Android Room 从 SQLiteOpenHelper 迁移答案

【问题标题】：Android Room migrate from SQLiteOpenHelperAndroid Room 从 SQLiteOpenHelper 迁移
【发布时间】：2021-06-29 17:11:43
【问题描述】：

我正在将数据库访问从 SQLiteOpenHelper 迁移到 Room。
但是我注意到 Room 不接受数据库架构。
有一个表的主键由两列组成，其中一列可以为空。在 Room 中，主键不能为空。

所以我想在开始使用 Room 之前执行查询以修复架构。

使用 SQLiteOpenHelper 设置的当前数据库版本为 8，我将 Room 的数据库版本设置为 9。

我在 Room 中添加了迁移，因此可以执行升级但没有任何反应。

Room.databaseBuilder(
    context.applicationContext,
    AppDatabase::class.java,
    "databse")
    .addMigrations(MIGRATION_8_9)
    .fallbackToDestructiveMigration()
    .build()



private val MIGRATION_8_9 = object: Migration(8, 9) {
    override fun migrate(database: SupportSQLiteDatabase) {
        L.tag(TAG).info("Performing database migration from SQLiteHelper to Room")
        database.execSQL("DO SOME WORK")
    }

}

如何在开始使用 Room 之前运行 SQLite 语句来修复数据库架构？

【问题讨论】：

标签： android android-sqlite android-room

【解决方案1】：

我在 Room 中添加了迁移，因此可以执行升级但没有任何反应。

您的代码应该可以工作（根据下面的演示）但是只有当您实际尝试对数据库执行某些操作而不是实例化它时。即数据库在实际需要时才打开。

考虑以下示例：-

@Database(entities = [MyTable::class],version = 9,exportSchema = false)
abstract class TheDatabase: RoomDatabase() {
    abstract fun getAllDao(): AllDao

    companion object {
        private var instance: TheDatabase? = null
        private val TAG = "ROOMDBINFO"

        fun getInstance(context: Context): TheDatabase {
            if (instance == null) {
                instance = Room.databaseBuilder(context,TheDatabase::class.java,"database")
                    .allowMainThreadQueries()
                    .addMigrations(MIGRATION_8_9)
                    .build()

            }
            return instance as TheDatabase
        }
        private val MIGRATION_8_9 = object: Migration(8, 9) {
            override fun migrate(database: SupportSQLiteDatabase) {
                Log.d(TAG,"Performing database migration from SQLiteHelper to Room")
                var csr = database.query("SELECT * FROM sqlite_master")
                DatabaseUtils.dumpCursor(csr)
            }
        }
    }
}

还有：-

class MainActivity : AppCompatActivity() {

    lateinit var db: TheDatabase
    lateinit var dao: AllDao
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        
        createBaseDatabaseToMigrate() //<<<<< Create and populate the database before Room
        
        db = TheDatabase.getInstance(this)
        dao = db.getAllDao()
        //dao.getAllFromMytable() //<<<<< Commented out so DB isn't opened

    }


    /* This will create the database if it doesn't exist*/
    private fun createBaseDatabaseToMigrate() {
        val TAG = "ORIGINALDATA"
        var db = openOrCreateDatabase(this.getDatabasePath("database").absolutePath,0,null)
        db.beginTransaction()
        db.execSQL("CREATE TABLE IF NOT EXISTS mytable (col1 INTEGER NOT NULL, col2 INTEGER, col3 TEXT, PRIMARY KEY(col1,col2))")
        var csr = db.query("mytable",null,null,null,null,null,null)
        var dataExists = csr.count > 0
        csr.close()
        if (!dataExists) {
            db.execSQL("INSERT OR IGNORE INTO mytable VALUES(1,null,'data1'),(2,2,'data2'),(3,3,'data3');")
            db.execSQL("PRAGMA user_version = 8;")
        } else {
            Log.d(TAG,"Data already existed.")
        }
        csr = db.query("mytable",null,null,null,null,null,null)
        while(csr.moveToNext()) {
            Log.d(TAG,
                "COL1 = ${csr.getLong(csr.getColumnIndex("col1"))} " +
                        "COL2 = ${csr.getLong(csr.getColumnIndex("col2"))} " +
                        "COL3 = ${csr.getString(csr.getColumnIndex("col3"))}"
            )
        }
        csr = db.query("sqlite_master",null,null,null,null,null,null)
        DatabaseUtils.dumpCursor(csr)
        csr.close()
        db.setTransactionSuccessful()
        db.endTransaction()
        db.close()
    }
}

