ROOM
ROOM对Sqlite进行了封装，直接使用ROOM来进行数据库访问。
代码：https://github.com/Gong-Shijie/RoomDemo
ROOM数据库查询可以直接返回LiveData对象，每次CRUD都会自动更新该LiveData，LiveData始终是数据库最新值
利用该特性可以直接将数据库的变化，通过LiveData作为观察者传递到ViewModel，保证拿到的数据都是数据库中时刻最新的值
使用流程：
Entry类-->Dao-->EntryRoomDatabase(单例模式)-->Repository(从EntryRoomDatabase获得Dao)-->在Repository中实现异步-->AndroidViewModel通过Repository访问数据库CRUD
框架
数据库操作不应该在MainThread中，所以我们使用AsyncTask来进行数据库操作。
详细设计
UI层（Activity和Fragment）所有的数据应该都直接从ViewModel来获取，在ViewModel中我们使用AsyncTask来进行数据库操作。
ROOM进行数据库操作依赖于Dao接口，在该接口中实现了很多数据库操作。
主要角色
- Entry 实体类
- Dao 定义接口数据库操作
- 继承RoomDatabase 通过ROOM实例化database返回Dao供调用
- 异步类调用Dao中数据库操作如AsyncTask
- Repository对操作进行封装
- AndroidViewModel 聚合 Repository来执行数据库操作
使用方法
工程结构
Entry类-->Dao-->EntryRoomDatabase(单例模式)-->Repository(从EntryRoomDatabase获得Dao)-->在Repository中实现异步-->AndroidViewModel通过Repository访问数据库CRUD
代码实现
Entry
@Entity
public class Word {
@PrimaryKey(autoGenerate = true)
private int id;
@ColumnInfo(name = "english")
private String english;
@ColumnInfo(name = "chinese")
private String mean;
public Word(String english, String mean) {
this.english = english;
this.mean = mean;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getEnglish() {
return english;
}
public void setEnglish(String english) {
this.english = english;
}
public String getMean() {
return mean;
}
public void setMean(String mean) {
this.mean = mean;
}
}
Dao
@Dao
public interface WordDao {
@Insert
void insertWord(Word... words);
@Update
void update(Word... words);
@Delete
void delete(Word... words);
@Query("DELETE FROM WORD")
void deleteAll();
@Query("SELECT * FROM WORD ORDER BY ID DESC")
LiveData<List<Word>> getAll();
}
WordRoomDatabase
@Database(entities = {Word.class},version = 1,exportSchema = false)
public abstract class WordRoomDatabase extends RoomDatabase {
public abstract WordDao getWordDao();
private static WordRoomDatabase INSTANCE;
public static WordRoomDatabase getInstance(final Context context) {
if (INSTANCE == null) {
synchronized (WordRoomDatabase.class) {
if (INSTANCE == null) {
INSTANCE = Room.databaseBuilder(context.getApplicationContext(),
WordRoomDatabase.class, "word_database")
.build();
}
}
}
return INSTANCE;
}
}
Repository
public class Repository {
private LiveData<List<Word>> wordsLive;
public LiveData<List<Word>> getWordsLive() {
return wordsLive;
}
//用来调用数据库操作
private WordDao wordDao;
public Repository(Context context) {
WordRoomDatabase wordRoomDatabase = WordRoomDatabase.getInstance(context.getApplicationContext());
wordDao = wordRoomDatabase.getWordDao();
wordsLive = wordDao.getAll();
}
public void insert(Word... words){
new InsertTask(wordDao).execute(words);
}
public void delete(Word... words){
new DeleteTask(wordDao).execute(words);
}
public void update(Word... words){
new UpdateTask(wordDao).execute(words);
}
public void deleteAll(){
new DeleteAllTask(wordDao).execute();
}
}
VeiwModel
public class MainViewModel extends AndroidViewModel {
// ViewModel 没有很好的方法来获得一个Context 需要继承AndroidViewModel
Repository repository;
public MainViewModel(Application application) {
super(application);
this.repository = new Repository(application);
}
public LiveData<List<Word>> getAll(){
return repository.getWordsLive();
}
public void insert(Word... words){
repository.insert(words);
}
public void update(Word... words){
repository.update(words);
}
public void delete(Word... words){
repository.delete(words);
}
public void deleteAll(){
repository.deleteAll();
}
}
总结
总结
