不确定实施AJAX的想法

Question

I was thinking about how to make an instant messaging application, and wanted to not have to send an AJAX request so often (one every .2s), and I came across the following idea:

1. Send an AJAX request from the user side, to the server.
2. Only respond once there is a change in the MySQL database
3. And then send the next AJAX request once the response has been recorded and parsed

I'm aware of how to do the first and third steps, but the second one is going over my head.

I'm assuming that for step 2, I'll need to store the request somewhere, while the PHP script is continuously looping and looking for some changes, and once there is a change, the saved request would be responded to.

Answer 1

You could use recursion and query the database every 2 seconds, until you find new data to be served to the user. So basically you could do something like

public function isDataUpdated($lastId) {
   $query = "SELECT * FROM `messages` WHERE `messages`.`message_id` > $lastId";
   return (bool)(count($this->executeSQL($query)) > 0);
}

public function fetchNewMessages () {
    if ($this->isDataUpdated($_GET['last_id'])) {
        /* We have new data! Send it to the user */
    } else {
        sleep(2); // wait for 2 seconds
        $this->fetchNewMessages(); // we use recursion to query the database every 2 seconds to find new data
    }
}

Although, it is not the best of solutions, it would hopefully work. I would recommend taking a look at Sockets in PHP to better achieve what you want