What is required to get a custom module to appear in uninstall list?

Question

Solution: Ayesh K provides the correct answer below.

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What is required to get a custom module to appear in uninstall list? I thought all you had to do was specify a database schema in hook_schema(), but I've done so and my module does not appear in the uninstall list. Currently my module consists of the following code in the .install file:

<?php

/**
 * Table schema definition for the Events Sponsors module.
 */
function event_sponsors_schema() {
    $schema['event_sponsors_sponsors'] = array(
        'description' => 'A collection of event sponsors.',
        'fields' => array(
            'id' => array(
                'type' => 'serial',
                'not null' => TRUE,
                'unsigned' => TRUE,
                'description' => "Unique ID for the sponsor.",
            ),
            'name' => array(
                'type' => 'varchar',
                'length' => '255',
                'not null' => TRUE,
                'description' => 'The name of the sponsor.',
            ),
        ),
        'primary key' => array('id'),
        'unique keys' => array(
            'id' => array('id'),
        ),
    );

    $schema['event_sponsors_sponsor_relations'] = array(
        'description' => 'Maintains sponsor and node relations.',
        'fields' => array(
            'sid' => array(
                'type' => 'int',
                'not null' => TRUE,
                'unsigned' => TRUE,
                'description' => 'The sponsor ID, as can be found in the sponsors table.',
            ),
            'nid' => array(
                'type' => 'int',
                'not null' => TRUE,
                'unsigned' => TRUE,
                'description' => 'The node ID as can be found in the node table.',
            ),
            'ordinal' => array(
                'type' => 'int',
                'not null' => TRUE,
                'unsigned' => TRUE,
                'description' => 'The order this sponsor appears alongside the node.',
            ),
        ),
        'primary keys' => array('sid','nid'),
        'unique keys' => array(
            'sid' => array('sid'),
            'nid' => array('nid'),
        ),
    );

    return $schema;
}

Any insight is appreciated.

Answer 1

For Drupal 6, you needed to install/uninstall schema using hook_install and hook_uninstall.

This is not necessary for Drupal 7.

Module will appear in uninstall list if both of these conditions are met:

• module implements hook_schema OR hook_uninstall in its .install file.
• module was enabled once and now is in disabled status.

If the only purpose of hook_uninstall is to uninstall the schema, you do not need a hook_uninstall function. For variable_del(), etc: you need. If you have any of these and module has data in the site already, you will see the uninstall check box.

Answer 2

Use hook_uninstall() like this way.
variables must not undefined.

function mymodule_uninstall() {
  variable_del('mymodule_var');
  variable_del('mymodule_var2');
}

Answer 3

A very simple solution for newbies like me in drupal 7.

You can't uninstall a module when it's running or active. So try, to disable your module first and it should appear to uninstall list afterwards.