I believe this was my solution to a previous question you had.
I mentioned in that answer that the code didn’t deal with the eventuality of a key with multiple values and only some of which are empty. The reason why is how WordPress treats delete_post_meta…
When using delete_post_meta, the first two arguments specify the post and the key of the custom field. You have a third optional argument, which can be used to specify a key-value pair. So…
//Delete all post meta with key $key
delete_post_meta($post_id,$key)
//Delete all post meta with key $key AND value $value
delete_post_meta($post_id,$key,$value)
The problem is that if $value is empty it treats it like the first case and deletes all post meta for that post and key.
There is a workaround (and perhaps a non-WordPress based one would be more efficient here), the logic is as follows;
- Identify a key with an empty-value
- Retrieve all non-empty values
- Delete the key
- Re-insert the key, adding only non-empty values
The edited foreach loop;
foreach($custom_fields as $key=>$values):
//$values is an array of values associated with $key - even if there is only one value.
//Filter to remove empty values.
//Be warned this will remove anything that casts as false, e.g. 0 or false
//- if you don't want this, specify a callback.
//See php documentation on array_filter
$nonemptyvalues = array_filter($values);
//If the $nonemptyvalues doesn't match $values then we removed an empty value(s).
if($nonemptyvalues!=$values):
//delete key
delete_post_meta($post_id,$key);
//re-add key and insert only non-empty values
foreach($nonemptyvalues as $nonemptyvalue){
add_post_meta($post_id,$key,$nonemptyvalue);
}
endif;
endforeach;
The above is untested