All the common extension types for HUBzero can include their own migrations directory. Migrations are used for installing the extension into the required tables for the CMS to know about said extension's existence, installing any needed tables, installing sample data, etc.

To illustrate the typical component directory structures and files:

/app
.. /modules
.. .. /mod_example
.. .. .. /migrations
.. .. .. .. /Migration20190301102219ModExample.php
.. .. .. /tmpl
.. .. .. .. default.php
.. .. .. helper.php
.. .. .. mod_example.php
.. .. .. mod_example.xml

See the Migrations documentation for more about naming conventions, setup, etc.

Modules typically have at least one initial migration for registering the extension with the CMS. This migration typically just involves calling the addModuleEntry helper method:

<?php

use Hubzero\Content\Migration\Base;

// No direct access
defined('_HZEXEC_') or die();

/**
 * Migration script for registering the example plugin
 **/
class Migration20190301102219ModExample extends Base
{
    /**
     * Up
     **/
    public function up()
    {
        // Register the module
        //
        // @param   string  $element  (required) Module element
        // @param   int     $enabled  (optional, default: 1) Whether or not the module should be enabled
	// @param   string  $params          (optional) Plugin params (if already known)
	// @param   int     $client   (optional, default: 0) Client [site=0, admin=1]
        $this->addModuleEntry('mod_example');
    }

    /**
     * Down
     **/
    public function down()
    {
        $this->deleteModuleEntry('mod_example');
    }
}

That's all there is to it! The addModuleEntry method adds the necessary entries to the needed database tables for the CMS to be aware of the module's existence.

For a module to appear anywhere, a new instance of that module must be created and assigned to a position. This above migration just makes the CMS aware of the module's presence so that a new instance can be created.