Difference between last_name and user_lastname

Question

As per documentation, the method get_the_author_meta() has a $field argument with the following possible values:

• admin_color
• aim
• comment_shortcuts
• description
• display_name
• first_name
• ID
• jabber
• last_name
• nickname
• plugins_last_view
• plugins_per_page
• rich_editing
• syntax_highlighting
• user_activation_key
• user_description
• user_email
• user_firstname
• user_lastname
• user_level
• user_login
• user_nicename
• user_pass
• user_registered
• user_status
• user_url
• yim

I wonder, what is the difference between last_name and user_lastname (first_name and user_firstname respectively ).

Which property am I supposed to use and what are possible reasons that one might be filled, while at the same time the other is not?

Answer 1

Short answer to "Which property am I supposed to use": Use first_name and last_name.

Longer answer:

The properties first_name, user_firstname, last_name and user_lastname are defined in the WP_User class, and despite the different names (i.e. one with user_ and the other without that prefix):

• Both first_name and user_firstname use the value of the first_name meta.
• Both last_name and user_lastname use the value of the last_name meta.

But user_firstname and user_lastname were the property names used in WordPress prior to version 2.0.0 (14 years ago..) — see get_the_author_firstname() and get_the_author_lastname() here and here, and that properties are still supported for backward compatibility, but we should just use the ones without the user_ prefix (e.g. first_name and not user_firstname).

// Both of these return the same value - the value of the meta named first_name.
var_dump(
    get_the_author_meta( 'user_firstname' ), // works
    get_the_author_meta( 'first_name' )      // but better
);

// Both of these return the same value - the value of the meta named first_name.
$current_user = wp_get_current_user();
var_dump(
    $current_user->user_firstname, // works
    $current_user->first_name      // but better/shorter...
);