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Tutorial: Callbacks

This tutorial assumes you have successfully completed the First Steps: Command-line tutorial. If you have not done so, please do so first. This tutorial picks up where that one left off.

This brief tutorial will teach how to use callbacks. It will take you through the steps on how to create and use them.

Introduction

Callbacks let you hook into Flyway’s lifecycle. This is particularly useful when you execute the same housekeeping action over and over again.

They are typically used for

• Recompiling procedures
• Updating materialized views
• Storage housekeeping (VACUUM for PostgreSQL for example)

Reviewing the status

After having completed the First Steps: Command-line, you can now execute

flyway-9.8.1> flyway info

This should give you the following status:

Database: jdbc:h2:file:./foobardb (H2 1.4)
                     
+-----------+---------+---------------------+------+---------------------+---------+----------+
| Category  | Version | Description         | Type | Installed On        | State   | Undoable |
+-----------+---------+---------------------+------+---------------------+---------+----------+
| Versioned | 1       | Create person table | SQL  | 2017-12-21 18:05:10 | Success | No       |
| Versioned | 2       | Add people          | SQL  | 2017-12-21 18:05:10 | Success | No       |
+-----------+---------+---------------------+------+---------------------+---------+----------+

Creating a callback

Now let’s create a callback to flush all data to disk before a migration run. To do so, we’ll make use of Flyway’s beforeMigrate callback.

So go ahead and create beforeMigrate.sql in the /sql directory:

CHECKPOINT SYNC;

Triggering the callback

To trigger the execution of the callback, we’ll clean and migrate the database again.

So go ahead and invoke

flyway-9.8.1> flyway clean migrate

This will give you the following result:

Database: jdbc:h2:file:./foobardb (H2 1.4)
Successfully cleaned schema "PUBLIC" (execution time 00:00.003s)
Successfully validated 2 migrations (execution time 00:00.010s)
Executing SQL callback: beforeMigrate
Creating Schema History table: "PUBLIC"."flyway_schema_history"
Current version of schema "PUBLIC": << Empty Schema >>
Migrating schema "PUBLIC" to version 1 - Create person table
Migrating schema "PUBLIC" to version 2 - Add people
Successfully applied 2 migrations to schema "PUBLIC" (execution time 00:00.034s)

As expected we can see that the beforeMigrate callback was triggered and executed successfully before the migrate operation. Each time you invoke migrate again in the future, the callback will now be executed again.

Summary

In this brief tutorial we saw how to

• create callbacks
• triggers the execution of callbacks

Read the callback documentation