Android JetPack之ROOM(三)

前面两篇已经把用户表和群组表创建完成，由于一个群组包含多个用户，一个用户拥有多个群组，所以他们是多对多的关系。ROOM数据库除了支持多对多的关系，还支持一对多，一对一的关系。可以使用Relation关键字处理。

• 注意：一对一的关系是2.2.0版本开始支持，之前的版本不支持，另外文档没有写这回事，只有版本更新里面提到过这个事情。

由于群组和用户的多对多关系，所以需要创建中间表用来保存他们的关系，中间表结构如下：

中间关系表

package com.room.test.model;


import androidx.annotation.NonNull;
import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.ForeignKey;
import androidx.room.Index;

/**
 * 多对多关系中，需要使用索引，为了避免警告，同时也是为了提高查询效率
 */

@Entity(tableName = "team_user_join",
        primaryKeys = { "teamId","userId"},
        foreignKeys = {@ForeignKey(entity = TeamModel.class,
                parentColumns = "teamId",
                childColumns = "teamId"),
                @ForeignKey(entity = UserModel.class,
                        parentColumns = "userId",
                        childColumns = "userId")
        },indices = {@Index(value = "teamId",unique = true),@Index(value = "userId",unique = true)})
public class TeamUserJoinModel {
    @ColumnInfo(name = "teamId")
    @NonNull
    private String teamId;

    @ColumnInfo(name = "userId")
    @NonNull
    private String userId = "";

    @NonNull
    public String getTeamId() {
        return teamId;
    }

    public void setTeamId(@NonNull String teamId) {
        this.teamId = teamId;
    }

    @NonNull
    public String getUserId() {
        return userId;
    }

    public void setUserId(@NonNull String userId) {
        this.userId = userId;
    }
}

数据操作接口（DAO类）

package com.room.test.dao;

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

import com.room.test.model.TeamModel;
import com.room.test.model.UserModel;
import com.room.test.model.TeamUserJoinModel;

import java.util.List;

@Dao
public interface TeamUserJoinDao {
    /**
     * 多对多的关系查询中，如果返回所有数据时候，会返回额外的字段(作为条件查询的字段)，这时候会出现警告，解决警告的方式有两种
     * 1、返回确定的字段
     * 2、采用注解，本例使用的该方式
     * 如果不是多对多的关系，那么可能是映射的字段写错了。
     */
    @SuppressWarnings(RoomWarnings.CURSOR_MISMATCH)
    @Query("SELECT * FROM user_table INNER JOIN team_user_join ON team_user_join.userId = user_table.userId WHERE team_user_join.teamId = :teamId")
    LiveData<List<UserModel>> getAlphabetizedUser(String teamId);

    @Insert(onConflict = OnConflictStrategy.IGNORE)
    void insert(TeamUserJoinModel word);

    @Insert
    void insert(List<TeamUserJoinModel> playlistSongJoinList);

    @SuppressWarnings(RoomWarnings.CURSOR_MISMATCH)
    @Query("SELECT * FROM team_table " +
            "INNER JOIN team_user_join " +
            "ON team_table.teamId = team_user_join.teamId " +
            "WHERE team_user_join.userId = :userId")
    LiveData<List<TeamModel>> getTeamForUser(String userId);

}

数据库

package com.room.test.db;

import android.content.Context;
import android.text.TextUtils;

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

import com.room.test.dao.TeamUserJoinDao;
import com.room.test.dao.UserDao;
import com.room.test.dao.TeamDao;
import com.room.test.model.UserModel;
import com.room.test.model.TeamModel;
import com.room.test.model.TeamUserJoinModel;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

@Database(entities = {
        TeamUserJoinModel.class,
        UserModel.class,
        TeamModel.class},
        version = 1, exportSchema = false)

public abstract class UserDatabase extends RoomDatabase {
    public abstract TeamDao userDao();

    public abstract UserDao cardDao();

    public abstract TeamUserJoinDao userCardJoinDao();

    private static volatile UserDatabase INSTANCE;
    private static final int NUMBER_OF_THREADS = 4;
    public static final ExecutorService databaseWriteExecutor =
            Executors.newFixedThreadPool(NUMBER_OF_THREADS);

    public static UserDatabase getDatabase(final Context context) {
        if (INSTANCE == null) {
            synchronized (UserDatabase.class) {
                if (INSTANCE == null) {
                    INSTANCE = Room.databaseBuilder(context.getApplicationContext(),
                            UserDatabase.class, "user_database")//数据库名
                            .build();
                }
            }
        }
        return INSTANCE;
    }
}

中心仓库

package com.room.test.repository;

import android.app.Application;

import androidx.lifecycle.LiveData;

import com.room.test.dao.TeamUserJoinDao;
import com.room.test.db.UserDatabase;
import com.room.test.model.TeamUserJoinModel;
import com.room.test.model.UserModel;

import java.util.List;

public class TeamCardRepository {
    private TeamUserJoinDao uCardDao;
    private LiveData<List<UserModel>> mAllUser;
    public TeamCardRepository(Application application) {
        UserDatabase db = UserDatabase.getDatabase(application);
        uCardDao = db.userCardJoinDao();
    }


    public LiveData<List<UserModel>> getUserForTeam(String teamId) {
        return uCardDao.getAlphabetizedUser(teamId);
    }

    public void insert(final TeamUserJoinModel user) {
        UserDatabase.databaseWriteExecutor.execute(new Runnable() {
            @Override
            public void run() {
                uCardDao.insert(user);
            }
        });
    }

}

数据处理中心

package com.room.test.viewmodel;

import android.app.Application;

import androidx.annotation.NonNull;
import androidx.lifecycle.AndroidViewModel;
import androidx.lifecycle.LiveData;

import com.room.test.model.TeamUserJoinModel;
import com.room.test.model.UserModel;
import com.room.test.repository.TeamCardRepository;

import java.util.List;

public class TeamCardViewModel extends AndroidViewModel{
    private TeamCardRepository mRepository;

    public TeamCardViewModel(@NonNull Application application) {
        super(application);
        mRepository = new TeamCardRepository(application);
    }

    public LiveData<List<UserModel>> getUserForTeam(String teamId) {
        return mRepository.getUserForTeam(teamId);
    }

    public void insert(TeamUserJoinModel user) { mRepository.insert(user); }

}

ROOM版本更新记录： https://developer.android.com/jetpack/androidx/releases/room