请在构建器中提供迁移或在构建器中调用 fallbackToDestructiveMigration，在这种情况下 Room 将重新创建所有表

Question

我正在使用带有 RxJava2 的 Room。我在 table 中添加了一列，因此我正在迁移到新版本。我已将我的数据库版本更改为 2。

以下是我的迁移代码

static final Migration MIGRATION_1_2 = new Migration(1, 2) {
    @Override
    public void migrate(SupportSQLiteDatabase database) {
        database.execSQL("ALTER TABLE users "
        +"ADD COLUMN address String");

    }
};

AppDatabase db = Room.databaseBuilder(getApplicationContext(), AppDatabase.class, DB_NAME)
.addMigrations(MIGRATION_1_2)
.build();

如果您想查看完整代码，我指的是 Github 上的这个例子，它没有迁移代码

https://github.com/alahammad/RoomSample

我正在按照文档中描述的步骤进行操作，但我的应用程序仍然崩溃。

错误日志

Process: demo.karaoke.sensibol.com.roomrajava2, PID: 13655
    io.reactivex.exceptions.OnErrorNotImplementedException: A migration from 1 to 2 is necessary. Please provide a Migration in the builder or call fallbackToDestructiveMigration in the builder in which case Room will re-create all of the tables.
        at io.reactivex.internal.functions.Functions$OnErrorMissingConsumer.accept(Functions.java:704)
        at io.reactivex.internal.functions.Functions$OnErrorMissingConsumer.accept(Functions.java:701)
        at io.reactivex.internal.operators.maybe.MaybeCallbackObserver.onError(MaybeCallbackObserver.java:83)
        at io.reactivex.internal.operators.maybe.MaybeObserveOn$ObserveOnMaybeObserver.run(MaybeObserveOn.java:99)
        at io.reactivex.android.schedulers.HandlerScheduler$ScheduledRunnable.run(HandlerScheduler.java:109)
        at android.os.Handler.handleCallback(Handler.java:815)
        at android.os.Handler.dispatchMessage(Handler.java:104)
        at android.os.Looper.loop(Looper.java:194)
        at android.app.ActivityThread.main(ActivityThread.java:5643)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:960)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
     Caused by: java.lang.IllegalStateException: A migration from 1 to 2 is necessary. Please provide a Migration in the builder or call fallbackToDestructiveMigration in the builder in which case Room will re-create all of the tables.
        at android.arch.persistence.room.RoomOpenHelper.onUpgrade(RoomOpenHelper.java:82)
        at android.arch.persistence.db.framework.FrameworkSQLiteOpenHelper$OpenHelper.onUpgrade(FrameworkSQLiteOpenHelper.java:118)
        at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:256)
        at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:163)
        at android.arch.persistence.db.framework.FrameworkSQLiteOpenHelper$OpenHelper.getWritableSupportDatabase(FrameworkSQLiteOpenHelper.java:93)
        at android.arch.persistence.db.framework.FrameworkSQLiteOpenHelper.getWritableDatabase(FrameworkSQLiteOpenHelper.java:54)
        at android.arch.persistence.room.RoomDatabase.query(RoomDatabase.java:193)
        at demo.karaoke.sensibol.com.roomrajava2.UserDao_Impl.call(UserDao_Impl.java:137)
        at demo.karaoke.sensibol.com.roomrajava2.UserDao_Impl.call(UserDao_Impl.java:135)
        at io.reactivex.internal.operators.maybe.MaybeFromCallable.subscribeActual(MaybeFromCallable.java:46)
        at io.reactivex.Maybe.subscribe(Maybe.java:3749)
        at io.reactivex.internal.operators.maybe.MaybeSubscribeOn$SubscribeTask.run(MaybeSubscribeOn.java:54)
        at io.reactivex.Scheduler$DisposeTask.run(Scheduler.java:452)
        at io.reactivex.internal.schedulers.ScheduledRunnable.run(ScheduledRunnable.java:66)
        at io.reactivex.internal.schedulers.ScheduledRunnable.call(ScheduledRunnable.java:57)
        at java.util.concurrent.FutureTask.run(FutureTask.java:237)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access1(ScheduledThreadPoolExecutor.java:152)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:265)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
        at java.lang.Thread.run(Thread.java:818)

Answer 1

我运行你的应用程序来自 GitHub 并做了一个从版本 1 到版本 2 的示例迁移。结果 SQL 查询中有一个错误。应该是：

static final Migration MIGRATION_1_2 = new Migration(1, 2) {
    @Override
    public void migrate(SupportSQLiteDatabase database) {
        database.execSQL("ALTER TABLE users "
        +"ADD COLUMN address TEXT");

    }
};

字符串 > 文本

最好将 Room 的数据库实例设为单例，并且仅在 Repo/CacheManager class 中使用它。请检查要点以获得完整的代码更改 - https://gist.github.com/lomza/0f311a1b1e9c896bc58dff925d65eab2

Answer 2

在 build() 之前添加“.fallbackToDestructiveMigration()”，

Answer 3

如果您不想提供迁移，并且特别希望在升级版本时清除数据库，请在数据库构建器中调用 fallbackToDestructiveMigration

database = Room.databaseBuilder(context.getApplicationContext(),
                    UsersDatabase.class, "Sample.db")
            .fallbackToDestructiveMigration()
            .build();

Answer 4

如果可以接受丢失现有数据，请在创建数据库时调用 fallbackToDestructiveMigration() 构建器方法

示例：

db = Room.databaseBuilder(getApplicationContext(),
                    User.class, "DB_Name")
            .fallbackToDestructiveMigration()
            .build();

Answer 5

在 build() 之前添加“.fallbackToDestructiveMigration()”，并且还增加了为我修复的版本号。希望它能为搜索的人修复。这里。

请在构建器中提供迁移或在构建器中调用 fallbackToDestructiveMigration，在这种情况下 Room 将重新创建所有表

Please provide a Migration in the builder or call fallbackToDestructiveMigration in the builder in which case Room will re-create all of the tables

android

android-room