注意 createDatabaseToMigrate 展示了在我开始使用 Room 之前如何运行 SQLite 语句来修复数据库架构 。但是，我们不建议/不需要这样做。
为了方便和简洁，在主线程上运行。
注意 dao.getAllFromMytable() 已被注释掉。

测试/演示

使用上面的代码运行它，根据日志，迁移中没有任何反应：-

2021-06-30 06:47:18.341 W/onversion8_to_: Accessing hidden method Landroid/view/ViewGroup;->makeOptionalFitsSystemWindows()V (light greylist, reflection)
2021-06-30 06:47:18.407 D/ORIGINALDATA: Data already existed.
2021-06-30 06:47:18.408 D/ORIGINALDATA: COL1 = 1 COL2 = 0 COL3 = 0
2021-06-30 06:47:18.408 D/ORIGINALDATA: COL1 = 2 COL2 = 2 COL3 = 0
2021-06-30 06:47:18.408 D/ORIGINALDATA: COL1 = 3 COL2 = 3 COL3 = 0
2021-06-30 06:47:18.408 I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@be55dc1
2021-06-30 06:47:18.408 I/System.out: 0 {
2021-06-30 06:47:18.409 I/System.out:    type=table
2021-06-30 06:47:18.409 I/System.out:    name=android_metadata
2021-06-30 06:47:18.409 I/System.out:    tbl_name=android_metadata
2021-06-30 06:47:18.409 I/System.out:    rootpage=3
2021-06-30 06:47:18.409 I/System.out:    sql=CREATE TABLE android_metadata (locale TEXT)
2021-06-30 06:47:18.409 I/System.out: }
2021-06-30 06:47:18.409 I/System.out: 1 {
2021-06-30 06:47:18.409 I/System.out:    type=table
2021-06-30 06:47:18.409 I/System.out:    name=mytable
2021-06-30 06:47:18.409 I/System.out:    tbl_name=mytable
2021-06-30 06:47:18.409 I/System.out:    rootpage=4
2021-06-30 06:47:18.409 I/System.out:    sql=CREATE TABLE mytable (col1 INTEGER NOT NULL, col2 INTEGER, col3 TEXT, PRIMARY KEY(col1,col2))
2021-06-30 06:47:18.409 I/System.out: }
2021-06-30 06:47:18.409 I/System.out: 2 {
2021-06-30 06:47:18.409 I/System.out:    type=index
2021-06-30 06:47:18.410 I/System.out:    name=sqlite_autoindex_mytable_1
2021-06-30 06:47:18.410 I/System.out:    tbl_name=mytable
2021-06-30 06:47:18.410 I/System.out:    rootpage=5
2021-06-30 06:47:18.410 I/System.out:    sql=null
2021-06-30 06:47:18.410 I/System.out: }
2021-06-30 06:47:18.410 I/System.out: <<<<<
2021-06-30 06:47:18.439 D/OpenGLRenderer: Skia GL Pipeline
2021-06-30 06:47:18.460 W/onversion8_to_: Accessing hidden method Landroid/graphics/Insets;->of(IIII)Landroid/graphics/Insets; (light greylist, linking)

作为第二次运行，//dao.getAllFromMytable() //<<<<< Commented out so DB isn't 更改为 dao.getAllFromMytable() //<<<<< Commented out so DB isn't opened

