Architecture Components（2）初识Room

项目地址https://github.com/gms76575/simplearch2.git

介绍

Room是Google提供的一个ORM库。Room是一个数据持久化库，它是 Architecture Component的一部分。它让SQLiteDatabase的使用变得简单，大大减少了重复的代码，并且把SQL查询的检查放在了编译时。Room提供了三个主要的组件：

1. @Database：@Database用来注解类，并且注解的类必须是继承自RoomDatabase的抽象类。该类主要作用是创建数据库和创建Daos（data access objects，数据访问对象）。
2. @Entity：@Entity用来注解实体类，@Database通过entities属性引用被@Entity注解的类，并利用该类的所有字段作为表的列名来创建表。
3. @Dao：@Dao用来注解一个接口或者抽象方法，该类的作用是提供访问数据库的方法。在使用@Database注解的类中必须定一个不带参数的方法，这个方法返回使用@Dao注解的类。

使用

User.java

@Entity(tableName = "user")
public class UserEntity implements User
{
    @NonNull
    @PrimaryKey
    private String uid;
    private String name;
    private String phone;
    private int gender;
    @ColumnInfo(name = "update_at")
    private Date updateAt;
    ...
    public UserEntity(@NonNull String uid, String name, String phone, int gender, Date update)
    {
        ...
    }

    //如果有多个构造方法，使用 @Ignore注解告诉Room哪个用，哪个不用。
    @Ignore
    public UserEntity(User user)
    {
        ...
    }

dao

@Dao
public interface UserDao
{
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void insertOrUpdate(UserEntity user);

    @Query("select uid,name,phone,gender,update_at from user where uid=:uid")
    LiveData<UserEntity> getUserInfo(String uid);

    @Query("select count(uid) from user where uid=:uid and date('now') - update_at<:outTime")
    int notOutTime(String uid, long outTime);
}

database

@Database(entities = {UserEntity.class}, version = 1, exportSchema = false)
@TypeConverters(DateConverter.class)
public abstract class AppDatabase extends RoomDatabase {
    //每次创建AppDatabase实例都会产生比较大的开销，所以应该将AppDatabase设计成单例的。
    private static AppDatabase sInstance;

    @VisibleForTesting
    public static final String DATABASE_NAME = "basic-sample-db";

    public abstract UserDao userDao();

    private final MutableLiveData<Boolean> mIsDatabaseCreated = new MutableLiveData<>();

    public static AppDatabase getInstance(final Context context, final AppExecutors executors) {
        if (sInstance == null) {
            synchronized (AppDatabase.class) {
                if (sInstance == null) {
                    sInstance = buildDatabase(context.getApplicationContext(), executors);
                    sInstance.updateDatabaseCreated(context.getApplicationContext());
                }
            }
        }
        return sInstance;
    }

    private static AppDatabase buildDatabase(final Context appContext,
                                             final AppExecutors executors) {
        return Room.databaseBuilder(appContext, AppDatabase.class, DATABASE_NAME)
                .addCallback(new Callback() {
                    @Override
                    public void onCreate(@NonNull SupportSQLiteDatabase db) {
                        super.onCreate(db);
                        AppDatabase database = AppDatabase.getInstance(appContext, executors);
                        database.setDatabaseCreated();
                    }
                }).build();
    }

    private void updateDatabaseCreated(final Context context) {
        if (context.getDatabasePath(DATABASE_NAME).exists()) {
            setDatabaseCreated();
        }
    }

    private void setDatabaseCreated(){
        mIsDatabaseCreated.postValue(true);
    }

    public LiveData<Boolean> getDatabaseCreated() {
        return mIsDatabaseCreated;
    }
}

repository

public class DataRepository {

    private static DataRepository sInstance;

    private final AppDatabase mDatabase;

    private DataRepository(final AppDatabase database) {
        mDatabase = database;
    }

    public static DataRepository getInstance(final AppDatabase database) {
        if (sInstance == null) {
            synchronized (DataRepository.class) {
                if (sInstance == null) {
                    sInstance = new DataRepository(database);
                }
            }
        }
        return sInstance;
    }

    public void insertOrUpdate(UserEntity user){
        mDatabase.userDao().insertOrUpdate(user);
    }

    public LiveData<UserEntity> getUserInfo(String uid){
        return mDatabase.userDao().getUserInfo(uid);
    }

    public boolean notOutTime(String uid, long outTime){
        return mDatabase.userDao().notOutTime(uid, outTime)>0;
    }

}

application

public class BasicApp extends Application
{

    private AppExecutors mAppExecutors;

    @Override
    public void onCreate() {
        super.onCreate();

        mAppExecutors = new AppExecutors();
    }

    public AppDatabase getDatabase() {
        return AppDatabase.getInstance(this, mAppExecutors);
    }

    public DataRepository getRepository() {
        return DataRepository.getInstance(getDatabase());
    }
}

ui

LoginActiviy.java

@Override
        protected Boolean doInBackground(Void... params)
        {
            try
            {
                // Simulate network access.
                UserEntity user = new UserEntity(UUID.randomUUID().toString(),"zhangquandan",mPhone,1,new Date(System.currentTimeMillis()));
                ((BasicApp)getApplication()).getRepository().insertOrUpdate(user);
                SharedPreferences sp = getSharedPreferences("pet", MODE_PRIVATE);
                sp.edit().putString("uid", user.getUid()).apply();
                Thread.sleep(2000);
            }
            catch (InterruptedException e)
            {
                return false;
            }

            return "000000".equals(mPassword);
        }

MyFragment.java

public class MyFragment extends Fragment implements LifecycleOwner
{

    private FragmentMyBinding mBinding;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState)
    {
        mBinding = DataBindingUtil.inflate(inflater, R.layout.fragment_my, container, false);
        return mBinding.getRoot();
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState)
    {
        super.onViewCreated(view, savedInstanceState);
        SharedPreferences sp = getActivity().getSharedPreferences("pet", Activity.MODE_PRIVATE);
        ((BasicApp)getActivity().getApplication()).getRepository().getUserInfo(sp.getString("uid", ""))
        .observe(this,user->mBinding.setMy(user));
    }
}

项目地址https://github.com/gms76575/simplearch2.git

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