Room数据库新增列报错：计算数据库LiveData时发生异常的原因及解决方案

我定义了包含requirePolice布尔字段的Crime数据类：

@Entity
data class Crime(
    @PrimaryKey val id : UUID = UUID.randomUUID(),
    var title: String = "",
    var date: Date = Date(),
    var isSolved: Boolean = false,
    var requirePolice : Boolean = false, // 新增布尔字段
    var suspect: String = ""
){
    val photoFileName get() = "IMG_$id.jpg"
}

将数据库版本从2升级到3并添加迁移：

@Database(entities = [Crime::class], version = 3)
@TypeConverters(CrimeTypeConverters::class)
abstract class CrimeDatabase: RoomDatabase(){
    abstract fun crimeDao() : CrimeDao
}

val migration_1_2 = object : Migration(1,2){
    override fun migrate(database: SupportSQLiteDatabase) {
        database.execSQL("ALTER TABLE Crime ADD COLUMN suspect TEXT NOT NULL DEFAULT ''")
    }
}

val migration_2_3 = object : Migration(2,3){
    override fun migrate(database: SupportSQLiteDatabase) {
        database.execSQL("ALTER TABLE Crime ADD COLUMN requirePolice TEXT NOT NULL DEFAULT ''")
    }
}

在Repository中配置迁移后，运行时出现崩溃，错误日志如下：

E/AndroidRuntime: FATAL EXCEPTION: arch_disk_io_0
Process: com.bignerdranch.android.criminalintent, PID: 22566
java.lang.RuntimeException: Exception while computing database live data.
    at androidx.room.RoomTrackingLiveData$1.run(RoomTrackingLiveData.java:92)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
    at java.lang.Thread.run(Thread.java:923)
Caused by: java.lang.IllegalStateException: Migration didn't properly handle: Crime(com.bignerdranch.android.criminalintent.Crime).
Expected:
TableInfo{name='Crime', columns={date=Column{name='date', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=0, defaultValue='null'}, requirePolice=Column{name='requirePolice', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=0, defaultValue='null'}, id=Column{name='id', type='TEXT', affinity='2', notNull=true, primaryKeyPosition=1, defaultValue='null'}, suspect=Column{name='suspect', type='TEXT', affinity='2', notNull=true, primaryKeyPosition=0, defaultValue='null'}, title=Column{name='title', type='TEXT', affinity='2', notNull=true, primaryKeyPosition=0, defaultValue='null'}, isSolved=Column{name='isSolved', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=0, defaultValue='null'}}, foreignKeys=[], indices=[]}
Found:
TableInfo{name='Crime', columns={date=Column{name='date', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=0, defaultValue='null'}, requirePolice=Column{name='requirePolice', type='TEXT', affinity='2', notNull=true, primaryKeyPosition=0, defaultValue=''}, isSolved=Column{name='isSolved', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=0, defaultValue='null'}, id=Column{name='id', type='TEXT', affinity='2', notNull=true, primaryKeyPosition=1, defaultValue='null'}, suspect=Column{name='suspect', type='TEXT', affinity='2', notNull=true, primaryKeyPosition=0, defaultValue='null'}, title=Column{name='title', type='TEXT', affinity='2', notNull=true, primaryKeyPosition=0, defaultValue='null'}}, foreignKeys=[], indices=[]}
    at androidx.room.RoomOpenHelper.onUpgrade(RoomOpenHelper.java:103)
    at androidx.sqlite.db.framework.FrameworkSQLiteOpenHelper$OpenHelper.onUpgrade(FrameworkSQLiteOpenHelper.java:177)
    at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:416)
    at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:316)
    at androidx.sqlite.db.framework.FrameworkSQLiteOpenHelper$OpenHelper.getWritableSupportDatabase(FrameworkSQLiteOpenHelper.java:145)
    at androidx.sqlite.db.framework.FrameworkSQLiteOpenHelper.getWritableDatabase(FrameworkSQLiteOpenHelper.java:106)
    at androidx.room.RoomDatabase.inTransaction(RoomDatabase.java:731)
    at androidx.room.RoomDatabase.assertNotSuspendingTransaction(RoomDatabase.java:508)
    at androidx.room.RoomDatabase.query(RoomDatabase.java:551)
    at androidx.room.util.DBUtil.query(DBUtil.java:83)
    at com.bignerdranch.android.criminalintent.database.CrimeDao_Impl$3.call(CrimeDao_Impl.java:158)
    at com.bignerdranch.android.criminalintent.database.CrimeDao_Impl$3.call(CrimeDao_Impl.java:155)
    at androidx.room.RoomTrackingLiveData$1.run(RoomTrackingLiveData.java:90)
    ... 3 more

错误原因分析 #

看日志里的Expected和Found对比就能发现核心问题：

• 你的Crime数据类中requirePolice是Boolean类型，Room会自动将Boolean映射为SQLite的INTEGER类型（用0代表false，1代表true）
• 但你写的迁移SQL把这个字段创建成了TEXT类型，还设置了默认值为空字符串''，这和Room预期的表结构完全不匹配，所以触发了Migration验证失败的异常。

解决方案 #

1. 修正迁移SQL语句 #

把migration_2_3中的SQL改成匹配Room预期的类型和默认值：

val migration_2_3 = object : Migration(2,3){
    override fun migrate(database: SupportSQLiteDatabase) {
        // Boolean对应SQLite的INTEGER，默认值0对应false
        database.execSQL("ALTER TABLE Crime ADD COLUMN requirePolice INTEGER NOT NULL DEFAULT 0")
    }
}

2. 清理测试设备上的旧数据库 #

如果你已经在测试设备上运行过错误的迁移版本，数据库中已经创建了错误类型的字段，那么需要卸载当前应用后重新运行——因为SQLite不支持修改已存在字段的类型，开发阶段这是最快捷的清理方式。

3. 优化数据库构建器配置 #

可以把多个迁移合并到一个addMigrations调用中，代码更简洁：

private val database: CrimeDatabase = Room.databaseBuilder(
    context.applicationContext,
    CrimeDatabase::class.java,
    DATABASE_NAME
)
.addMigrations(migration_1_2, migration_2_3)
.build()

完成以上修改后，Room就能正确匹配数据类和数据库表的结构，迁移崩溃问题就会解决。

内容的提问来源于stack exchange，提问作者Saher Al-Sous