和：-

2021-06-30 06:51:28.059 W/onversion8_to_: Accessing hidden method Landroid/view/ViewGroup;->makeOptionalFitsSystemWindows()V (light greylist, reflection)
2021-06-30 06:51:28.129 D/ORIGINALDATA: Data already existed.
2021-06-30 06:51:28.129 D/ORIGINALDATA: COL1 = 1 COL2 = 0 COL3 = 0
2021-06-30 06:51:28.129 D/ORIGINALDATA: COL1 = 2 COL2 = 2 COL3 = 0
2021-06-30 06:51:28.130 D/ORIGINALDATA: COL1 = 3 COL2 = 3 COL3 = 0
2021-06-30 06:51:28.130 I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@be55dc1
2021-06-30 06:51:28.130 I/System.out: 0 {
2021-06-30 06:51:28.130 I/System.out:    type=table
2021-06-30 06:51:28.131 I/System.out:    name=android_metadata
2021-06-30 06:51:28.131 I/System.out:    tbl_name=android_metadata
2021-06-30 06:51:28.131 I/System.out:    rootpage=3
2021-06-30 06:51:28.131 I/System.out:    sql=CREATE TABLE android_metadata (locale TEXT)
2021-06-30 06:51:28.131 I/System.out: }
2021-06-30 06:51:28.131 I/System.out: 1 {
2021-06-30 06:51:28.131 I/System.out:    type=table
2021-06-30 06:51:28.131 I/System.out:    name=mytable
2021-06-30 06:51:28.131 I/System.out:    tbl_name=mytable
2021-06-30 06:51:28.131 I/System.out:    rootpage=4
2021-06-30 06:51:28.131 I/System.out:    sql=CREATE TABLE mytable (col1 INTEGER NOT NULL, col2 INTEGER, col3 TEXT, PRIMARY KEY(col1,col2))
2021-06-30 06:51:28.131 I/System.out: }
2021-06-30 06:51:28.131 I/System.out: 2 {
2021-06-30 06:51:28.131 I/System.out:    type=index
2021-06-30 06:51:28.132 I/System.out:    name=sqlite_autoindex_mytable_1
2021-06-30 06:51:28.132 I/System.out:    tbl_name=mytable
2021-06-30 06:51:28.132 I/System.out:    rootpage=5
2021-06-30 06:51:28.132 I/System.out:    sql=null
2021-06-30 06:51:28.132 I/System.out: }
2021-06-30 06:51:28.133 I/System.out: <<<<<




2021-06-30 06:51:28.161 D/ROOMDBINFO: Performing database migration from SQLiteHelper to Room
2021-06-30 06:51:28.162 I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@71135f2
2021-06-30 06:51:28.162 I/System.out: 0 {
2021-06-30 06:51:28.162 I/System.out:    type=table
2021-06-30 06:51:28.162 I/System.out:    name=android_metadata
2021-06-30 06:51:28.162 I/System.out:    tbl_name=android_metadata
2021-06-30 06:51:28.162 I/System.out:    rootpage=3
2021-06-30 06:51:28.162 I/System.out:    sql=CREATE TABLE android_metadata (locale TEXT)
2021-06-30 06:51:28.162 I/System.out: }
2021-06-30 06:51:28.162 I/System.out: 1 {
2021-06-30 06:51:28.163 I/System.out:    type=table
2021-06-30 06:51:28.163 I/System.out:    name=mytable
2021-06-30 06:51:28.163 I/System.out:    tbl_name=mytable
2021-06-30 06:51:28.163 I/System.out:    rootpage=4
2021-06-30 06:51:28.163 I/System.out:    sql=CREATE TABLE mytable (col1 INTEGER NOT NULL, col2 INTEGER, col3 TEXT, PRIMARY KEY(col1,col2))
2021-06-30 06:51:28.163 I/System.out: }
2021-06-30 06:51:28.163 I/System.out: 2 {
2021-06-30 06:51:28.163 I/System.out:    type=index
2021-06-30 06:51:28.163 I/System.out:    name=sqlite_autoindex_mytable_1
2021-06-30 06:51:28.163 I/System.out:    tbl_name=mytable
2021-06-30 06:51:28.163 I/System.out:    rootpage=5
2021-06-30 06:51:28.164 I/System.out:    sql=null
2021-06-30 06:51:28.164 I/System.out: }
2021-06-30 06:51:28.164 I/System.out: <<<<<




