add_post_meta Adds post meta but the value is blank

Question

My plugin uses a metabox to save post meta. I have three option in the metabox. Everything is saving/updating/deleting correctly except for this:

add_post_meta( $post_id, $meta_key_duration, $new_meta_value_duration, true );

If I echo out the values right before this call:

echo $post_id.' '.$meta_key_duration.' '.$new_meta_value_duration;

I get:

52 expDuration 10

this is correct since I chose "10" as the value to be saved. The database is showing the post_id and meta_id correctly but the value isn't being saved.

Answer 1

If you're updating a value, you want to use update_post_meta. When you set $unique to true in add_post_meta, nothing will happen if the meta key already exists.

Answer 2

Just use update_post_meta() which will make sure that $meta_key already exists. If it does not, add_post_meta is called instead and its result is returned.