(For more resources on WordPress, see here.)

At its most basic, a simple implementation of the loop could work like this:

<?php if (have_posts()) : while (have_posts()) : the_post(); ?>
<?php the_title(); ?>
<?php the_content(); ?>
<?php endwhile; else: ?>
<p>Sorry, no posts matched your criteria.'</p>
<?php endif; ?>

In the real world, however, the WordPress loop is rarely that simple. This is one of those concepts best explained by referring to a real world example, so open up the index.php file of your system's TwentyEleven theme. Look for the following lines of code:

<?php if ( have_posts() ) : ?>
<?php twentyeleven_content_nav( 'nav-above' ); ?>
<?php /* Start the Loop */ ?>
<?php while ( have_posts() ) : the_post(); ?>
<?php get_template_part( 'content', get_post_format()
); ?>
<?php endwhile; ?>
<?php twentyeleven_content_nav( 'nav-below' ); ?>
<?php else : ?>
<article id="post-0" class="post no-results not-found">
<header class="entry-header">
<h1 class="entry-title"><?php _e( 'Nothing Found',
'twentyeleven' ); ?></h1>
</header><!-- .entry-header -->
<div class="entry-content">
3
<p><?php _e( 'Apologies, but no results were found
for the requested archive. Perhaps searching will help
find a related post.', 'twentyeleven' ); ?></p>
<?php get_search_form(); ?>
</div><!-- .entry-content -->
</article><!-- #post-0 -->
<?php endif; ?>

Most of the extra stuff seen in the loop from TwentyEleven is there to add in additional page elements, including content navigation; there's also some code to control what happens if there are no posts to display. The nature of the WordPress loops means that theme authors can add in what they want to display and thereby customize and control the output of their site.

As you would expect, the WordPress Codex includes an extensive discussion of the WordPress loop. Visit http://codex.wordpress.org/The_Loop.

Accessing posts within the WordPress loop

In this recipe, we look at how to create a custom template that includes your own implementation of the WordPress loop.

Getting ready

All you need to execute this recipe is your favorite code editor and access to the WordPress files on your server. You will also need a theme template file, which we will use to hold our modified WordPress loop.

How to do it

Let's assume you have created a custom template. Inside of that template you will want to include the WordPress loop. Follow these steps to add the loop, along with a little customization:

1. Access the active theme files on your WordPress installation.
2. Find a template file and open it for editing. If you're not sure which one to use, try the index.php file.
3. Add to the file the following line of code, which will start the loop:

   <?php if ( have_posts() ) : while ( have_posts() ) : the_post();
   ?>

4. Next, let's display the post title, wrapped in an h2 tag:

   <h2><?php the_title() ?></h2>

5. Let's also add a link to all posts by this author. Add this code immediately below the previous line:

   <?php the_author_posts_link() ?>

6. For the post content, let's wrap it in a div for easy styling:

   <div class="thecontent">
   <?php the_content(); ?>
   </div>

7. Next, let's terminate the loop and add some code to display a message if there were no posts to display:

   <?php endwhile; else: ?>
   <p>Oops! There are no posts to display.</p>

8. Finally, let's put a complete stop to the loop by ending the if statement that began the code in step number 3, above:

   <?php endif; ?>

9. Save the file.

That's all there is to it. Your code should look like this:

?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>
<h2><?php the_title() ?></h2>
<?php the_author_posts_link() ?>
<div class="thecontent">
<?php the_content(); ?>
</div>
<?php endwhile; else: ?>
<p>Oops! There are no posts to display.</p>
<?php endif; ?>

How it works...

This basic piece of code first checks if there are posts in your site. If the answer is yes, the loop will repeat until every post title and their contents are displayed on the page. The post title is displayed using the_title(). The author's name and link are added with the_ author_posts_link() function. The content is displayed with the_content() function and styled by the div named thecontent. Finally, if there are no posts to display, the code will display the message Oops! There are no posts to display.

There's more...

In the preceding code you saw the use of two template tags: the_author_posts_link and the_content. These are just two examples of the many template tags available in WordPress. The tags make your life easier by reducing an entire function to just a short phrase. You can find a full list of the template tags at: http://codex.wordpress.org/ Template_Tags.

The template tags can be broken down into a number of categories:

• General tags: The tags in this category cover general page elements common to most templates
• Author tags: Tags related to author information
• Bookmark tags: The tag to list bookmarks
• Category tags: Category, tag, and item description-related
• Comment tags: Tags covering the comment elements
• Link tags: Tags for links and permalinks
• Post tags: Tags for posts, excerpts, titles, and attachments
• Post Thumbnail tags: Tags that relate to the post thumbnails
• Navigation Menu tags: Tags for the nav menu and menu tree

Retrieving posts from a specific category

There are times when you might wish to display only those posts that belong to a specific category, for example, perhaps you want to show only the featured posts. With a small modification to the WordPress loop, it's easy to grab only those posts you want to display.

In this recipe we introduce query_posts(),which can be used to control which posts are displayed by the loop.

Getting ready

To execute this recipe, you will need a code editor and access to the WordPress files on your server. You will also need a theme template file, which we will use to hold our modified WordPress loop. To keep this recipe short and to the point, we use the loop we created in the preceding recipe.

How to do it...

Let's create a situation where the loop shows only those posts assigned to the Featured category. To do this, you will need to work through two different processes.

First, you need to find the category ID number of the Featured category. To do this, follow these steps:

1. Log in to the Dashboard of your WordPress site.
2. Click on the Posts menu.
3. Click on the Categories option.
4. Click on the category named Featured.
5. Look at the address bar of your browser and you will notice that part of the string looks something like this:&tag_ID=9. On the site where we are working, the Featured category has the ID of 9.

Category IDs vary from site to site. The ID used in this recipe may not be the same as the ID for your site!

Next, we need to add a query to our loop that will extract only those posts that belong to the Featured category, that is, to those posts that belong to the category with the ID of 9. Follow these steps:

1. Open the file that contains the loop. We'll use the same file we created in the preceding recipe.
2. Find the loop:

   <?php if ( have_posts() ) : while ( have_posts() ) :
   the_post(); ?>
   <h2><?php the_title() ?></h2>
   <?php the_author_posts_link() ?>
   <div class="thecontent">
   <?php the_content(); ?>
   </div>
   <?php endwhile; else: ?>
   <p>Oops! There are no posts to display.</p>
   <?php endif; ?>

3. Add the following line of code immediately above the loop:

   <?php query_posts($query_string.'&cat=9'); ?>

4. Save the file.

That's all there is to it. If you visit your site, you will now see that the page displays only the posts that belong to the category with the ID of 9.

How it works...

The query_posts() function modifies the default loop. When used with the cat parameter, it allows you to specify one or more categories that you want to use as filters for the posts.

For example:

• query_posts(&query_string.'&cat=5');: Get posts from the category with ID 5 only
• query_posts(&query_string.'&cat=5,6,9');: Get posts from the category with IDs 5, 6, and 9
• query_posts(&query_string.'&cat=-3');: Get posts from all categories, except those from the category with ID 3

For more information, visit the WordPRess Codex page on query posts: http://codex.wordpress.org/Function_Reference/query_posts