add_metadata( string $meta_type, int $object_id, string $meta_key, mixed $meta_value, bool $unique = false ): int|false

32function add_metadata( $meta_type, $object_id, $meta_key, $meta_value, $unique = false ) {33	global $wpdb;34 35	if ( ! $meta_type || ! $meta_key || ! is_numeric( $object_id ) ) {36		return false;37	}38 39	$object_id = absint( $object_id );40	if ( ! $object_id ) {41		return false;42	}43 44	$table = _get_meta_table( $meta_type );45	if ( ! $table ) {46		return false;47	}48 49	$meta_subtype = get_object_subtype( $meta_type, $object_id );50 51	$column = sanitize_key( $meta_type . '_id' );52 53	// expected_slashed ($meta_key)54	$meta_key   = wp_unslash( $meta_key );55	$meta_value = wp_unslash( $meta_value );56	$meta_value = sanitize_meta( $meta_key, $meta_value, $meta_type, $meta_subtype );57 58	/**59	 * Short-circuits adding metadata of a specific type.60	 *61	 * The dynamic portion of the hook name, `$meta_type`, refers to the meta object type62	 * (post, comment, term, user, or any other type with an associated meta table).63	 * Returning a non-null value will effectively short-circuit the function.64	 *65	 * Possible hook names include:66	 *67	 *  - `add_post_metadata`68	 *  - `add_comment_metadata`69	 *  - `add_term_metadata`70	 *  - `add_user_metadata`71	 *72	 * @since 3.1.073	 *74	 * @param null|bool $check      Whether to allow adding metadata for the given type.75	 * @param int       $object_id  ID of the object metadata is for.76	 * @param string    $meta_key   Metadata key.77	 * @param mixed     $meta_value Metadata value. Must be serializable if non-scalar.78	 * @param bool      $unique     Whether the specified meta key should be unique for the object.79	 */80	$check = apply_filters( "add_{$meta_type}_metadata", null, $object_id, $meta_key, $meta_value, $unique );81	if ( null !== $check ) {82		return $check;83	}84 85	if ( $unique && $wpdb->get_var(86		$wpdb->prepare(87			"SELECT COUNT(*) FROM $table WHERE meta_key = %s AND $column = %d",88			$meta_key,89			$object_id90		)91	) ) {92		return false;93	}94 95	$_meta_value = $meta_value;96	$meta_value  = maybe_serialize( $meta_value );97 98	/**99	 * Fires immediately before meta of a specific type is added.100	 *101	 * The dynamic portion of the hook name, `$meta_type`, refers to the meta object type102	 * (post, comment, term, user, or any other type with an associated meta table).103	 *104	 * Possible hook names include:105	 *106	 *  - `add_post_meta`107	 *  - `add_comment_meta`108	 *  - `add_term_meta`109	 *  - `add_user_meta`110	 *111	 * @since 3.1.0