我found this bit of very useful code用于生成一个下拉列表，以用作多个自定义分类法的URL查询字符串。
下面的代码与if(isset($_GET['taxonomies']))文件中的PHP中的if(empty($_GET['taxonomies']))和archive.php声明配对，可以过滤三种自定义分类法中的信息。
但是，它仅在URL查询参数不为空时才有效。例如：
example.com/custom-post-type-slug/?taxonomy1=term1&taxonomy2=termA&taxonomy3=termZ
...工作正常。
example.com/custom-post-type-slug/?taxonomy1=term1&taxonomy2=termA
...也可以。
但是，下面的代码创建的下拉列表将生成一个URL查询字符串，其中包含空查询参数，例如：
example.com/custom-post-type-slug/?taxonomy1=term1&taxonomy2=&taxonomy3=termZ
分类法2的空查询参数将其破坏。缺少所有查询参数：
example.com/custom-post-type-slug/?taxonomy1=&taxonomy2=&taxonomy3=
如果没有值，如何调整下面的代码以删除URL查询参数？
最理想的情况是，如果没有URL查询值，则从字符串中删除查询参数。如何使用此代码执行此操作？
这是在我的functions.php文件中。
function get_terms_dropdown_taxonomy1($taxonomies, $args){
$myterms = get_terms($taxonomies, $args);
$output ="<select name='taxonomy1'>";
$output .="<option value=''>All Taxonomy 1</option>";
foreach($myterms as $term){
$root_url = get_bloginfo('url');
$term_taxonomy=$term->taxonomy;
$term_slug=$term->slug;
$term_name =$term->name;
$link = $term_slug;
$output .="<option value='".$link."'>".$term_name."</option>";
}
$output .="</select>";
return $output;
}
function get_terms_dropdown_taxonomy2($taxonomies, $args){
$myterms = get_terms($taxonomies, $args);
$output ="<select name='taxonomy2'>";
$output .="<option value=''>All Taxonomy 2</option>";
foreach($myterms as $term){
$root_url = get_bloginfo('url');
$term_taxonomy=$term->taxonomy;
$term_slug=$term->slug;
$term_name =$term->name;
$link = $term_slug;
$output .="<option value='".$link."'>".$term_name."</option>";
}
$output .="</select>";
return $output;
}
function get_terms_dropdown_taxonomy3($taxonomies, $args){
$myterms = get_terms($taxonomies, $args);
$output ="<select name='taxonomy3'>";
$output .="<option value=''>All Taxonomy 3</option>";
foreach($myterms as $term){
$root_url = get_bloginfo('url');
$term_taxonomy=$term->taxonomy;
$term_slug=$term->slug;
$term_name =$term->name;
$link = $term_slug;
$output .="<option value='".$link."'>".$term_name."</option>";
}
$output .="</select>";
return $output;
}
同时，这是在模板文件中输出的。
<?php
$taxonomies = array('taxonomy1');
$args = array('orderby'=>'name','hide_empty'=>1);
$select = get_terms_dropdown_taxonomy1($taxonomies, $args);
$select = preg_replace("#<select([^>]*)>#", "<select$1 id='taxonomy1' class='dropdown' aria-label='Select a taxonomy 1'>", $select);
echo $select;
?>
<?php
$taxonomies = array('taxonomy2');
$args = array('orderby'=>'name','hide_empty'=>1);
$select = get_terms_dropdown_taxonomy2($taxonomies, $args);
$select = preg_replace("#<select([^>]*)>#", "<select$1 id='taxonomy2' class='dropdown' aria-label='Select a taxonomy 2'>", $select);
echo $select;
?>
<?php
$taxonomies = array('taxonomy3');
$args = array('orderby'=>'name','hide_empty'=>1);
$select = get_terms_dropdown_taxonomy3($taxonomies, $args);
