OOP database connect/disconnect class

Question

I have just started learning the concept of Object oriented programming and have put together a class for connecting to a database, selecting database and closing the databa

Answer 1

<?php

class Database{

    private $link;
    //private $host,$username,$password,$database;
    //private $status;

    public function __construct(){

        $this->host         =   'localhost';
        $this->username     =   'root';
        $this->password     =   '';
        $this->database     =   'workclass';

        $this->link = mysqli_connect($this->host,$this->username,$this->password);

        $this->status = mysqli_select_db($this->link,$this->database);

        if (!$this->status) {
            return $this->status="Failed to Connected with Database";
        }else{
            return $this->status="Database is connected";
        }
    }
}

$object = new Database();

echo $object->status;

?>

Answer 2

Object Oriented Programming works well with PDO and mysqli. Give it a try

Answer 3

I would add a connection/link variable to your class, and use a destructor. That will also save you from haveing to remember to close your connection, cause it's done automatically.
It is the $this->link that you need to pass to your mysql_close().

class Database {

    private $link;
    private $host, $username, $password, $database;

    public function __construct($host, $username, $password, $database){
        $this->host        = $host;
        $this->username    = $username;
        $this->password    = $password;
        $this->database    = $database;

        $this->link = mysql_connect($this->host, $this->username, $this->password)
            OR die("There was a problem connecting to the database.");

        mysql_select_db($this->database, $this->link)
            OR die("There was a problem selecting the database.");

        return true;
    }

    public function query($query) {
        $result = mysql_query($query);
        if (!$result) die('Invalid query: ' . mysql_error());
        return $result;
    }

    public function __destruct() {
        mysql_close($this->link)
            OR die("There was a problem disconnecting from the database.");
    }

}

Example Usage:

<?php
    $db = new Database("localhost", "username", "password", "testDatabase");

    $result = $db->query("SELECT * FROM students");

    while ($row = mysql_fetch_assoc($result)) {
        echo "First Name: " . $row['firstname'] ."<br />";
        echo "Last Name: "  . $row['lastname']  ."<br />";
        echo "Address: "    . $row['address']   ."<br />";
        echo "Age: "        . $row['age']       ."<br />";
        echo "<hr />";
    }
?>

Edit:
So people can actually use the class, I added the missing properties/methods.
The next step would be to expand on the query method, to include protection against injection, and any other helper functions.
I made the following changes:

• Added the missing private properties
• Added __construct($host, $username, $password, $database)
• Merged connectdb() and select() into __construct() saving an extra two lines of code.
• Added query($query)
• Example Usage

Please if I made a typo or mistake, leave a constructive comment, so I can fix it for others.

edit 23/06/2018

As pointed out mysql is quite outdated and as this question still receives regular visits I thought I'd post an updated solution.

class Database {

    private $mysqli;
    private $host, $username, $password, $database;

    /**
     * Creates the mysql connection.
     * Kills the script on connection or database errors.
     * 
     * @param string $host
     * @param string $username
     * @param string $password
     * @param string $database
     * @return boolean
     */
    public function __construct($host, $username, $password, $database){
        $this->host        = $host;
        $this->username    = $username;
        $this->password    = $password;
        $this->database    = $database;

        $this->mysqli = new mysqli($this->host, $this->username, $this->password)
            OR die("There was a problem connecting to the database.");

        /* check connection */
        if (mysqli_connect_errno()) {
            printf("Connect failed: %s\n", mysqli_connect_error());
            exit();
        }

        $this->mysqli->select_db($this->database);

        if (mysqli_connect_errno()) {
            printf("Connect failed: %s\n", mysqli_connect_error());
            exit();
        }

        return true;
    }

    /**
     * Prints the currently selected database.
     */
    public function print_database_name()
    {
        /* return name of current default database */
        if ($result = $this->mysqli->query("SELECT DATABASE()")) {
            $row = $result->fetch_row();
            printf("Selected database is %s.\n", $row[0]);
            $result->close();
        }
    }

