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/*
 * Copyright 2010-2020 Redgate Software Ltd
 *
 * 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 cn.com.pism.frc.resourcescanner;


/**
 * Interface to be implemented by Java-based Migrations.
 *
 * Java-based migrations are a great fit for all changes that can not easily be expressed using SQL.
 *
 * These would typically be things like
 * 
 *     BLOB & CLOB changes
 *     Advanced bulk data changes (Recalculations, advanced format changes, ...)
 * 
 *
 * Migration classes implementing this interface will be
 * automatically discovered when placed in a location on the classpath.
 *
 * Most users will be better served by subclassing subclass {@link BaseJavaMigration} instead of implementing this
 * interface directly, as {@link BaseJavaMigration} encourages the use of Flyway's default naming convention and
 * comes with sensible default implementations of all methods (except migrate of course) while at the same time also
 * providing better isolation against future additions to this interface.
 */
public interface JavaMigration {
    /**
     * @return The version of the schema after the migration is complete. {@code null} for repeatable migrations.
     */
    MigrationVersion getVersion();

    /**
     * @return The description of this migration for the migration history. Never {@code null}.
     */
    String getDescription();

    /**
     * Computes the checksum of the migration.
     *
     * @return The checksum of the migration.
     */
    Integer getChecksum();

    /**
     * Whether this is an undo migration for a previously applied versioned migration.
     *
     * @return {@code true} if it is, {@code false} if not. Always {@code false} for repeatable migrations.
     */
    boolean isUndo();

    /**
     * Whether the execution should take place inside a transaction. Almost all implementation should return {@code true}.
     * This however makes it possible to execute certain migrations outside a transaction. This is useful for databases
     * like PostgreSQL and SQL Server where certain statement can only execute outside a transaction.
     *
     * @return {@code true} if a transaction should be used (highly recommended), or {@code false} if not.
     */
    boolean canExecuteInTransaction();

    /**
     * Executes this migration. The execution will automatically take place within a transaction, when the underlying
     * database supports it and the canExecuteInTransaction returns {@code true}.
     *
     * @param context The context relevant for this migration, containing things like the JDBC connection to use and the
     *                current Flyway configuration.
     * @throws Exception when the migration failed.
     */
    void migrate(Context context) throws Exception;
}