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WordPress: Creating Custom Widgets and Plugins with PHP
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Creating an uninstall function


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WordPress: Creating Custom Widgets and Plugins with PHP

with Drew Falkman

Video: Creating an uninstall function

One of the potential problems with open development environments like WordPress is that after a period of time of using plugins that have options from in the database and new database tables, and all this sort of thing, and then deciding not to use them, it's pretty easy to get some database bloat, and have a lot of things hanging out there. So it's a best practice, as plugin developers, to create some sort of uninstall script that removes these items that are plugin uses when they're removed. As of WordPress 2.7, we have a couple of ways to do this. One way is that we can register an uninstall hook, which will essentially set up a function that will be executed by WordPress on uninstall.
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  1. 1m 49s
    1. Welcome
      1m 16s
    2. Using the exercise files
      33s
  2. 23m 29s
    1. WordPress overview
      2m 32s
    2. Installing WPI for Windows
      3m 42s
    3. Installing MAMP for the Mac
      3m 25s
    4. Installing and configuring WordPress
      5m 51s
    5. Comparing WordPress 3.0 with previous versions
      2m 57s
    6. Setting up a PHP/WordPress development environment
      5m 2s
  3. 14m 47s
    1. Exploring WordPress plugins
      3m 42s
    2. Administering plugins from the WordPress admin
      5m 23s
    3. Exploring where plugins reside
      2m 51s
    4. Introduction to hooks
      2m 51s
  4. 39m 28s
    1. Creating the plugin PHP file(s)
      3m 12s
    2. More on hooks: Actions and filters
      3m 15s
    3. Installation and activation
      4m 6s
    4. Writing activation code
      3m 45s
    5. Writing an action
      5m 12s
    6. Writing a filter
      4m 15s
    7. About pluggable functions
      2m 1s
    8. Writing a pluggable function
      5m 30s
    9. Using template tags
      2m 46s
    10. Introducing shortcode
      5m 26s
  5. 26m 2s
    1. Widgets and the WordPress Widgets SubPanel
      2m 54s
    2. Comparing widgets and plugins
      1m 8s
    3. Using and customizing built-in widgets
      3m 18s
    4. Creating a new widget
      7m 21s
    5. Writing the constructor and registering widgets
      5m 20s
    6. Enabling configuration of widgets
      6m 1s
  6. 44m 59s
    1. Creating an admin interface
      5m 25s
    2. Saving data to the database
      5m 39s
    3. Securing form submission with nonces
      2m 25s
    4. Options editing post-WordPress 2.7
      4m 8s
    5. Integrating with the WordPress admin menus
      3m 34s
    6. WordPress admin dashboard API
      4m 5s
    7. Using existing options and option editing pages in WordPress
      5m 19s
    8. Using jQuery and AJAX for administration
      14m 24s
  7. 27m 13s
    1. Accessing the WordPress database
      5m 45s
    2. Using the built-in schema
      2m 21s
    3. Accessing data using $wpdb
      5m 15s
    4. Creating new tables
      7m 18s
    5. Inserting data
      6m 34s
  8. 26m 27s
    1. Introducing the Loop
      6m 22s
    2. Using WP_Query()
      3m 11s
    3. Custom filtering and sticky posts
      4m 58s
    4. Using jQuery and AJAX for posts and pages
      11m 56s
  9. 12m 9s
    1. Registering and promoting plugins
      2m 28s
    2. Creating an uninstall function
      5m 53s
    3. Backward compatibility issues
      3m 48s
  10. 15m 3s
    1. Understanding security issues
      11m 20s
    2. Internationalizing your plugin
      3m 43s
  11. 18s
    1. Goodbye
      18s

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WordPress: Creating Custom Widgets and Plugins with PHP
3h 51m Intermediate Nov 04, 2010

Viewers: in countries Watching now:

In WordPress: Creating Custom Widgets and Plugins with PHP, Drew Falkman teaches PHP developers how to create custom functionality for WordPress 2.0 through 3.0 using widgets and plugins. This course starts by installing and setting up WordPress 3.0 on both Mac and Windows, then provides an in-depth look at tasks related to these WordPress add-ons: installing and administering, building and customizing, creating editable options and database tables, working with posts and pages, and utilizing jQuery and AJAX. There are also tutorials dedicated to promoting a widget or plugin, adding security, and localizing the interface. Exercise files are included with the course.

