操纵MySQL数据库数据

Question

I have a MySQL database that holds a list of classes in columns, and each class has a "level" which is the value of the row, which changes for each person. So, math, for example, has 0, 1, 2, and 3 as possible values, 0 being not selected as a class, and 1, 2, and 3 being high, medium, and low, respectively.

I have a MySQL query which pulls just the classes from a user's database row.

$result = mysql_query("SELECT math, physics, biology, chemistry, english, spanish, history, economics, art, theoryofknowledge, extendedessay FROM users WHERE username = '". $login_session ."'") or die(mysql_error());  

        while($row = mysql_fetch_array( $result )) {
            echo "Math:". $row['math'] ."<br />";
            echo "Physics:". $row['physics'] ."<br />";
            echo "Biology:". $row['biology'] ."<br />";
            echo "Chemistry:". $row['chemistry'] ."<br />";
            echo "English:". $row['english'] ."<br />";
            echo "Spanish:". $row['spanish'] ."<br />";
            echo "History:". $row['history'] ."<br />";
            echo "Economics:". $row['economics'] ."<br />";
            echo "Art:". $row['art'] ."<br />";
            echo "Theory of Knowledge:". $row['theoryofknowledge'] ."<br />";
            echo "Extended Essay:". $row['extendedessay'];
        }

Here is the output for a user:

Math:1
Physics:1
Biology:0
Chemistry:2
English:2
Spanish:3
History:0
Economics:1
Art:0
Theory of Knowledge:1
Extended Essay:1

How could I determine which level a user has, without doing an if statement for every single time the class is called? I need to call the classes in multiple places on the site, and I'd like an easy way to check which classes, and level, the user has.

Thanks!

Answer 1

I think the best approach would be to build a PHP class that loads the user in and inside it have a function that can accept a class (Biology, Math etc) and return the level of the user. If you wanted to, you could write something simple that performs a check of the level required and returns a true or false depending on if the user is a high enough level.

I even slapped together some super basic structure you might want to extend upon:

<?php

    class myUser
    // You are making an object here that stores information about your user.
    // This will mean you only need to query that data once from the DB, then
    // you can use it anywhere on the page without needing to do more queries.
    {
        public $math;
        public $biology;
        // I am making public variables here based on your columns
        // You cuold just as easily make an array for example to store them in.

        public function __construct($userID)
        // Making a construct class - meaning you will be able to write a snippet
        // like this: $currentUser = new myUser(6);
        // and the user information will be loaded nicely for you
        {
            $query="select math, biology from users where ID=$userID";
            // database stuff ....
            // this is where you would write your actual code to get the info
            // from the database and populate it properly, not like I did
            // below for this example
            $this->math=4;
            $this->biology=2;
        }

        public function checkUserLevel($myTopic, $reqLevel)
        // Making use of a few things here that I should ntoe:
        // This is a function you can call from the main code below
        // like this: $currentUser->checkUserLevel('math',3)
        // it will return either true or false.
        // I have used variable variables here for the $myTopic to
        // make it easier. You normally access an element differently
        // normally it is like: echo $this->math;  // output 4
        // Also I am using a ternary operator to return the data,
        // which is just a shortcut.
        {
            return ($this->$myTopic>=$reqLevel)? true : false;
        }

        public function returnUserLevel($myTopic)
        {
            return $this->$myTopic;
        }

    }

    $currentUser = new myUser(6);
    // This is creating a new user object based on the class we made above.
    // Further Explanation:
    // We have a class called myUser, but a class is just a schematic.
    // The $currenUser bit defines a new variable in our code.
    // the "= new myUser" bit says that we want to use the schematic above for this variable
    // the "myUser(6)" basically gives the constructor function an ID to get from
    // the database for the user. Because we defined a constructor class that expects
    // an ID, we need to supply it one, else we will get an error.
    // So $currentUser = new myUser(6)
    // really means "Make me a new variable called $currentUser and make it of the myUser
    // class type, and when making it, fetch me the details of student ID 6 and populate it
    // with their data.

    if($currentUser->checkUserLevel('math',3))
    // Now I am using one of the functions called checkUserLevel, supplying it
    // with the two arguments it needs and depending on it it returns true or false
    // doing one action or another.
    {
        echo "The user is at least level 3.
";
    }
    else
    {
        echo "The user is lower than level 3.
";
    }

    if($currentUser->checkUserLevel('biology',12))
    // same check, differnt inputs
    {
        echo "The user is at least level 3.
";
    }
    else
    {
        echo "The user is lower than level 3.
";
    }


    // You can output like this for example:
    echo "The users math is at: ".$currentUser->math;

    // and I added a little function that will simply return the level for you of the subject you enter.
    echo "The user is at math level ".$currentUser->returnUserLevel('math');

    // lastly you can do something like this:
    $allSubjects=array('math','physics','biology');
    for($i=0;$i<count($allSubjects);$i++)
    {
        echo "The users ".$allSubjects[$i]." level is at ".$currentUser->returnUserLevel($allSubjects[$i])."<br><br>";
    }

?>

The output of code is:

The user is at least level 3.

The user is lower than level 3.