Get the correct meta_value with get_post_meta

Question

I tried using the function get_post_meta() to get the meta values of my posts. However to my surprise it returns an Array that contains again arrays! So I looked inside the second level array, and was able to get a list of meta values with this code:

$postmeta = get_post_meta($resultid, '', true);

foreach ($postmeta as $meta_key => $v) {
    foreach ($v as $kk => $meta_value) {
        echo "$meta_key => $meta_value.\n";
    }
}

However, even though I put $single = true reading the documentation here: https://developer.wordpress.org/reference/functions/get_post_meta/
It still gives me 2 values for the same meta key.

E.g. I get this list printed:

select_inco => fob.
select_inco => fob.
price_input_currency => usd.
price_input_currency => usd.
price_input => 58.
price_input_to => .
price_per => .
price_comments => 

My Question:

How do I know what the difference is between these double values like select_inco and price_input_currency and which one is the correct one?

This is how I add and also edit meta_values from a form:

update_post_meta($post_id, 'select_inco', $_POST['select_inco']);

Answer 1

get_post_meta() is simply just a wrapper for get_metadata(). If we look at the source or get_metadata(), we will find that, if $key is left empty, $single is ignored because of the following lines of code which comes before $single is applied

if ( ! $meta_key ) {
    return $meta_cache;
}

So, in your usecase, $single never gets to do it's job.

The double key=>value pairs simply means that you have an array of values for that specific key, and the two values in the array are the same value. This is caused by a flaw somewhere in your code which is responsible for saving data to your custom field. You should go and search for that particular piece of code and sort that particular issue.

I cannot tell you which is the correct value and which not, that is something that you also cannot answer. As I said, you will need to sort your code responsible for saving your custom field data.

In the meantime, you can break out of your foreach loop to only get the first value from a custom field, but I do not recommend this as a solution, the solution will involve to sort how you save your custom field data

$postmeta = get_post_meta($resultid, '', true);

foreach ($postmeta as $meta_key => $v) {
    foreach ($v as $kk => $meta_value) {
        echo "$meta_key => $meta_value.\n";
        break;
    }
}