    /**
     * On error returns an array with the error code.
     * On success returns an array with multiple mysql data.
     * 
     * @param string $query
     * @return array
     */
    public function query($query) {
        /* array returned, includes a success boolean */
        $return = array();

        if(!$result = $this->mysqli->query($query))
        {
            $return['success'] = false;
            $return['error'] = $this->mysqli->error;

            return $return;
        }

        $return['success'] = true;
        $return['affected_rows'] = $this->mysqli->affected_rows;
        $return['insert_id'] = $this->mysqli->insert_id;

        if(0 == $this->mysqli->insert_id)
        {
            $return['count'] = $result->num_rows;
            $return['rows'] = array();
            /* fetch associative array */
            while ($row = $result->fetch_assoc()) {
                $return['rows'][] = $row;
            }

            /* free result set */
            $result->close();
        }

        return $return;
    }

    /**
     * Automatically closes the mysql connection
     * at the end of the program.
     */
    public function __destruct() {
        $this->mysqli->close()
            OR die("There was a problem disconnecting from the database.");
    }
}

Example usage:

<?php
    $db = new Database("localhost", "username", "password", "testDatabase");

    $result = $db->query("SELECT * FROM students");

    if(true == $result['success'])
    {
        echo "Number of rows: " . $result['count'] ."<br />";
        foreach($result['rows'] as $row)
        {
            echo "First Name: " . $row['firstname'] ."<br />";
            echo "Last Name: "  . $row['lastname']  ."<br />";
            echo "Address: "    . $row['address']   ."<br />";
            echo "Age: "        . $row['age']       ."<br />";
            echo "<hr />";
        }
    }

    if(false == $result['success'])
    {
        echo "An error has occurred: " . $result['error'] ."<br />";
    }
?>

Answer 4

mysql_close requires a parameter to disconnect but you are providing nothing.

class Database {

    private $host, $username, $password, $con;

    public function __construct($ihost, $iusername, $ipassword){
        $this->host = $ihost;
        $this->username = $iusername;
        $this->password = $ipassword;
        $this->con = false;
    }


    public function connect() {
        $connect = mysql_connect($this->host, $this->username, $this->password);
        return $connect;
    }


    public function connectdb(){
        $conn = $this->connect();
        if($conn)
        {
            $this->con = true;
            echo "Successsfully Connected. 
";
            return true;
        }
        else {
            echo "Sorry Could Not Connect. 
";
            return false;
        }
    }


    public function select($database){
        if($this->con)
        {
            if(mysql_select_db($database))
            {
                echo "Successfully Connected Database. $database. 
";
                return true;
            }
            else
            {
                echo "Unknown database. 
";
            }
        }
        else {
            echo "No active Connection. 
";
            return false;
        }
    }


    public function disconnectdb(){
        if($this->con)
        {
            if(mysql_close($this->connect()))
            {
                $this->con = false;
                echo "Successfully disconnected. 
";
                return true;
            }
        }
        else
        {
            echo "Could Not disconnect. 
";
            return false;
        }
    }

}

    $database = new database('localhost', 'root', '');
    $database->connectdb();
    $database->select('databaseoffacebook');
    $database->disconnectdb();

Answer 5

You should be aware that mysql_* functions were introduced in PHP 4, which is more then 1 yours ago. This API is extremely old, and the process has begun to actually deprecating this extension.

You should not in 2012 write new code with mysql_* functions.

There exist two very good alternative : PDO and MySQLi. Both of which are already written with object oriented code in mind, and they also give you ability to use prepared statements.

That example you showed in the original post written with PDO would look like this:

//connect to the the database
$connection = new PDO('mysql:host=localhost;dbname=msm', 'username', 'password');
//disconnects
$connection = null;

Of course there are more complicated use-case, but the point stand - time to evolve.

Answer 6

you're not returning anything from connectdb() yet you're passing this function's return to mysql_close().