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Using WP_Query()

From: WordPress: Creating Custom Widgets and Plugins with PHP

Video: Using WP_Query()

As we've learned, every page in WordPress has its own loop. This contains the data relevant to that page. At some point, we might want to query our own loop and essentially access the same kind of post and page data, but not have it be whatever is on the current page. There's a special class built into WordPress called WP_Query that we can use for this. If you remember, we've built this top_ posts widget, which will output information about each post that's on the current page. So as you can see, on the default page, it's outputting the two items. But if I go to the About page, it outputs the About page itself, which is stored in that loop.

Using WP_Query()

As we've learned, every page in WordPress has its own loop. This contains the data relevant to that page. At some point, we might want to query our own loop and essentially access the same kind of post and page data, but not have it be whatever is on the current page. There's a special class built into WordPress called WP_Query that we can use for this. If you remember, we've built this top_ posts widget, which will output information about each post that's on the current page. So as you can see, on the default page, it's outputting the two items. But if I go to the About page, it outputs the About page itself, which is stored in that loop.

What it's doing is it's calling these methods, have_posts and the_post, on the special default WP_Query class that's built into WordPress. This class gets its data in the header, and it gets it depending on the file you're in and any URL variables that might have been passed to it. If we want to create our own object, we can essentially create a variable and set it equal to the WP_Query class.

This class is made to store this data, and it's much cleaner and easier and better to use than accessing the database directly. So what we do to populate it is we simply call the get_posts method of that object. This will go out and get posts. You can apply filters if you want to, and we'll talk about that later. For now, it's just going to populate it with the default post data, essentially what would display on the first page: any sticky posts and then other posts in descending order.

To output in our loop, we now need to access the post data from this query. So just change it so you are calling the same methods of the query. So now it's getting data from our posts. The post itself will always populate the default post, and that is what's accessible by these template tags. So you don't have to do any changes to the template tags; just make sure you prefix your have_posts and the_post with your specific post object.

So let's go back to our site, and let's go ahead and refresh the homepage. You'll see I have "Update for Today" and "Hello world!" These are the default posts, which is what I'd expect because those are the post available on the main page. However, if I go into the About page, you'll see that I still have the same posts, because it's now getting these posts from our get_posts call. So, WordPress offers us the ability to create our own customized post and page data by using this WP_Query class.

We can then call the get_posts method to populate it, and we loop through it just like we did with the main loop, using have_posts and ultimately setting the post information to the current page by calling the_post.

Show transcript

This video is part of

Image for WordPress: Creating Custom Widgets and Plugins with PHP
 
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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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