Migration.kt
/*
* Copyright 2021 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.room.migration
import androidx.sqlite.db.SupportSQLiteDatabase
/**
* Creates [Migration] from [startVersion] to [endVersion] that runs [migrate] to perform
* the necessary migrations.
*
* A migration can handle more than 1 version (e.g. if you have a faster path to choose when
* going version 3 to 5 without going to version 4). If Room opens a database at version
* 3 and latest version is < 5, Room will use the migration object that can migrate from
* 3 to 5 instead of 3 to 4 and 4 to 5.
*
* If there are not enough migrations provided to move from the current version to the latest
* version, Room will clear the database and recreate so even if you have no changes between 2
* versions, you should still provide a Migration object to the builder.
*
* [migrate] cannot access any generated Dao in this method.
*
* [migrate] is already called inside a transaction and that transaction
* might actually be a composite transaction of all necessary `Migration`s.
*/
public fun Migration(
startVersion: Int,
endVersion: Int,
migrate: (SupportSQLiteDatabase) -> Unit
): Migration = MigrationImpl(startVersion, endVersion, migrate)
private class MigrationImpl(
startVersion: Int,
endVersion: Int,
val migrateCallback: (SupportSQLiteDatabase) -> Unit
) : Migration(startVersion, endVersion) {
override fun migrate(database: SupportSQLiteDatabase) = migrateCallback(database)
}