Topics include:
  • Installing WPI and MAMP server solutions
  • Administering WordPress plugins
  • Introducing hooks
  • Writing the PHP for a plugin
  • Using template tags and shortcode
  • Building a new widget
  • Creating an admin interface
  • Accessing the WordPress database
  • Using jQuery and AJAX for posts and pages
  • Registering and promoting plugins
Subjects:
Developer Web CMS
Software:
WordPress
Author:
Drew Falkman

Creating an uninstall function

One of the potential problems with open development environments like WordPress is that after a period of time of using plugins that have options from in the database and new database tables, and all this sort of thing, and then deciding not to use them, it's pretty easy to get some database bloat, and have a lot of things hanging out there. So it's a best practice, as plugin developers, to create some sort of uninstall script that removes these items that are plugin uses when they're removed. As of WordPress 2.7, we have a couple of ways to do this. One way is that we can register an uninstall hook, which will essentially set up a function that will be executed by WordPress on uninstall.

The other way is to create an uninstall.php file. Let's go back to our CC comment plugin. If you recall, it set up a specific option called cccomm_cc_e-mail that we use to save the e-mail that the user use. So we want to get rid of this on uninstall. So if you go into your admin, and you go to the options.php page, you can see there's a cccomm_cc_e-mail that's listed there. So let's make sure that gets removed.

The way to do this is you first create a function that is going to do the removing when the uninstall occurs, and to delete an option from the options database, you simply say delete_option, and you pass the name of the option--in this case cccomm_cc_e-mail. You then need to register this, so that when it uninstalls, it will run this function. So we use a special function called register_uninstall_hook.

We're going to specify that it's going to run something in this file, and that the function is going to be cccomm_uninstall. So make sure before you do this that you back up your CC comment. So go into the plugins directory of your WordPress installation, copy the CC comment and put it somewhere-- wherever you like: on your desktop, or in your Documents folder. Just remember where you put it, so you can use it when you go back.

So now let's go ahead and go into our WordPress Administrator. Let's go into the Plugins page, and let's first deactivate our CC Comment plugin and then go ahead and delete it. It's going to give you a confirmation, and you're going to say, "Hmm! Do I want to really delete this?" In this case, we do. So it will have deleted all the files. Let's go into the options.php file again. You'll see now that your CC comments CC e-mail has been deleted. It used to be right about here.

So it did indeed work. So let's go ahead and go back into Eclipse, and you'll see it's giving you information saying these files are no longer there. If you refresh this, you'll see that they are indeed gone. So let's restore from the directory we left it in. So let's go ahead and copy cc_comment. Let's go back into our Plugin directory and paste it again. So now in Eclipse, we can refresh, and we'll see it there. You could also incidentally paste it through this interface, but it's easy enough to do it from within Macintosh or Windows.

So let's go ahead and open this up again, and let's try using the uninstall.php file. The difference is that in order for this to execute, it actually does have to run through the script. There might be something you have going on that you don't want to happen. So the uninstall.php file gives you a very clean uninstall. So let's go ahead and erase this uninstall and save it. And let's right-click on the cc_comment folder and go to New > PHP File, and we'll call it uninstall.php.

We can then paste in our delete_option. There's one other thing you should do: you should make sure that it's not running this somehow from some other way, because you wouldn't want it to delete the option if the user didn't actually want this to be deleted, and it's possible somehow that this PHP file could run. So the best way to do that is to check for the definition of a specific variable. So we'll say if not defined-- and when the uninstall occurs, there is going to be this constant WP_UNINSTALL_PLUGIN.

That's going to exist. So if it doesn't exist, then we can go ahead and just say, "Hey! Stop it." Then we'll exit. So that will then exit this file, and it will stop executing right at that point. However, on uninstall, this will be defined, which means it'll go ahead and go through and execute this line. So if we go back into our Plugins page, we're going to have to reactivate our cc_comment plugin, and let's make sure that that option got added.

It hasn't yet, because we haven't added it. So let's go into the Settings > General, and you can see there's our plugin, enter an e-mail, and then let's go back to the Options page. We should see our e-mail appear here. So now if we go into the uninstall, we deactivate our plugin and we delete it, then we can go back into the Options page, and we should see that our CC comments has been removed.

So since WordPress 2.7, we've had the ability to create uninstall scripts for our plugins. It's considered a best practice to clean up any database tables or any options that you've created in the WordPress database. This is a best practice that keeps our databases clean, and keeps people using plugins.

Find answers to the most frequently asked questions about WordPress: Creating Custom Widgets and Plugins with PHP.


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Q: Do I need a web hosting service for this course?
A: You don't need a hosting site to do any testing or development work that’s covered in this course. However, if you want to have your WordPress site available to the public, you will most definitely need a WordPress site. If you are hosting with an independent company, they will need to have PHP and MySQL installed, and there will be some configuration differences, but basically, you can upload anything on your local version to the web site. If you are hosting with Wordpress.com, you will need to add your plugins by uploading them manually through the WP Admin Plugin screen.
 
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