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Code - Flyway Plugin Development.md

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Flyway Plugin Development - Code

Code: Flyway Plugin Development

Between Flyway 9.0.0 and Flyway 10.0.0, the architecture of Flyway has changed significantly to a modularized system. This has made it easier to develop plugins for Flyway to expand its capabilities and allow for a more streamlined approach for contributions. This tutorial will walk you through the steps of creating a plugin for Flyway 10.0.0.

Creating a Flyway plugin

To create a Flyway plugin, you will need to create a new Maven module depending on the flyway-core module and any other modules related to your database type. For example, if you are creating a database support plugin for a PostgreSQL variation, you will need to depend on the flyway-core and flyway-database-postgresql modules.

Plugins are loaded in Flyway via the Flyway Plugin Register which uses the Java ServiceLoader to load plugins at runtime. To do this you will need a class which implements org.flywaydb.core.extensibility.Plugin or a child interface and to create a file in src/main/resources/META-INF/services called org.flywaydb.core.extensibility.Plugin which contains the fully qualified name of your plugin class.

Example org.flywaydb.core.extensibility.Plugin:

org.flywaydb.database.cockroachdb.CockroachDBDatabaseType
org.flywaydb.database.postgresql.PostgreSQLDatabaseType
org.flywaydb.database.postgresql.PostgreSQLConfigurationExtension

Plugin types

Flyway is now expandable via the Plugin interface within flyway-core. This interface allows flyway to load plugins at runtime to use them to extend its functionality and can be extended to provide helper interfaces for specific functionality. For the purposes of this tutorial, we will be explaining the following plugin types:

  • PluginMetadata
  • DatabaseType
  • ConfigurationExtension

PluginMetadata

The PluginMetadata interface (org.flywaydb.core.extensibility.PluginMetadata) is used to provide Flyway with metadata about a plugin.

DatabaseType

Open source database plugins have been moved to a separate repository, see: Contributing Database Compatibility to Flyway

ConfigurationExtension

The ConfigurationExtension interface (org.flywaydb.core.extensibility.ConfigurationExtension) is used to provide Flyway with the ability to support new configuration options. This is usually used to provide new configuration options for plugins. ConfigurationExtensions require the following methods to be implemented:

  • String getNamespace() - This is the namespace for the configuration option under the flyway configuration domain. This is used to group configuration options together. For example the configuration flyway.postgresql.transactional.lock has the namespace postgresql
  • String getConfigurationParameterFromEnvironmentVariable(String environmentVariable) - This is used to get the configuration parameter from an environment variable. This is used to allow users to set configuration options via environment variables. For example, the configuration flyway.postgresql.transactional.lock can be set via the environment variable FLYWAY_POSTGRESQL_TRANSACTIONAL_LOCK. This is only necessary for legacy Flyway configuration. If you are using new Flyway configuration, the Environment Variable format will by default be screaming snake case of your configuration option's path.

Flyway Plugin Archetype

To make it easier to create plugins for Flyway, we have created a Maven archetype to create a basic plugin project. This archetype can be found in the flyway-plugin-archetype module in the flyway repository.

Installing locally

If you wish to compile the Flyway Plugin Archetype locally, you can do so by running the following command from the root of the flyway repository:

mvn clean install -DskipTests -DskipIts -pl flyway-plugin-archetype -am

Using the archetype

To create a new Flyway plugin project via commandline, run the following command:

mvn archetype:generate -DarchetypeGroupId=org.flywaydb 
                       -DarchetypeArtifactId=flyway-plugin-archetype
                       -DarchetypeVersion=10.0.0
                       -DgroupId=org.flywaydb 
                       -DartifactId=my-flyway-plugin
                       -Dversion=10.0.1-SNAPSHOT
                       -Dpackage=org.flywaydb.community.database.myflywayplugin

If using IntelliJ, you can create a new project by selecting File > New > Project... and selecting Maven Archetype from the list of project types. Then fill in with the appropriate information, see below, and click create:

image

This will create a new project in the my-flyway-plugin directory. This directory will contain the following:

  • a pom.xml file which you can use to build your plugin
  • a src/main/java directory containing the source code for your plugin
  • a src/test/java directory containing unit tests for your plugin
  • a basic Plugin class which you can extend to implement your plugin in the package specified in your generate command
  • a META-INF/services directory containing a file which you can use to register your plugin with Flyway.