$select = preg_replace("#<select([^>]*)>#", "<select$1 id='taxonomy3' class='dropdown' aria-label='Select a taxonomy 3'>", $select);
echo $select;
?>
编辑：感谢您的帮助，这里是最终的工作代码。
<?php
$url = parse_url($_SERVER['REQUEST_URI']);
// WORKING | all taxonomy1, taxonomy2, and taxonomy3; no values for any taxonomy; displays six most recent posts
if(empty($_GET['taxonomy1']) && empty($_GET['taxonomy2']) && empty($_GET['taxonomy3'])) {
$paged = ( get_query_var( 'paged' ) ) ? absint( get_query_var( 'paged' ) ) : 1; $exec_query = new WP_Query( array (
'post_type' => 'custom_post_type',
'publish_status' => 'publish',
'posts_per_page' => 6,
'paged' => $paged,
) );
}
// WORKING | taxonomy1 only; no values for taxonomy2 or taxonomy3
elseif(empty($_GET['taxonomy2']) && empty($_GET['taxonomy3'])) {
$paged = ( get_query_var( 'paged' ) ) ? absint( get_query_var( 'paged' ) ) : 1; $exec_query = new WP_Query( array (
'post_type' => 'custom_post_type',
'publish_status' => 'publish',
'posts_per_page' => 6,
'paged' => $paged,
'tax_query' => array(
array(
'taxonomy' => 'taxonomy1',
'field' => 'slug',
'terms' => $_GET['taxonomy1'],
'operator' => 'IN',
),
),
) );
}
// WORKING | issue only; no values for taxonomy1 or taxonomy3; displays six most recent taxonomy2 posts
elseif(empty($_GET['taxonomy1']) && empty($_GET['taxonomy3'])) {
$paged = ( get_query_var( 'paged' ) ) ? absint( get_query_var( 'paged' ) ) : 1; $exec_query = new WP_Query( array (
'post_type' => 'custom_post_type',
'publish_status' => 'publish',
'posts_per_page' => 6,
'paged' => $paged,
'tax_query' => array(
array(
'taxonomy' => 'taxonomy2',
'field' => 'slug',
'terms' => $_GET['taxonomy2'],
'operator' => 'IN',
),
),
) );
}
// WORKING | taxonomy3 only; no values for taxonomy1 or taxonomy2
elseif(empty($_GET['taxonomy1']) && empty($_GET['taxonomy2'])) {
$paged = ( get_query_var( 'paged' ) ) ? absint( get_query_var( 'paged' ) ) : 1; $exec_query = new WP_Query( array (
'post_type' => 'custom_post_type',
'publish_status' => 'publish',
'posts_per_page' => 6,
'paged' => $paged,
'tax_query' => array(
array(
'taxonomy' => 'taxonomy3',
'field' => 'slug',
'terms' => $_GET['taxonomy3'],
'operator' => 'IN',
),
),
) );
}
// WORKING | taxonomy2 in taxonomy3; no values for taxonomy1
elseif(empty($_GET['taxonomy1'])) {
$paged = ( get_query_var( 'paged' ) ) ? absint( get_query_var( 'paged' ) ) : 1; $exec_query = new WP_Query( array (
'post_type' => 'custom_post_type',
'publish_status' => 'publish',
'posts_per_page' => 6,
'paged' => $paged,
'tax_query' => array(
'relation' => 'AND',
array(
'taxonomy' => 'taxonomy2',
'field' => 'slug',
'terms' => $_GET['taxonomy2'],
'operator' => 'IN',
),
array(
'taxonomy' => 'taxonomy3',
'field' => 'slug',
'terms' => $_GET['taxonomy3'],
'operator' => 'IN',
),
),
) );
}
// WORKING | taxonomy1 in taxonomy3; no values for taxonomy2
elseif(empty($_GET['taxonomy2'])) {
