最近博主把一个以前用原生数据库写的单词APP中数据库部分改成了room，在这个过程中踩了很多坑
坑大概为两点
- 使用room增删改查的一些语句
- 导入外部数据库并对其表格内容进行增删改查
在项目最后是全部重构成功了，但是在处理外部数据库时遇到的坑比较多，一时间没整理出来（整理了一个demo，但是没整理完），所以这篇文章解决room增删改查的一些常用语句。
如果项目吃急，遇到外部数据库的一些问题，可通过公众号：计蒙不吃鱼 联系博主
相信看这篇文章的人应该都有room的使用基础了，所以直接上菜（以下图表格为例）。
如上图：表名为forget
- 单词名称：wordname
- 单词等级：wordclass
- 单词时间：wordtime
插入数据（增）：
//Forget为表的实体类
@Insert
void insertWords(Forget... forgets);
删除数据（删）：
//1.删除数据，根据主键来删除数据的！！！
@Delete
void deleteWords(Forget... forgets);
//2.根据单词名称删除表中数据（单个）
@Query("DELETE FROM FORGET where wordname=:name")
void deleteWords(String name);
//3.根据单词名称，单词等级删除表中数据（多个）
@Query("DELETE FROM FORGET where wordname=:name and wordclass=:wordclass")
void deleteWords(String name，String wordclass);
更新数据（改）：
//更新数据
@Update
void updateWords(Forget... forgets);
//根据单词名称修改单词等级
@Query("UPDATE FORGET SET wordclass= :wordclasss WHERE wordname = :wordname")
void updateWords(String wordname,String wordclasss);
查询数据（查）：
//查询全部数据
@Query(" SELECT * FROM FORGET ORDER BY rowid DESC")
LiveData<List<Forget>> getAllForgetLive();
//查询某项的全部数据
@Query(" SELECT wordname FROM FORGET")
LiveData<List<Forget>> getAllForgetLive();
//查询表中某单词是否存在 存在返回值为1，不存在返回值为0.
@Query("select 1 from forget where wordname =:wordname limit 1")
int forgetWordisExist(String wordname);
//部分查询 大多用于分页加载
@Query(" SELECT wordname,wordclass,wordtime FROM FORGET limit :start,:end")
LiveData<List<Forget>> getHarfWordsLive(int start,int end);
//根据单词名称得到此行的全部信息
@Query("SELECT * FROM FORGET WHERE wordname= :name")
Forget getForgetByName(String name);
Forget实体类如下
@Fts4
@Entity(tableName = "forget")
public class Forget {
@Ignore
@PrimaryKey(autoGenerate = true)
private int rowid;
@ColumnInfo(name="wordname")
private String wordname;
@ColumnInfo(name="wordclass")
private String wordclass;
@ColumnInfo(name="wordtime")
private String wordtime;
public String getWordname() {
return wordname;
}
public void setWordname(String wordname) {
this.wordname = wordname;
}
public String getWordclass() {
return wordclass;
}
public void setWordclass(String wordclass) {
this.wordclass = wordclass;
}
public String getWordtime() {
return wordtime;
}
public void setWordtime(String wordtime) {
this.wordtime = wordtime;
}
public Forget(String wordname, String wordclass, String wordtime) {
this.wordname = wordname;
this.wordclass = wordclass;
this.wordtime = wordtime;
}
}
Dao文件如下：
@Dao //访问数据库的一个接口
public interface WordDao {
@Insert
void insertWords(Forget... forgets);
//根据单词名称删除表中数据
@Query("DELETE FROM FORGET where wordname=:name")
void deleteWords(String name);
//根据单词名称更新表中数据
@Query("UPDATE FORGET SET wordclass= :wordclasss WHERE wordname = :wordname")
void updateWords(String wordname,String wordclasss);
//查询表中某数据是否存在
@Query("select 1 from forget where wordname =:wordname limit 1")
int forgetWordisExist(String wordname);
//分页加载：
@Query(" SELECT example,english,phonetic,chinese FROM FOURS limit :start,:end")
LiveData<List<Word>> getHarfWordsLive(int start,int end);
//查询全部
@Query(" SELECT * FROM FORGET ORDER BY rowid DESC")
LiveData<List<Forget>> getAllForgetLive();
//根据字段查询
@Query("SELECT * FROM FORGET WHERE wordname= :name")
Forget getForgetByName(String name);
}
DataBase文件如下
@Database(entities = {
Forget.class},version =1,exportSchema = false)
public abstract class WordDataBase extends RoomDatabase {
private static WordDataBase INSTANCE;
static synchronized WordDataBase getDatabase(final Context context){
if (INSTANCE==null){
INSTANCE= Room.databaseBuilder(context.getApplicationContext(),WordDataBase.class,"word.db")
.createFromAsset("word.db") //预填充数据库
.fallbackToDestructiveMigration()
.build();
}
return INSTANCE;
}
public abstract WordDao getWordDao();
}
Repository文件如下
class WordRepository {
private LiveData<List<Forget>> allForgetLive;
private WordDao wordDao;
private WordDataBase wordDatabase;
WordRepository(Context context){
//单例
wordDatabase=WordDataBase.getDatabase(context.getApplicationContext());
allForgetLive=wordDao.getAllForgetLive();
}
public LiveData<List<Forget>> getAllForgetLive() {
return allForgetLive;
}
public Forget getForgetByName(String name) {
return wordDao.getForgetByName(name);
}
public int forgetWordisExist(final String wordname){
return wordDao.forgetWordisExist(wordname);
}
void insertWords(final Forget...forgets){
RxBusMax.getInstance().chainProcess(new Func1() {
@Override
public Object call(Object o) {
wordDao.insertWords(forgets);
return null;
}
});
}
void deleteWords(final String name){
RxBusMax.getInstance().chainProcess(new Func1() {
@Override
public Object call(Object o) {
wordDao.deleteWords(name);
return null;
}
});
}
void updateWords(final String wordname,final String wordclass){
RxBusMax.getInstance().chainProcess(new Func1() {
@Override
public Object call(Object o) {
wordDao.updateWords(wordname,wordclass);
return null;
}
});
}
}
ViewMode文件如下
public class WordViewModel extends AndroidViewModel {
private WordRepository wordRepository;
public WordViewModel(@NonNull Application application) {
super(application);
//单例
wordRepository=new WordRepository(application);
}
public LiveData<List<Forget>> getAllForgetLive() {
return wordRepository.getAllForgetLive();
}
public void insertWords(Forget...forgets){
wordRepository.insertWords(forgets);
}
public void deleteWords(String name){
wordRepository.deleteWords(name);
}
public Forget getForgetByName(String name) {
return wordRepository.getForgetByName(name);
}
public void updateWords(String wordname,String wordclasss){
wordRepository.updateWords(wordname,wordclasss);
}
public int forgetWordisExist(final String wordname){
return wordRepository.forgetWordisExist(wordname);
}
public LiveData<List<Word>> getHalfWordsLive(int start,int end) {
return wordRepository.getHalfwordLive(start,end);
}
}