What arguments should be passed to PDO::__construct()? - php

Question

I'm a new in web programming and would ask the advice for code below.
I have the code in class Database. There is it. As you see there's a connect to database with mysqli. And this code work.
function __construct() {
$this->conn = $this->connectDB();
}
function connectDB() {
$conn = mysqli_connect($this->host,$this->user,$this->password,$this->database);
return $conn;
}
function runBaseQuery($query) {
$result = mysqli_query($this->conn,$query);
while($row=mysqli_fetch_assoc($result)) {
$resultset[] = $row;
}
if(!empty($resultset))
return $resultset;
}
function runQuery($query, $param_type, $param_value_array) {
$sql = $this->conn->prepare($query);
$this->bindQueryParams($sql, $param_type, $param_value_array);
$sql->execute();
$result = $sql->get_result();
if ($result->num_rows > 0) {
while($row = $result->fetch_assoc()) {
$resultset[] = $row;
}
}
if(!empty($resultset)) {
return $resultset;
}
}
function bindQueryParams($sql, $param_type, $param_value_array) {
$param_value_reference[] = & $param_type;
for($i=0; $i<count($param_value_array); $i++) {
$param_value_reference[] = & $param_value_array[$i];
}
call_user_func_array(array(
$sql,
'bind_param'
), $param_value_reference);
}
function insert($query, $param_type, $param_value_array) {
$sql = $this->conn->prepare($query);
$this->bindQueryParams($sql, $param_type, $param_value_array);
$sql->execute();
}
function update($query, $param_type, $param_value_array) {
$sql = $this->conn->prepare($query);
$this->bindQueryParams($sql, $param_type, $param_value_array);
$sql->execute();
}
I have to write this class in PDO. I've done it, but something is wrong. I try to connect my Database and get the error
Fatal error: Uncaught TypeError: PDO::__construct() expects parameter 4
class DB {
private $host = "";
private $user = "";
private $password = "";
private $database = "";
private $pdo;
function __construct() {
$this->pdo = $this->connectDB();
}
function connectDB() {
try
{
$pdo = new PDO($this->host,$this->user,$this->password,$this->database);
}
catch (PDOException $e) {
print "Error!: " . $e->getMessage();
}
die();
}
function runBaseQuery($query)
{
$result = $pdo->query($query);
while ($row = $pdo->fetch(PDO::FETCH_ASSOC)) {
$resultset[] = $row;
}
if (!empty($resultset))
return $resultset;
}
function runQuery($query, $param_type, $param_value_array) {
$sql = $pdo->prepare($query);
$pdo->execute($sql, $param_type, $param_value_array);
$result = $pdo->fetchAll(PDO::FETCH_ASSOC);
if ($result->num_rows > 0) {
while ($row = $pdo->fetchAll(PDO::FETCH_ASSOC)) {
$resultset[] = $row;
}
}
if(!empty($resultset)) {
return $resultset;
}
}
function bindQueryParams($sql, $param_type, $param_value_array) {
$param_value_reference[] = & $param_type;
for($i=0; $i<count($param_value_array); $i++) {
$param_value_reference[] = & $param_value_array[$i];
}
call_user_func_array(array(
$sql,
'bind_param'
), $param_value_reference);
}
function insert($query, $param_type, $param_value_array) {
$sql = $pdo->prepare($query);
$pdo->execute($sql, $param_type, $param_value_array);
}
function update($query, $param_type, $param_value_array) {
$sql = $pdo->prepare($query);
$pdo->execute($sql, $param_type, $param_value_array);
}
}
But my the new code don't work. Where is the problem?

Answer 1

Your new class has multiple problems. The one you are asking about can be solved by understanding how to connect properly with PDO and what DSN is. For this I have to refer you to this awesome article https://phpdelusions.net/pdo#dsn
Take this DSN for example:
mysql:host=localhost;dbname=test;port=3306;charset=utf8mb4
driver^ ^ colon ^param=value pair ^semicolon
You start by specifying which DB driver you would like to use: mysql:. After this comes a list of key-value pairs separated by a semicolon. The order should be host, DB name, and charset. You should specify all of these values.
Your DSN is your first argument to PDO::__construct(), the second and third is username and password respectively. The third one is an array of options.
Your options array should contain at least two values. You need to enable error reporting and switch off emulated prepared statements. These are the recommended settings.
Your connection should look at least similar to this:
$options = [
\PDO::ATTR_ERRMODE => \PDO::ERRMODE_EXCEPTION,
\PDO::ATTR_EMULATE_PREPARES => false,
];
$this->pdo = new PDO('mysql:host='.$this->host.';dbname='.$this->database.';charset=utf8mb4', $this->user, $this->password, $options);
However, please take note, that the constructor will be called once, and you do not need to put these values in private properties. They can simply be constants or hardcoded in the constructor. You will never need to reuse this values after opening connection.
Your second main mistake is that you are referring in a lot of places to $pdo, but you should be using $this->pdo.
Other notes:
die(); is going to end your whole script. Do not use it.
Do not catch exceptions, just to print out the error message. It defeats the whole purpose of the exceptions.
The method bindQueryParams() seems completely unnecessary. I would recommend you remove it.
runQuery is riddled with mistakes. $pdo->execute() takes in only one argument, which should be the array of values to be bound. There is no need for param type like in mysqli. The while loop is redundant and incorrect.
num_rows does not exist in PDO, and is not needed at all.
None of these method provide any benefit over just plain PDO.
Conclusion:
The class you have written is completely unnecessary and only makes your code more difficult to understand and maintain. While it might have made more sense with mysqli, PDO is simpler to use and does not need to be wrapped in such class. Please read the article linked at the beginning carefully, it will help you a lot.

Answer 2

The PDO connection does not take a 4th parameter for the database name. The DB name is passed in with the host name. So change:
$pdo = new PDO($this->host,$this->user,$this->password,$this->database);
to:
$pdo = new PDO($this->host . ';dbname=' . $this->database, $this->user, $this->password);
For more information see https://www.php.net/manual/en/pdo.connections.php
Additionally, it is unclear what $this->host contains but for PDO if that is just a host path you need to pass in the driver you are using as well, so you might even need to add
mysql:host=
to the start of this. With mysqli this is not required because the only RDBMS mysqli supports is mysql.
So potentially complete answer:
$pdo = new PDO('mysql:host=' . $this->host . ';dbname=' . $this->database, $this->user, $this->password);