$paged = ( get_query_var( 'paged' ) ) ? absint( get_query_var( 'paged' ) ) : 1; $exec_query = new WP_Query( array (
'post_type' => 'custom_post_type',
'publish_status' => 'publish',
'posts_per_page' => 6,
'paged' => $paged,
'tax_query' => array(
'relation' => 'AND',
array(
'taxonomy' => 'taxonomy1',
'field' => 'slug',
'terms' => $_GET['taxonomy1'],
'operator' => 'IN',
),
array(
'taxonomy' => 'taxonomy3',
'field' => 'slug',
'terms' => $_GET['taxonomy3'],
'operator' => 'IN',
),
),
) );
}
// WORKING | taxonomy1 on taxonomy2; no values for taxonomy3
elseif(empty($_GET['taxonomy3'])) {
$paged = ( get_query_var( 'paged' ) ) ? absint( get_query_var( 'paged' ) ) : 1; $exec_query = new WP_Query( array (
'post_type' => 'custom_post_type',
'publish_status' => 'publish',
'posts_per_page' => 6,
'paged' => $paged,
'tax_query' => array(
'relation' => 'AND',
array(
'taxonomy' => 'taxonomy1',
'field' => 'slug',
'terms' => $_GET['taxonomy1'],
'operator' => 'IN',
),
array(
'taxonomy' => 'taxonomy2',
'field' => 'slug',
'terms' => $_GET['taxonomy2'],
'operator' => 'IN',
),
),
) );
}
elseif(isset($_GET['taxonomy1']) && ($_GET['taxonomy2']) && ($_GET['taxonomy3'])) {
$paged = ( get_query_var( 'paged' ) ) ? absint( get_query_var( 'paged' ) ) : 1; $exec_query = new WP_Query( array (
'post_type' => 'custom_post_type',
'publish_status' => 'publish',
'posts_per_page' => 6,
'paged' => $paged,
'tax_query' => array(
'relation' => 'AND',
array(
'taxonomy' => 'taxonomy1',
'field' => 'slug',
'terms' => $_GET['taxonomy1'],
'operator' => 'IN',
),
array(
'taxonomy' => 'taxonomy2',
'field' => 'slug',
'terms' => $_GET['taxonomy2'],
'operator' => 'IN',
),
array(
'taxonomy' => 'taxonomy3',
'field' => 'slug',
'terms' => $_GET['taxonomy3'],
'operator' => 'IN',
),
),
) );
}
else{
$paged = ( get_query_var( 'paged' ) ) ? absint( get_query_var( 'paged' ) ) : 1; $exec_query = new WP_Query( array (
'post_type' => 'custom_post_type',
'publish_status' => 'publish',
'posts_per_page' => 6,
'paged' => $paged,
) );
}
if ( $exec_query->have_posts() ) { ?><?php while ( $exec_query->have_posts() ): $exec_query->the_post(); ?>
答案 0 :(得分：2)
isset()将返回true。听起来您的代码假设如果该参数存在，它也包含一些有用的值。 isset()不会检查。
在这种情况下，the empty() function可能就是您想要的。如果变量不不存在或者它包含false-y值（例如您要获取的空字符串），则会返回true。
将if语句更改为if (!empty($_GET['taxonomies']))应该可以解决问题。
请记住，字符串"0"也被认为是false-y，因此也被认为是“空”，因此，如果这是您的查询参数之一的有效值，则需要对此进行显式检查。
答案 1 :(得分：0)
为说明@rickdenhaan所说的内容，下面是一些示例：
// Check if $variable is empty, using empty($variable)
$variable = ""; // true
$variable = " "; // false
$variable = 0; // true
$variable = 1; // false
$variable = null; // true
$variable = false; // true
// Check if $variable was defined, using isset($variable)
$variable = ""; // true
$variable = " "; // true
$variable = 0; // true
$variable = 1; // true
$variable = null; // false
$variable = false; // true
好奇心：
如文档中所述，empty()函数实际上是：
(!isset($variable) || $variable == false)