How do I convert a script using mysql_ functions to use mysqli_ functions?

Question

EDIT: Whether or not to use mysqli_ is outside the scope of this question. Consider using PDO.

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What steps need to be taken to convert a script from using the deprecated mysql_ functions to mysqli_?

Is there anything that needs to be done differently when using mysqli_ instead of mysql?

Here's a basic script using mysql_ functions:

<?php

//define host, username and password

$con = mysql_connect($host,$username,$password);
if (!$con) {
    die('Could not connect: ' . mysql_error());
}

$db_name ="db1";
mysql_select_db($dbname, $con);

$value1 = mysql_real_escape_string($input_string);

$query = 'SELECT * FROM table1 WHERE table1.col1=' . $value1 . '';
$result = mysql_query($query, $con);

while($row = mysql_fetch_assoc*$result)
{
    $col1 = $row['col1'];
    $col2 = $row['col2'];

    echo $col1 . ' ' . $col2 . '<br />';
}

mysql_close($con);
?>

Answer 1

Note: Converting from mysql_ to mysqli_ may not be optimal. Consider PDO if you're prepared to convert all of your code to OOP.

It can be tempting to try to replace all instances of mysql_ with mysqli_ and pray it works. You'd be close but not quite on point.

Connecting to the database:

Fortunately, mysqli_connect works closely enough to mysql_query that you can just swap out their function names.

mysql_:

$con = mysql_connect($host, $username, $password);

mysqli_:

$con = mysqli_connect($host, $username, $password);

Selecting a database

Now, with most of the other functions in the mysqli_ library, you'll need to pass mysqli_select_db the database connection as its first parameter. Most of the mysqli_ functions require the connection object first.

For this function, you can just switch the order of the arguments you pass to the function. If you didn't pass it a connection object before, you have to add it as the first parameter now.

mysql_:

mysql_select_db($dbname, $con);

mysqli_:

mysqli_select_db($con, $dbname);

As a bonus, you can also pass the database name as the fourth parameter to mysqli_connect - bypassing the need to call mysqli_select_db.

$con = mysqli_connect($host, $username, $password, $dbname);

Sanitize user input

Using mysqli_real_escape_string is very similar to mysql_real_escape_string. You just need to pass the connection object as the first parameter.

mysql_:

$value1 = mysql_real_escape_string($input_string);

mysqli_:

$value1 = mysqli_real_escape_string($con, $input_string);

Very Important: Preparing and Running a Query

One reason the mysql_ functions were deprecated to begin with was their inability to handle prepared statements. If you simply convert your code to mysqli_ without taking this important step, you are subject to some of the largest weaknesses of the mysql_ functions.

It's worth reading these articles on prepared statements and their benefits:

Wikipedia - Prepared Statements

PHP.net - MySQLi Prepared Statements

Note: When using prepared statements, it's best to explicitly list each column you're attempting to query, rather than using the * notation to query all columns. This way you can ensure you've accounted for all of the columns in your call to mysqli_stmt_bind_result.

mysql_:

$query = 'SELECT * FROM table1 WHERE table1.col1=' . $value1 . '';
$result = mysql_query($query, $con);
while($row = mysql_fetch_assoc*$result)
{
    $col1 = $row['col1'];
    $col2 = $row['col2'];

    echo $col1 . ' ' . $col2 . '<br />';
}

mysqli_:

$query = 'SELECT col1,col2 FROM table1 WHERE table1.col1=?';
if ($stmt = mysqli_prepare($link, $query)) {

    /* pass parameters to query */
    mysqli_stmt_bind_param($stmt, "s", $value1);

    /* run the query on the database */
    mysqli_stmt_execute($stmt);

    /* assign variable for each column to store results in */
    mysqli_stmt_bind_result($stmt, $col1, $col2);

    /* fetch values */
    while (mysqli_stmt_fetch($stmt)) {
        /*
            on each fetch, the values for each column 
            in the results are automatically stored in 
            the variables we assigned using 
            "mysqli_stmt_bind_result"
        */
        echo $col1 . ' ' . $col2 . '<br />';
    }

    /* close statement */
    mysqli_stmt_close($stmt);
}

Showing errors

Showing errors works a little differently with mysqli_. mysqli_error requires the connection object as its first parameter. But what if the connection failed? mysqli_ introduces a small set of functions that don't require the connection object: the mysqli_connect_* functions.

mysql_:

if (!$con) {
    die('Could not connect: ' . mysql_error());
}

if (!$result) {
    die('SQL Error: ' . mysql_error());
}

mysqli_:

/* check connection error*/
if (mysqli_connect_errno()) {
    die( 'Could not connect: ' . mysqli_connect_error() );
}

/* check query error */
if ($stmt = mysqli_prepare($link, $query)) {

    // ... execute query

    if (mysqli_stmt_error($stmt)) {
        echo 'SQL Error: ' . mysqli_stmt_error($stmt);
    }
}

Answer 2

EXAMPLE.

This is your dbc class

<?php

class dbc {

    public $dbserver = 'server';
    public $dbusername = 'user';
    public $dbpassword = 'pass';
    public $dbname = 'db';

    function openDb() {    
        try {
            $db = new PDO('mysql:host=' . $this->dbserver . ';dbname=' . $this->dbname . ';charset=utf8', '' . $this->dbusername . '', '' . $this->dbpassword . '');
        } catch (PDOException $e) {
            die("error, please try again");
        }        
        return $db;
    }

    function getAllData($qty) {
        //prepared query to prevent SQL injections
        $query = "select * from TABLE where qty = ?";
        $stmt = $this->openDb()->prepare($query);
        $stmt->bindValue(1, $qty, PDO::PARAM_INT);
        $stmt->execute();
        $rows = $stmt->fetchAll(PDO::FETCH_ASSOC);
        return $rows;
    }    
?>

your PHP page:

<?php 
require "dbc.php";

$getList = $db->getAllData(25);

foreach ($getList as $key=> $row) {
         echo $row['columnName'] .' key: '. $key;
    }