Room.createFromAsset() 每次打开应用程序时重写应用程序的数据库

Question

当我的应用程序第一次安装时，我正试图从资产数据库初始化它的数据库。然而，在应用程序关闭之前，它一直可以正常工作。当我再次打开应用程序时，它会调用createFromAsset()。据我所知，问题在于我正在获取应用程序数据库的一个实例，并用资产数据库重写它。我只需要在第一次安装应用程序时调用createFromAsset()。

@Database(entities = {ActivitySession.class}, exportSchema = true, version = 1)
public abstract class ActivityPackageDatabase extends RoomDatabase {
private static ActivityPackageDatabase INSTANCE;

public static ActivityPackageDatabase getDatabase(final Context context) {
if (INSTANCE == null) {
synchronized (ActivityPackageDatabase.class) {
if (INSTANCE == null) {
INSTANCE = Room.databaseBuilder(context.getApplicationContext(),
ActivityPackageDatabase.class, "appDB")
.createFromAsset("database/assetDB.db")
.fallbackToDestructiveMigration()
.build();
}
}
}
return INSTANCE;
}

以防万一有实体和DAO 的例子

@Entity
public class SessionPhoto {
@PrimaryKey(autoGenerate = true)
public long id;
public long sessionId;
public String path;
public SessionPhoto() {
}
public long getSessionId() {
return sessionId;
}
public void setSessionId(long sessionId) {
this.sessionId = sessionId;
}
public String getPath() {
return path;
}
public void setPath(String path) {
this.path = path;
}
}

@Dao
public abstract class ActivitySessionDao {
@Update(onConflict = OnConflictStrategy.REPLACE, entity = ActivitySession.class)
public abstract void updateSession(ActivitySession activitySession);
@Insert(onConflict = OnConflictStrategy.REPLACE)
public abstract void addNewJournalEntry(ActivityJournal journalEntry);
@Insert
public abstract long insertSession(ActivitySession activitySession);
@Query("SELECT * FROM activitySession")
public abstract LiveData<List<ActivitySession>> getAllSessionsRecords();
@Transaction
@Query("SELECT * FROM activityPackage WHERE id = :id")
public abstract LiveData<List<ActivityWithSessions>> getActivityWithSessionById(long id);
public  void cancelSession(ActivitySession session){
session.completedDateTime = new Date();
session.status = ActivityPackageStatus.CANCELED;
updateSession(session);
}
@Query("SELECT * FROM activitysession WHERE activityId = :acitivityId AND id = :id")
public abstract ActivitySession findSessionByActivityId(long acitivityId, long id);
}

Answer 1

删除fallbackToDestructiveMigration()。没必要这么说

INSTANCE = Room.databaseBuilder(context.getApplicationContext(),
ActivityPackageDatabase.class, "appDB")
.createFromAsset("database/assetDB.db")
.build();