rxjava2:$room_version"

    // optional - RxJava3 support for Room
    implementation "androidx.room:room-rxjava3:$room_version"

    // optional - Guava support for Room, including Optional and ListenableFuture
    implementation "androidx.room:room-guava:$room_version"

    // optional - Test helpers
    testImplementation "androidx.room:room-testing:$room_version"

    // optional - Paging 3 Integration
    implementation "androidx.room:room-paging:2.4.0-beta02"
}

Room 包含 3 个主要组件：

• 数据库：包含数据库持有者，并作为应用已保留的持久关系型数据的底层连接的主要接入点。

  使用?@Database?注释的类应满足以下条件：

  • 是扩展?RoomDatabase?的抽象类。
  • 在注释中添加与数据库关联的实体列表。
  • 包含具有 0 个参数且返回使用?@Dao?注释的类的抽象方法。

  在运行时，您可以通过调用?Room.databaseBuilder()?或?Room.inMemoryDatabaseBuilder()?获取?Database?的实例。

• Entity：表示数据库中的表。

• DAO：包含用于访问数据库的方法。

应用使用 Room 数据库来获取与该数据库关联的数据访问对象 (DAO)。然后，应用使用每个 DAO 从数据库中获取实体，然后再将对这些实体的所有更改保存回数据库中。 最后，应用使用实体来获取和设置与数据库中的表列相对应的值。

Room 不同组件之间的关系如图 1 所示：

图 1.Room 架构图

appdatebase初始化

package com.example.minichatapp.db;

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

import com.example.minichatapp.data.model.Friend;
import com.example.minichatapp.db.dao.FriendDao;
import com.example.minichatapp.db.dao.UserDao;
import com.example.minichatapp.db.model.FriendRoom;
import com.example.minichatapp.db.model.UserRoom;

@Database(entities = {UserRoom.class, FriendRoom.class},version = 1,exportSchema = false)
public abstract class APPDataBase extends RoomDatabase {
    public abstract UserDao userDao();
    public abstract FriendDao friendDao();
}

dao设计

FriendDao.java

package com.example.minichatapp.db.dao;

import androidx.lifecycle.LiveData;
import androidx.lifecycle.MutableLiveData;
import androidx.room.Dao;
import androidx.room.Insert;
import androidx.room.OnConflictStrategy;
import androidx.room.Query;

import com.example.minichatapp.db.model.FriendRoom;

import java.util.List;

import io.reactivex.rxjava3.core.Completable;

@Dao
public interface FriendDao {
    @Query("select * from friend where uid=:uid")
    LiveData<List<FriendRoom>> getFriendsByUId(String uid);

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    Completable insertFriends(List<FriendRoom> roomList);
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    Completable insertFriendOne(FriendRoom friendRoom);
}

UserDao.java

package com.example.minichatapp.db.model;


import androidx.annotation.NonNull;
import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.PrimaryKey;


@Entity(tableName = "user")
public class UserRoom {
    @PrimaryKey
    @ColumnInfo(name = "uid")
    @NonNull
    public String  uid = null;
    @ColumnInfo(name = "user_name")
    public String userName;
    @ColumnInfo(name = "is_log")
    public int isLog;

    @Override
    public String toString() {
        return "UserRoom{" +
                "uid='" + uid + '\'' +
                ", userName='" + userName + '\'' +
                ", isLog=" + isLog +
                '}';
    }
}

3.表设计

UserRoom.java

package com.example.minichatapp.db.model;


import androidx.annotation.NonNull;
import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.PrimaryKey;


@Entity(tableName = "user")
public class UserRoom {
    @PrimaryKey
    @ColumnInfo(name = "uid")
    @NonNull
    public String  uid = null;
    @ColumnInfo(name = "user_name")
    public String userName;
    @ColumnInfo(name = "is_log")
    public int isLog;

    @Override
    public String toString() {
        return "UserRoom{" +
                "uid='" + uid + '\'' +
                ", userName='" + userName + '\'' +
                ", isLog=" + isLog +
                '}';
    }
}

FriendRoom.java

package com.example.minichatapp.db.model;

import androidx.annotation.NonNull;
import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.PrimaryKey;

@Entity(tableName = "friend",primaryKeys = {"fid","uid"})
public class FriendRoom {

    @ColumnInfo(name = "fid")
    @NonNull
    public String fid="-1";
    @ColumnInfo(name = "uid")
    @NonNull
    public String uid="-1";
    @ColumnInfo(name = "f_name")
    public String f_name;
    @ColumnInfo(name = "nick_name")
    public String nick_name;

    public FriendRoom(@NonNull String fid, @NonNull String uid, String f_name, String nick_name) {
        this.fid = fid;
        this.uid = uid;
        this.f_name = f_name;
        this.nick_name = nick_name;
    }
}