Android room数据库使用详解

1、引入库

 def room_version = "2.3.0"
    implementation "androidx.room:room-runtime:$room_version"
    // for kotlin use kapt instead of annotationprocessor
    annotationprocessor "androidx.room:room-compiler:$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"

2.appdatabase类

@database(entities = {
        //用户信息
        userinfo.class
        }, version = 1, exportschema = false)
public abstract class appdatabase extends roomdatabase {
    private static appdatabase instance;
 
    public static synchronized appdatabase getinstance(context context) {
        if (instance == null) {
            instance = room.databasebuilder(context, appdatabase.class, 
                      //数据库存放在sd卡
                     fileutils.getdatabasepath("test.db"))
                    //.addmigrations(migration_1_2)
                    .build();
        }
        return instance;
    }
 
    public abstract roomdao roomdao();
 
    //进行数据库升级
    static final migration migration_1_2 = new migration(1, 2) {
        @override
        public void migrate(@nonnull supportsqlitedatabase database) {
            //在这里用sql脚本完成
            database.execsql("alter table user add column flag integer not null default 1");
        }
    };
}

public class fileutils {
 
    public static void deletefile(string filename) {
        file file = new file(filename);
        if (file.exists())
            file.delete();
    }
 
    /**
     * 获得数据库路径，如果不存在，则创建对象对象
     *
     * @param name
     */
    public static string getdatabasepath(string name) {
        //判断是否存在sd卡
        boolean sdexist = android.os.environment.media_mounted.equals(android.os.environment.getexternalstoragestate());
        if (!sdexist) {//如果不存在,
            log.e("sd卡管理：", "sd卡不存在，请加载sd卡");
            return null;
        } else {//如果存在
            //获取sd卡路径
            string dbdir = android.os.environment.getexternalstoragedirectory().getabsolutepath();
            dbdir += "/database";//数据库所在目录
            string dbpath = dbdir + "/" + name;//数据库路径
            logutil.d("dbpath:" + dbpath);
            return dbpath;
        }
    }
}

3.用户表

@entity(tablename = "user")
public class userinfo extends basebean {
    @nonnull
    @primarykey
    private string userid;
    private string name;//用户名
    private string headimg;
    private string pwd;
    private string createtime;
    @ignore
    private boolean isselect;
 
    public userinfo() {
    }
 
    @ignore
    public userinfo(string userid, string name, string headimg, string pwd) {
        this.userid = userid;
        this.name = name;
        this.headimg = headimg;
        this.pwd = pwd;
    }
 
 
    public string getuserid() {
        return userid;
    }
 
    public void setuserid(string userid) {
        this.userid = userid;
    }
 
    public string getname() {
        return name;
    }
 
    public void setname(string name) {
        this.name = name;
    }
 
 
    public string getheadimg() {
        return headimg;
    }
 
    public void setheadimg(string headimg) {
        this.headimg = headimg;
    }
 
    public string getpwd() {
        return pwd;
    }
 
    public void setpwd(string pwd) {
        this.pwd = pwd;
    }
 
    public boolean isselect() {
        return isselect;
    }
 
    public void setselect(boolean select) {
        isselect = select;
    }
 
    public string getcreatetime() {
        return createtime;
    }
 
    public void setcreatetime(string createtime) {
        this.createtime = createtime;
    }
}

4.roomdao

@dao
public interface roomdao {
    /**
     * 插入用户
     *
     * @param user
     */
    @insert
    void insertuser(userinfo user);
 
    //如果插入的新数据在表中已经存在，即如果遇上数据冲突的情况，新数据直接替换旧数据；
    @insert(onconflict = onconflictstrategy.replace)
    void insertuser(userinfo... user);
 
    @update
    void updateuser(userinfo note);
 
    /**
     * 获取所有的用户
     *
     * @return
     */
    @query("select * from user")
    livedata<list<userinfo>> getuserlist();
 
    /**
     * 根据用户名查询用户
     *
     * @param username
     * @return
     *
    @query("select * from user where name = :username limit 1")
    livedata<userinfo> finduserbyname(string username);
    /**
     * 根据userid查询用户
     */
    @query("select * from user where userid = :userid limit 1")
    livedata<userinfo> finduserbyid(string userid);
}

5.repository 

public class repository {
 
    private final appdatabase appdb;
 
    public repository(context context) {
        appdb = appdatabase.getinstance(context);
    }
 
    /**
     * 插入用户
     *
     * @param user
     */
    public void insertuser(final userinfo user) {
        new asynctask<void, void, void>() {
            @override
            protected void doinbackground(void... voids) {
                appdb.roomdao().insertuser(user);
                return null;
            }
        }.execute();
    }
 
    /**
     * 获取所有的用户信息
     *
     * @return
     */
    public livedata<list<userinfo>> getuserlist() {
        return appdb.roomdao().getuserlist();
    }
 
    /**
     * 根据用户名查询用户
     */
    public livedata<userinfo> finduserbyname(string name) {
        return appdb.roomdao().finduserbyname(name);
    }
 
    /**
     * 根据userid查询用户
     */
    public livedata<userinfo> finduserbyid(string userid) {
        return appdb.roomdao().finduserbyid(userid);
    }
}

6.使用

repository repository = new repository(context);
 
 repository.getuserlist().observe(this, new observer<list<userinfo>>() {
            @override
            public void onchanged(list<userinfo> userlist) {
                muserlist = userlist;
                logutil.d("muserlist个数：" + muserlist.size());
                if (muserlist.size() > 0) {
                    madapter.setlist(userlist);
                }
            }
        });

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