Only a part of array is stored in transient – what could be causing this?

Question

I have created an autosuggest array that I want to store in a transient. My code looks like this:

<?php
// Get any existing copy of our transient data
$suggest = get_transient('suggest');
if ( false === ( $suggest = get_transient( 'suggest' ) ) ) {
        // It wasn't there, so regenerate the data and save the transient
        $suggest = array();
        // We will loop a custom post type and fetch custom meta from each post to be added into the autosuggest array
        $query = new WP_Query( array( 'post_type' => 'my_custom_post_type', 'posts_per_page' => -1, ) );
        $posts = $query->posts;
            foreach($posts as $post) {
                $value1 = get_post_meta( get_the_ID() , '_town', true );
                $value2 = get_post_meta( get_the_ID() , '_quarteroftown', true );
                $value3 = get_post_meta( get_the_ID() , '_street_name', true );
                $value4 = get_post_meta( get_the_ID() , '_supplier_postcode', true );
                if (!in_array($value1, $suggest))
                    {
                        $suggest[] = $value1; 
                    }
                if (!in_array($value2, $suggest))
                    {
                        $suggest[] = $value2; 
                    }
                if (!in_array($value3, $suggest))
                    {
                        $suggest[] = $value3; 
                    }
                if (!in_array($value4, $suggest))
                    {
                        $suggest[] = $value4; 
                    }
                }
        set_transient( 'suggest', $suggest, HOUR_IN_SECONDS );
}; ?>

If I do not set a transient and simply use the $suggest object, all values are properly there in the array. When I add the transient functionality as seen above, the transient will only have $value1 and $value2 strings in it, none of _streetname or _supplier_postcode.

Further fuel to my wtf-fire: if I simply order the transient to be deleted every time, it starts working! See code below:

<?php
    // Get any existing copy of our transient data
    delete_transient('suggest'); // ADDING THIS AND FORCING REGEN OF TRANSIENT EVERY TIME FIXES THE PROBLEM!
    $suggest = get_transient('suggest');

I am at a loss. What on earth can be causing this behaviour?

Answer 1

You are using get_the_id() template tag without proper loop.

Your code should be something like this

<?php
// Get any existing copy of our transient data
$suggest = get_transient('suggest');
if ( false === ( $suggest = get_transient( 'suggest' ) ) ) {
        // It wasn't there, so regenerate the data and save the transient
        $suggest = array();
        // We will loop a custom post type and fetch custom meta from each post to be added into the autosuggest array
        $query = new WP_Query( array( 'post_type' => 'my_custom_post_type', 'posts_per_page' => -1, ) );
        $posts = $query->posts;
            foreach($posts as $the_post) {
                $value1 = get_post_meta( $the_post->ID , '_town', true );
                $value2 = get_post_meta( $the_post->ID , '_quarteroftown', true );
                $value3 = get_post_meta( $the_post->ID , '_street_name', true );
                $value4 = get_post_meta( $the_post->ID , '_supplier_postcode', true );

                if (!in_array($value1, $suggest))
                    {
                        $suggest[] = $value1; 
                    }
                if (!in_array($value2, $suggest))
                    {
                        $suggest[] = $value2; 
                    }
                if (!in_array($value3, $suggest))
                    {
                        $suggest[] = $value3; 
                    }
                if (!in_array($value4, $suggest))
                    {
                        $suggest[] = $value4; 
                    }
                }
        set_transient( 'suggest', $suggest, HOUR_IN_SECONDS );
}; ?>

Answer 2

There is an issue with your code. You are querying the posts, and looping through them without setting the global $post variable. In this kind of loops you can't use get_the_ID() function, as it will return the ID of the currently global $post variable which in your case could be anything, depending on the context of your code.

See the difference:

$query = new WP_Query( [ 'post_type' => 'my_custom_post_type', 'posts_per_page' => - 1, ] );

// First case
if ($query->have_posts()) {
    while($query->have_posts()) {
        // This actually sets the global $post variable to the current post in the loop
        $query->the_post();

        // Here you can use context-dependable functions
        $ID = get_the_ID();
        $title = get_the_title();
    }
}

// You should reset the globals to the previous state
wp_reset_query();

// The Second case
// Please don't use $post variable in your loops, it can sometimes interfere
// with the global $post variable
$my_posts = $query->get_posts();
foreach ($my_posts as $my_post) {
    // here $post is not the global variable, so we can't use the same functions
    $ID = $my_post->ID;
    $title = $my_post->post_title;
}

You can read more about the WP_Query on the WP official documentation.