一次奇妙的旅行“cat“

假设我们有以下类别层次结构：

其中wp_term_taxonomy 表包括：

我们想查询动物中的所有帖子category 其中id 是65:

$query = new WP_Query( array( \'cat\' => 65 ) );

并尝试理解为什么生成的SQL是：

SELECT SQL_CALC_FOUND_ROWS  wp_posts.ID 
    FROM wp_posts  
    INNER JOIN wp_term_relationships 
        ON (wp_posts.ID = wp_term_relationships.object_id) 
    WHERE 1=1  
    AND ( wp_term_relationships.term_taxonomy_id IN (15,70, 75) ) 
        AND wp_posts.post_type = \'post\' 
    AND (wp_posts.post_status = \'publish\' OR wp_posts.post_status = \'private\') 
    GROUP BY wp_posts.ID 
    ORDER BY wp_posts.post_date 
    DESC LIMIT 0, 5

即为什么部分65 已更改为15, 70, 75.

Let\'s start:

在里面WP_Query() 我们的查询转换为：

$tax_query[0] = array( \'taxonomy\'           => \'category\',
                       \'terms\'              =>  array( 65 ),
                       \'field\'              => \'term_id\',
                       \'include_children\'   => 1
                   );

在给饥饿的人喂食之前：

 WP_Tax_Query( $tax_query )

它从$tax_query 大堆

在那里，它与默认值合并：

array( \'taxonomy\'          => \'\',
       \'terms\'             => array(),
       \'include_children\'  => true,
       \'field\'             => \'term_id\',
       \'operator\'          => \'IN\',
);

当WP_Query() 对象希望返回生成的SQL查询，它调用WP_TAX_Query::get_sql() 方法

然后我们的阵列被“清理”和“变换”：

a) 它是cleaned 通过WP_TAX_Query::clean_query() 方法，导致：

array( \'taxonomy\'           => \'category\',
       \'terms\'              =>  array( 61, 13, 65 ),
       \'field\'              => \'term_id\',
       \'include_children\'   =>  1,
       \'operator\'           => \'IN\',
);

其中包含子类别get_term_children().

b) 它是transformed 通过WP_TAX_Query::transform_query() 方法，其中term_id 转换为相应的term_taxonomy_id 价值观

在我们的案例中，其结果是：

 SELECT term_taxonomy_id
 FROM wp_term_taxonomy
 WHERE taxonomy = \'category\'
 AND term_id IN (15, 61, 65)

即15, 70 和75:

然后，我们的税务查询如下所示：

array( \'taxonomy\'           => \'category\',
       \'terms\'              =>  array( 15, 70, 75 ),
       \'field\'              => \'term_taxonomy_id\',
       \'include_children\'   =>  1,
       \'operator\'           => \'IN\',
);

在将其添加到的SQL查询部分之前WP_Query():

"join": INNER JOIN wp_term_relationships 
            ON (wp_posts.ID = wp_term_relationships.object_id)

"where": AND ( tfl_term_relationships.term_taxonomy_id IN (15,70,75) ) 

结束；-）

您还可以直接使用WP_TAX_Query 类，以调查生成的SQL。

例如：

    $tax_query = array();
    $tax_query[0] = array(
                   \'taxonomy\'           => \'category\',
                   \'terms\'              =>  array( 65 ),
                   \'field\'              => \'term_id\',
                   \'include_children\'   => 1
               );
    $t = new WP_TAX_Query( $tax_query );
    print_r( $t->get_sql( $GLOBALS[\'wpdb\']->posts, \'ID\' ) );

将给出以下输出：

Array
(
    [join] =>  INNER JOIN wp_term_relationships ON (tfl_posts.ID = wp_term_relationships.object_id)
    [where] =>  AND ( wp_term_relationships.term_taxonomy_id IN (15,70,75) )
)