set_transient( string $transient, mixed $value, int $expiration )

更新瞬时值/a。
Sets/updates the value of a transient.

目录锚点：#说明#参数#源码#笔记

说明（Description）

不需要序列化值。如果需要序列化该值，则在设置之前将其序列化。

参数（Parameters）

源码（Source）

/**
 * Set/update the value of a transient.
 *
 * You do not need to serialize values. If the value needs to be serialized, then
 * it will be serialized before it is set.
 *
 * @since 2.8.0
 *
 * @param string $transient  Transient name. Expected to not be SQL-escaped. Must be
 *                           45 characters or fewer in length.
 * @param mixed  $value      Transient value. Must be serializable if non-scalar.
 *                           Expected to not be SQL-escaped.
 * @param int    $expiration Optional. Time until expiration in seconds. Default 0.
 * @return bool False if value was not set and true if value was set.
 */
function set_transient( $transient, $value, $expiration = 0 ) {

	$expiration = (int) $expiration;

	/**
	 * Filter a specific transient before its value is set.
	 *
	 * The dynamic portion of the hook name, `$transient`, refers to the transient name.
	 *
	 * @since 3.0.0
	 * @since 4.2.0 Added `$expiration` parameter.
	 *
	 * @param mixed $value      New value of transient.
	 * @param int   $expiration Time until expiration in seconds.
	 */
	$value = apply_filters( 'pre_set_transient_' . $transient, $value, $expiration );

	if ( wp_using_ext_object_cache() ) {
		$result = wp_cache_set( $transient, $value, 'transient', $expiration );
	} else {
		$transient_timeout = '_transient_timeout_' . $transient;
		$transient = '_transient_' . $transient;
		if ( false === get_option( $transient ) ) {
			$autoload = 'yes';
			if ( $expiration ) {
				$autoload = 'no';
				add_option( $transient_timeout, time() + $expiration, '', 'no' );
			}
			$result = add_option( $transient, $value, '', $autoload );
		} else {
			// If expiration is requested, but the transient has no timeout option,
			// delete, then re-create transient rather than update.
			$update = true;
			if ( $expiration ) {
				if ( false === get_option( $transient_timeout ) ) {
					delete_option( $transient );
					add_option( $transient_timeout, time() + $expiration, '', 'no' );
					$result = add_option( $transient, $value, '', 'no' );
					$update = false;
				} else {
					update_option( $transient_timeout, time() + $expiration );
				}
			}
			if ( $update ) {
				$result = update_option( $transient, $value );
			}
		}
	}

	if ( $result ) {

		/**
		 * Fires after the value for a specific transient has been set.
		 *
		 * The dynamic portion of the hook name, `$transient`, refers to the transient name.
		 *
		 * @since 3.0.0
		 *
		 * @param mixed $value      Transient value.
		 * @param int   $expiration Time until expiration in seconds. Default 0.
		 */
		do_action( 'set_transient_' . $transient, $value, $expiration );

		/**
		 * Fires after the value for a transient has been set.
		 *
		 * @since 3.0.0
		 *
		 * @param string $transient  The name of the transient.
		 * @param mixed  $value      Transient value.
		 * @param int    $expiration Time until expiration in seconds. Default 0.
		 */
		do_action( 'setted_transient', $transient, $value, $expiration );
	}
	return $result;
}

笔记（Notes）

除非使用外部对象缓存，否则使用set_transient（）更新具有现有过期的现有瞬态时，不提供过期值将保持现有的过期。