2021-06-30 06:51:28.169 D/AndroidRuntime: Shutting down VM
2021-06-30 06:51:28.171 E/AndroidRuntime: FATAL EXCEPTION: main
    Process: a.a.so68183015kotlinroommigrationconversion8_to_9, PID: 24101
    java.lang.RuntimeException: Unable to start activity ComponentInfo{a.a.so68183015kotlinroommigrationconversion8_to_9/a.a.so68183015kotlinroommigrationconversion8_to_9.MainActivity}: java.lang.IllegalStateException: Migration didn't properly handle: mytable(a.a.so68183015kotlinroommigrationconversion8_to_9.MyTable).
     Expected:
    TableInfo{name='mytable', columns={col2=Column{name='col2', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=2, defaultValue='null'}, col3=Column{name='col3', type='TEXT', affinity='2', notNull=true, primaryKeyPosition=0, defaultValue='null'}, col1=Column{name='col1', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=1, defaultValue='null'}}, foreignKeys=[], indices=[]}
     Found:
    TableInfo{name='mytable', columns={col2=Column{name='col2', type='INTEGER', affinity='3', notNull=false, primaryKeyPosition=2, defaultValue='null'}, col3=Column{name='col3', type='TEXT', affinity='2', notNull=false, primaryKeyPosition=0, defaultValue='null'}, col1=Column{name='col1', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=1, defaultValue='null'}}, foreignKeys=[], indices=[]}
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
     Caused by: java.lang.IllegalStateException: Migration didn't properly handle: mytable(a.a.so68183015kotlinroommigrationconversion8_to_9.MyTable).
     Expected:
    TableInfo{name='mytable', columns={col2=Column{name='col2', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=2, defaultValue='null'}, col3=Column{name='col3', type='TEXT', affinity='2', notNull=true, primaryKeyPosition=0, defaultValue='null'}, col1=Column{name='col1', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=1, defaultValue='null'}}, foreignKeys=[], indices=[]}
     Found:
    TableInfo{name='mytable', columns={col2=Column{name='col2', type='INTEGER', affinity='3', notNull=false, primaryKeyPosition=2, defaultValue='null'}, col3=Column{name='col3', type='TEXT', affinity='2', notNull=false, primaryKeyPosition=0, defaultValue='null'}, col1=Column{name='col1', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=1, defaultValue='null'}}, foreignKeys=[], indices=[]}
        at androidx.room.RoomOpenHelper.onUpgrade(RoomOpenHelper.java:103)
        at androidx.sqlite.db.framework.FrameworkSQLiteOpenHelper$OpenHelper.onUpgrade(FrameworkSQLiteOpenHelper.java:183)
        at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:398)
        at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:298)
        at androidx.sqlite.db.framework.FrameworkSQLiteOpenHelper$OpenHelper.getWritableSupportDatabase(FrameworkSQLiteOpenHelper.java:151)
        at androidx.sqlite.db.framework.FrameworkSQLiteOpenHelper.getWritableDatabase(FrameworkSQLiteOpenHelper.java:112)
        at androidx.room.RoomDatabase.inTransaction(RoomDatabase.java:705)
        at androidx.room.RoomDatabase.assertNotSuspendingTransaction(RoomDatabase.java:482)
        at a.a.so68183015kotlinroommigrationconversion8_to_9.AllDao_Impl.getAllFromMytable(AllDao_Impl.java:28)
2021-06-30 06:51:28.172 E/AndroidRuntime:     at a.a.so68183015kotlinroommigrationconversion8_to_9.MainActivity.onCreate(MainActivity.kt:20)
        at android.app.Activity.performCreate(Activity.java:7136)
        at android.app.Activity.performCreate(Activity.java:7127)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
            ... 11 more
2021-06-30 06:51:28.185 I/Process: Sending signal. PID: 24101 SIG: 9

您可以看到迁移已被调用。

实际迁移

基于上述但修改TheDatabase类并添加转换，然后：-

这种情况下的@Entity 是：-

@Entity(tableName = "mytable", primaryKeys = ["col1","col2"])
data class MyTable(
    val col1: Long,
    val col2: Long,
    val col3: String
)

