将 mysql_fetch 数组转换为 $wpdb-> 在 WP Shortcode 中获取结果时出现问题

Question

I am looking to deliver a dropdown within the page of a Wordpress Theme connecting to the backend WP Database using $wpdb and ob_start to bring through option values.

In order to do this I have had to convert mysql_fetch array to $wpdb->get results and use a Shortcode generated from a PHP Snippet plugin.

Code -

add_shortcode( 'get-city', function () {
    ob_start(); ?>
   <?php
    global $wpdb;
    $results = $wpdb->query("SELECT countryid FROM {$wpdb->prefix}city");?>
    <select name="city"> 
    <option>Select City</option> 
    <?php while($row=$wpdb->get_results($results)) {
           echo "<option value>{$row->city}</option>";
    }
    echo "</select>";
    
    return ob_get_clean();
});

The shortcode shows no errors and is able to be activated.

The dropdown shows on the page but then no options are presented for a user to select. Nothing is being brought through from the db.

I would really appreciate it if someone could point out the error.

Thanks in advance.

UPDATE -

I have amended 'while' to 'foreach' within the code -

add_shortcode( 'get-city', function () {
    ob_start(); ?>
   <?php
    global $wpdb;
    $results = $wpdb->query("SELECT city FROM {$wpdb->prefix}city");?>
    <select name="city"> 
    <option>Select City</option> 
    <?php $rows = $wpdb->get_results($results); foreach( $rows as $row ){
           echo "<option value>{$rows->city}</option>";
    }
    echo "</select>";
    
    return ob_get_clean();
});

I still cannot bring values from the backend db.

Many thanks for your response(s) so far.

Answer 1

$wpdb->get_results($results) is basically a fetchAll

https://developer.wordpress.org/reference/classes/wpdb/get_results/

So do this

add_shortcode( 'get-city', function () {
    ob_start(); 

    global $wpdb;
    $results = $wpdb->query("SELECT city FROM {$wpdb->prefix}city");
?>
    <select name="city"> 
        <option>Select City</option> 
<?php 
    $rows = $wpdb->get_results($results); 
    foreach( $rows as $row ){
        echo "<option value='{$row->city}'>{$row->city}</option>";
    }
    echo "</select>";
    
    return ob_get_clean();
});

You may want to put the id of the ciry row in the value attribute like this. Depends on how its stored and later used

echo "<option value='{$row->id}'>{$row->city}</option>";