Sum custom post meta values - php

Question

This should be really straightforward..
I have a custom post type: "shipment" with a custom field "shipment_cost"
I want to sum the total cost of all shipments.
I've managed to get it to output the correct amount with a single post:
$totalcost = 0;
$post_ids = [2583];
foreach( $post_ids as $post_id )
{
$totalcost += (int) get_post_meta( $post_id, 'shipment_cost', true );
}
echo $totalcost;
But when I try to use all shipment CPTs in an array, I get a result of zero.
$shipments = array(
'post_type' => 'shipment'
);
$totalcost = 0;
$post_ids = $shipments;
foreach( $post_ids as $post_id )
{
$totalcost += (int) get_post_meta( $post_id, 'shipment_cost', true );
}
echo $totalcost;
Is my shipments array wrong, or am I just going about this the wrong way in general?
Thanks!

Answer 1

Right now it seems that you are using $shipments as it was an array of post ids? You first need to retrieve all post ids:
$shipments = get_posts(array(
'post_type' => 'shipment',
'post_status' => 'publish'
));
Since the above would return post object you need to modify your loop:
foreach ($shipments as $post) {
$totalcost += (int) get_post_meta($post->ID, 'shipment_cost', true);
}
A better and faster way might be to use a raw database query to get the sum for all meta values:
$totalcost = $wpdb->get_col("SELECT SUM(pm.meta_value) FROM {$wpdb->postmeta} pm
INNER JOIN {$wpdb->posts} p ON p.ID = pm.post_id
WHERE pm.meta_key = 'shipment_cost'
AND p.post_status = 'publish'
AND p.post_type = 'shipment'");

Answer 2

This just saved my life!! Been looking for a solution to total inputs from a Pods Custom Post Type which has a Custom Field that users can enter a number into. I then wrapped the code in a shortcode to display on front end
function jobs_shortcode () {
$jobs = get_posts(array(
'post_type' => 'pledged_job',
'post_status' => 'publish'
));
$total = 0;
$post_ids = $jobs;
foreach ($jobs as $post) {
$total += (int) get_post_meta($post->ID, 'jobs_pledged', true);
}
echo $total;
}
add_shortcode( 'jobs', 'jobs_shortcode' );
THANK YOU!