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/*
* Copyright (C) 2017 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 android.arch.persistence.room.migration;
import android.arch.persistence.db.SupportSQLiteDatabase;
import android.support.annotation.NonNull;
/**
* Base class for a database migration.
* <p>
* Each migration can move between 2 versions that are defined by {@link #startVersion} and
* {@link #endVersion}.
* <p>
* 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.
* <p>
* 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.
*/
public abstract class Migration {
public final int startVersion;
public final int endVersion;
/**
* Creates a new migration between {@code startVersion} and {@code endVersion}.
*
* @param startVersion The start version of the database.
* @param endVersion The end version of the database after this migration is applied.
*/
public Migration(int startVersion, int endVersion) {
this.startVersion = startVersion;
this.endVersion = endVersion;
}
/**
* Should run the necessary migrations.
* <p>
* This class cannot access any generated Dao in this method.
* <p>
* This method is already called inside a transaction and that transaction might actually be a
* composite transaction of all necessary {@code Migration}s.
*
* @param database The database instance
*/
public abstract void migrate(@NonNull SupportSQLiteDatabase database);
}
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