編輯“WordPress:Displaying Posts Using a Custom Select Query”

== Description ==
At some point in your WordPress development career you may be presented with the need to display one or more posts using [[WordPress:Wikipedia:SELECT|SELECT]] criteria not provided by WordPress' [[WordPress:Template Tags/query posts | query_posts]] architecture.  For instance, it may become necessary to [[WordPress:Wikipedia:JOIN|JOIN]] WordPress tables to determine which posts should be displayed, or you may want to use data stored in your own tables to determine which [[WordPress:Writing Posts|posts]] should be displayed.

The practical example, outlined below, demonstrates a process of selecting all posts with a particular [[WordPress:Using Custom Fields | Custom Field]] value stored, and displaying them in a [[WordPress:Pages|Page]] based on a [[WordPress:Pages#Creating_your_own_Page_Templates|Page Template]]. Originally, this code was used to implement a post tagging [[WordPress:Plugins|plugin]], which allowed organizing posts in less structured collections than the WordPress [[WordPress:Manage_Categories_SubPanel|Categories]]. Your own usage may be very different, but the content and example should still give you a useful introduction to the general process involved.

=== Assumptions made in this Article ===
Generally, this article assumes you have a working knowledge of [[WordPress:Glossary#PHP|PHP]], [[WordPress:Glossary#MySQL|MySQL]], and WordPress capabilities.

Specific assumptions for the example, however, are:

* You have at least one post with [[WordPress:Using Custom Fields | Custom Fields]] data.  The Custom Fields should have a key of 'tag' and a value of 'email'
* You have created a [[WordPress:Pages|Page]] and associated a [[WordPress:Pages#Page_Templates|Page Template]] with that page.  For this example, assume the Template Name is 'Qbased' and was copied from the ''wp-content/themes/index.php'' template.  If you are not familiar with this process, follow the instructions in [[WordPress:Pages#Creating_your_own_Page_Templates|Creating your own Page Templates]].
* As this is a somewhat advanced developer topic, familiarity with the core WordPress concept of [[WordPress:The Loop]] is suggested. 
 
== Code for the Page Template ==
===The query===
To begin with, it is necessary to retrieve the [[WordPress:Glossary#Recordset|recordset]] containing the posts you want to display.  To do this, create a result set using the WordPress [[WordPress:Function_Reference/wpdb_Class|$wpdb database class]].  Note that the [[WordPress:Glossary#MySQL|MySQL]] [[WordPress:Wikipedia:SELECT|SELECT]] statement illustrates a '''simple''' [[WordPress:Wikipedia:JOIN|JOIN]].  Here, <tt>$pageposts</tt> will contain an [[WordPress:Glossary#Array|array]] of objects. Each object will represent a '''published''' post that has custom field key-value pair - with the key being 'tag' and the value being 'email':
<pre>
 <?php

 $querystr = "
    SELECT wposts.* 
    FROM $wpdb->posts wposts, $wpdb->postmeta wpostmeta
    WHERE wposts.ID = wpostmeta.post_id 
    AND wpostmeta.meta_key = 'tag' 
    AND wpostmeta.meta_value = 'email' 
    AND wposts.post_status = 'publish' 
    AND wposts.post_type = 'post' 
    ORDER BY wposts.post_date DESC
 ";

 $pageposts = $wpdb->get_results($querystr, OBJECT);
 
 ?>
</pre>

===The Revised Loop===
Now, to display posts collected into <tt>$pageposts</tt> by the previous [[WordPress:Wikipedia:SELECT|SELECT]] criteria, you need to replace [[WordPress:The Loop]] with your own loop code in the ''Qbased'' Page Template.  This requires creating a revised loop that cycles through the posts stored in <tt>$pageposts</tt> and displays them. Note: the structure / markup in the loop below is taken from the WordPress '''default''' [[WordPress:Using Themes|theme]].

<pre>
 <?php if ($pageposts): ?>
 <?php foreach ($pageposts as $post): ?>
 <?php setup_postdata($post); ?>
 
 <div class="post" id="post-<?php the_ID(); ?>">
 <h2><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title(); ?>">
    <?php the_title(); ?></a></h2>
    <small><?php the_time('F jS, Y') ?> <!-- by <?php the_author() ?> --></small>
    <div class="entry">
       <?php the_content('Read the rest of this entry &raquo;'); ?>
    </div>
    <p class="postmetadata">Posted in <?php the_category(', ') ?> | <?php edit_post_link('Edit', '', ' | '); ?>  
    <?php comments_popup_link('No Comments &#187;', '1 Comment &#187;', '% Comments &#187;'); ?></p>
 </div>
 <?php endforeach; ?>
 <?php else : ?>
    <h2 class="center">Not Found</h2>
    <p class="center">Sorry, but you are looking for something that isn't here.</p>
    <?php include (TEMPLATEPATH . "/searchform.php"); ?>
 <?php endif; ?>
</pre>

And that's it!