即在这种情况下， col2 和 col3 列都没有 NOT NULL 但 room 期望它们应该。（查看 cmets re SQL，因为它是从生成的 java 复制而来的）。

那么（可能有点啰嗦）TheDatabase 可能是：-

@Database(entities = [MyTable::class],version = 9,exportSchema = false)
abstract class TheDatabase: RoomDatabase() {
    abstract fun getAllDao(): AllDao

    companion object {
        private var instance: TheDatabase? = null
        private val TAG = "ROOMDBINFO"

        fun getInstance(context: Context): TheDatabase {
            if (instance == null) {
                instance = Room.databaseBuilder(context,TheDatabase::class.java,"database")
                    .allowMainThreadQueries()
                    .addMigrations(MIGRATION_8_9)
                    .build()

            }
            return instance as TheDatabase
        }

        // copied from java(generated) <thisclass>_Impl.java>  (i.e. TheDatabase_Impl):-
        // From the createAllTables method
        // _db.execSQL("CREATE TABLE IF NOT EXISTS `mytable` (`col1` INTEGER NOT NULL, `col2` INTEGER NOT NULL, `col3` TEXT NOT NULL, PRIMARY KEY(`col1`, `col2`))");
        private val MIGRATION_8_9 = object: Migration(8, 9) {
            override fun migrate(database: SupportSQLiteDatabase) {
                val inTransaction = database.inTransaction()
                Log.d(TAG,"Performing database migration from SQLiteHelper to Room")
                if (!inTransaction) database.beginTransaction()
                var csr = database.query("SELECT * FROM sqlite_master")
                DatabaseUtils.dumpCursor(csr)
                csr.close()
                // SEE ABOVE FROM GETTING CORRECT SQL
                database.execSQL("CREATE TABLE IF NOT EXISTS `mytable_new` (`col1` INTEGER NOT NULL, `col2` INTEGER NOT NULL, `col3` TEXT NOT NULL, PRIMARY KEY(`col1`, `col2`))")
                csr = database.query("SELECT coalesce(col1,0) AS col1, coalesce(col2,0) AS col2, coalesce(col3,'nothing') AS col3 FROM `mytable`")
                DatabaseUtils.dumpCursor(csr)
                var cv = ContentValues()
                while (csr.moveToNext()) {
                    cv.clear()
                    cv.put("col1",csr.getLong(csr.getColumnIndex("col1")))
                    cv.put("col2",csr.getLong(csr.getColumnIndex("col2")))
                    cv.put("col3",csr.getString(csr.getColumnIndex("col3")))
                    database.insert("`mytable_new`",OnConflictStrategy.IGNORE,cv)
                }
                csr.close()
                csr = database.query("SELECT * FROM sqlite_master")
                DatabaseUtils.dumpCursor(csr)
                csr = database.query("SELECT * FROM `mytable`")
                while (csr.moveToNext()) {
                    Log.d(TAG,
                        "COL1 = ${csr.getLong(csr.getColumnIndex("col1"))} " +
                                "COL2 = ${csr.getLong(csr.getColumnIndex("col2"))} " +
                                "COL3 = ${csr.getString(csr.getColumnIndex("col3"))}"
                    )
                }
                csr.close()
                database.execSQL("ALTER TABLE `mytable` RENAME TO `mytable_original`")
                database.execSQL("ALTER TABLE `mytable_new` RENAME TO `mytable`")
                database.execSQL("DROP TABLE IF EXISTS `mytable_original`")
                csr = database.query("SELECT * FROM sqlite_master")
                DatabaseUtils.dumpCursor(csr)
                csr.close()
                if (!inTransaction) {
                    database.setTransactionSuccessful()
                    database.endTransaction()
                }
            }
        }
    }
}

运行时（应用程序被卸载，因此创建了原始的非 Room DB）``mytable 被转换（col2 中的 null 由于使用了合并而被转换为 0（显然你可能想要另一个值而不是 0））。随后的运行就可以了。

（回答太长，无法包含日志，因此您必须相信我）

【讨论】：

你是对的。有用。我的问题是我试图运行一个脚本而不是单独运行每个语句。没有错误。谢谢。