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

== 描述 ==
在你的WordPress發(fā)展歷程的某個時(shí)刻，或許你需要通過非WordPress的[[WordPress:Template Tags/query posts | query_posts]] 架構(gòu)提供的[[WordPress:Wikipedia:SELECT|選擇]]標(biāo)準(zhǔn)來顯示一篇或更多的文章。例如，你有時(shí)或許必須[[WordPress:Wikipedia:JOIN|加入]] WordPress表格以確定要顯示的文章或使用自己表格中的儲存數(shù)據(jù)來確定要顯示[[WordPress:Writing Posts|正在寫的文章]]。

以下概述的實(shí)例展示了這樣一個過程：選擇有[[WordPress:Using Custom Fields | 定制區(qū)域]]存入值的所有文章并把它們在建立在[[WordPress:Pages#Creating_your_own_Page_Templates|頁面模板]]基礎(chǔ)上的[[WordPress:Pages|頁面]]顯示出來。這些編碼最初用來執(zhí)行文章標(biāo)簽[[WordPress:Plugins|插件]]，它允許以比WordPress[[WordPress:Manage_Categories_SubPanel|分類]]稍無序的構(gòu)架來組織文章。你的使用或許有所不同，但以下的例子仍會給你提供些有用的一般過程說明。

=== 文章假設(shè) ===

本文通常假設(shè)你擁有[[WordPress:Glossary#PHP|PHP]], [[WordPress:Glossary#MySQL|MySQL]]知識和WordPress 使用能力。

但此例的特定假設(shè)是：
*你至少擁有一篇[[WordPress:Using Custom Fields |定制區(qū)域]]數(shù)據(jù)文章。自定義區(qū)域有“標(biāo)簽”鍵和“電子郵件”鍵值。

*你已創(chuàng)建一個[[WordPress:Pages|頁面]]并有一個[[WordPress:Pages#Page_Templates|頁面模板]]鏈接。在此例中，假定模板名稱為'Qbased'，它是從wp-content/themes/index.php模板復(fù)制的。如果你對此過程不熟悉，按照[[WordPress:Pages#Creating_your_own_Page_Templates|創(chuàng)建你自己的頁面模板]]中的說明進(jìn)行操作。

*由于這是稍先進(jìn)的開發(fā)主題，推薦掌握[[WordPress:The Loop|循環(huán)]]的WordPress核心概念。

== 網(wǎng)頁模板編碼 ==

===查詢===


首先，需要檢索[[WordPress:Glossary#Recordset|數(shù)據(jù)集]，里面包含你要顯示的文章。要做到這一點(diǎn)，需要使用WordPress[[WordPress:Function_Reference/wpdb_Class|$wpdb 數(shù)據(jù)庫 類]]創(chuàng)建一個（結(jié)果集）。注意[[WordPress:Glossary#MySQL|MySQL]] [[WordPress:Wikipedia:SELECT|SELECT]]指令闡明了一個“簡單的” [[WordPress:Wikipedia:JOIN|JOIN]]。<tt>$pageposts</tt>在此會包含[[WordPress:Glossary#Array|數(shù)組]]對象。每個對象代表一篇有自定義字段key-value（鍵-鍵值）配對且鍵名為tag，值為email的“已發(fā)布”文章。


<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>


===已修改的Loop（循環(huán)）===
現(xiàn)在，若要通過以前的[[WordPress:Wikipedia:SELECT|SELECT]] 標(biāo)準(zhǔn)來顯示<tt>$pageposts</tt>中的文章，你需要用Qbased網(wǎng)頁模板中你自己的循環(huán)編碼來替代[[WordPress:The Loop]]。這需要創(chuàng)建一個已修改的循環(huán)（loop），使它能夠循環(huán)<tt>$pageposts</tt>中的文章并顯示它們。注意：下面loop(循環(huán))中的結(jié)構(gòu)/標(biāo)記取自WordPress“默認(rèn)”[[WordPress:Using Themes|主題]].
。

<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>
<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>

就是它！

一行一行地審查編碼的重要部分，你必須：

*測試以確保<tt>$pageposts</tt>中的查詢可以查到符合[[WordPress:Wikipedia:SELECT|SELECT]]標(biāo)準(zhǔn)的文章：

<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 $post): ?>
</pre>
<pre>
<?php if ($pageposts): ?>
</pre>
* A [[WordPress:Wikipedia:Foreach|foreach loop]] to go through the posts returned in <tt>$pageposts</tt> and display them:
*[[WordPress:Wikipedia:Foreach|foreach loop]]審查已返回<tt>$pageposts</tt>的文章，并顯示文章：
<pre>
<?php foreach($pageposts as $post): ?>
</pre>

*調(diào)用WordPress文章格式化函數(shù)，<tt>setup_postdata()</tt>,自動填入所需變量：
<pre>
<?php setup_postdata($post); ?>
</pre>
 	

==== Loop （循環(huán)）內(nèi)部====
由于例子中調(diào)用了<tt>setup_postdata($post);</tt>，你可以使用可包括在正常Wordpress循環(huán)（loop）中的相同[[WordPress:Template Tags |模板標(biāo)簽]]，如<tt>the_content()</tt> 和 <tt>the_permalink()</tt>。這意味著你能夠較方便地用網(wǎng)頁模板創(chuàng)建自己的文章顯示結(jié)果，并自動利用你的Wordpress博客已激活的各種插件提供額外的格式和功能。

===已完成的網(wǎng)頁模板===
這是Wordpress“默認(rèn)”主題運(yùn)行的新模板的完整事例。
<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>

這里值得注意的是，上述例子“只有”當(dāng)<code>$wpdb->get_results()</code>是以"output_type"為參數(shù)，面向?qū)ο笸ㄟ^時(shí)才運(yùn)行。當(dāng)ARRAY_A 或ARRAY_N在$wpdb->get_results()通過時(shí)，setup_postdata()似乎不運(yùn)行。
==定制區(qū)域和類別基礎(chǔ)上的查詢==
此事例設(shè)置了上個事例中使用的$querystr變量以獲得類別1，2，和3中的有meta_key 'paragraf'的所有文章，并按meta_values升序排列。此例來源于Otto42在[http://wordpress.org/support/topic/121011 Forum Topic 121011].
中的回復(fù)。
<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>


'''使用 wordpress2.3，你需要把以上顯示的sql查詢更新為：'''
此例來源于kernow在[http://wordpress.org/support/topic/121011 Forum Topic 121011] 中的回復(fù)


<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>
==致謝 ==
非常感謝[http://wordpress.org/support/profile/6445 Kafkaesquii]指出填寫適當(dāng)全局變量等的更簡便方法：使用setup_postdata()。