To go through the important parts of the code, line by line, you have:

* A test to make sure that the query that populated <tt>$pageposts</tt> actually found some posts that matched the [[WordPress:Wikipedia:SELECT|SELECT]] criteria:
<pre>
<?php if ($pageposts): ?>
</pre>
* A [[WordPress:Wikipedia:Foreach|foreach loop]] to go through the posts returned in <tt>$pageposts</tt> and display them:
<pre>
<?php foreach($pageposts as $post): ?>
</pre>

* And, a call to the WordPress post formatting function, <tt>setup_postdata()</tt>, that automatically populates the required variables: 
<pre>
<?php setup_postdata($post); ?>
</pre>

==== Within the Loop ====
Because <tt>setup_postdata($post);</tt> was called in our example, you can use the same [[WordPress:Template Tags | template tags]] that can be included in a normal WordPress post loop, like <tt>the_content()</tt> and <tt>the_permalink()</tt>. This means that you can create your own post display results using a Page Template with a minimum amount of fuss, automatically taking advantage of the various plugins you may have activated in your WordPress blog to provide extra formatting and functionality.

=== The Completed Page Template ===
Here is a complete example of the new template that works with the WordPress '''default''' theme.
<pre>
<?php
/*
Template Name: Qbased
*/
?>

<?php get_header(); ?>

<div id="content" class="narrowcolumn">

<?php

 $querystr = "
    SELECT wposts.* 
    FROM $wpdb->posts wposts, $wpdb->postmeta wpostmeta
    WHERE wposts.ID = wpostmeta.post_id 
    AND wpostmeta.meta_key = 'tag' 
    AND wpostmeta.meta_value = 'email' 
    AND wposts.post_status = 'publish' 
    AND wposts.post_type = 'post' 
    AND wposts.post_date < NOW() 
    ORDER BY wposts.post_date DESC
 ";

 $pageposts = $wpdb->get_results($querystr, OBJECT);

?>
 <?php if ($pageposts): ?>
  <?php foreach ($pageposts as $post): ?>
    <?php setup_postdata($post); ?>

    <div class="post" id="post-<?php the_ID(); ?>">
      <h2><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title(); ?>">
      <?php the_title(); ?></a></h2>
      <small><?php the_time('F jS, Y') ?> <!-- by <?php the_author() ?> --></small>
      <div class="entry">
         <?php the_content('Read the rest of this entry ?'); ?>
      </div>
  
      <p class="postmetadata">Posted in <?php the_category(', ') ?> | <?php edit_post_link('Edit', '', ' | '); ?>  
      <?php comments_popup_link('No Comments ?', '1 Comment ?', '% Comments ?'); ?></p>
    </div>
  <?php endforeach; ?>
  
  <?php else : ?>
    <h2 class="center">Not Found</h2>
    <p class="center">Sorry, but you are looking for something that isn't here.</p>
    <?php include (TEMPLATEPATH . "/searchform.php"); ?>
 <?php endif; ?>

</div>

<?php get_sidebar(); ?>

<?php get_footer(); ?>
</pre>
It is important to note here that the above example will work '''only''' when OBJECT is passed as the "output_type" parameter for <code>$wpdb->get_results()</code>. setup_postdata() does not seem to work when ARRAY_A or ARRAY_N is passed in $wpdb->get_results().
==Query based on Custom Field and Category==
This next example sets the $querystr variable used in the above example, to get all posts in Categories 1,2, and 3, that have the meta_key 'paragraf', and then sorted ascending by the meta_values.  This example gleaned from Otto42's response in [http://wordpress.org/support/topic/121011 Forum Topic 121011].
<pre>
 $querystr = "
    SELECT $wpdb->posts.*
    FROM $wpdb->posts
    LEFT JOIN $wpdb->postmeta ON ($wpdb->posts.ID = $wpdb->postmeta.post_id)
    LEFT JOIN $wpdb->post2cat ON ($wpdb->posts.ID = $wpdb->post2cat.post_id)
    WHERE $wpdb->postmeta.meta_key = 'paragraf'
    AND $wpdb->posts.post_status = 'publish'
    AND $wpdb->posts.post_type = 'post'
    AND $wpdb->post2cat.category_id IN (1,2,3)
    ORDER BY $wpdb->postmeta.meta_value ASC
    ";

</pre>



'''with wordpress 2.3 you need to update the sql query shown above to this:'''
This example gleaned from kernow's response in [http://wordpress.org/support/topic/121011 Forum Topic 121011]

<pre>
SELECT * FROM $wpdb->posts
LEFT JOIN $wpdb->postmeta ON($wpdb->posts.ID = $wpdb->postmeta.post_id)
LEFT JOIN $wpdb->term_relationships ON($wpdb->posts.ID = $wpdb->term_relationships.object_id)
LEFT JOIN $wpdb->term_taxonomy ON($wpdb->term_relationships.term_taxonomy_id = $wpdb->term_taxonomy.term_taxonomy_id)
WHERE $wpdb->term_taxonomy.term_id = 1,2,3
AND $wpdb->term_taxonomy.taxonomy = 'category'
AND $wpdb->posts.post_status = 'publish'
AND $wpdb->postmeta.meta_key = 'paragraf'
ORDER BY $wpdb->postmeta.meta_value ASC
</pre>

== Acknowledgements ==

Many thanks to [http://wordpress.org/support/profile/6445 Kafkaesquii] for pointing out a simpler method of populating the appropriate global variables, etc, using setup_postdata().