Why function __construct is not working in PHP? - php

Question

Can someone explain
Why this did not works ?
<?php
class category
{
function __construct()
{
$con = new mysqli("localhost", "root", "", "whatever");
}
function show_all()
{
$sql = "SELECT id_kategori, nama_kategori FROM kategori";
$stmt = $con->prepare($sql);
$stmt->execute();
$stmt->bind_result($id, $cat);
while($stmt->fetch())
{
echo "<td>$id</td>";
echo "<td>$cat</td>";
echo "<td>Update</td>";
echo "<td>Delete</td>";
};
$stmt->close();
}
}
?>
But this works ?
<?php
class category
{
function show_all()
{
$con = new mysqli("localhost", "root", "", "whatever");
$sql = "SELECT id_kategori, nama_kategori FROM kategori";
$stmt = $con->prepare($sql);
$stmt->execute();
$stmt->bind_result($id, $cat);
while($stmt->fetch())
{
echo "<td>$id</td>";
echo "<td>$cat</td>";
echo "<td>Update</td>";
echo "<td>Delete</td>";
};
$stmt->close();
}
}
?>
Without construct, it works, with construct it's don't.
Can somebody show me, tell me, teach me how to include sql connection in a construct the right way ? I'm still new and learning by the way.

Answer 1

This is because of scoping. The $con variable should be defined to be used in the class exclusively rather than just locally inside the __construct.
When you define $con inside the __construct you are scoping this to be locally used inside the function __construct rather than in the class itself
Consider the following code
<?php
class category
{
private $con;
function __construct()
{
$this->con = new mysqli("localhost", "root", "", "whatever");
}
function show_all()
{
$sql = "SELECT id_kategori, nama_kategori FROM kategori";
$stmt = $this->con->prepare($sql);
$stmt->execute();
$stmt->bind_result($id, $cat);
while($stmt->fetch())
{
echo "<td>$id</td>";
echo "<td>$cat</td>";
echo "<td>Update</td>";
echo "<td>Delete</td>";
};
$stmt->close();
}
}
?>

Answer 2

$con is not a variable accessible in the class above: Try this:
<?php
class category
{
private $con = NULL;
function __construct()
{
$this->con = new mysqli("localhost", "root", "", "whatever");
}
function show_all()
{
$sql = "SELECT id_kategori, nama_kategori FROM kategori";
$stmt = $this->con->prepare($sql);
$stmt->execute();
$stmt->bind_result($id, $cat);
while($stmt->fetch())
{
echo "<td>$id</td>";
echo "<td>$cat</td>";
echo "<td>Update</td>";
echo "<td>Delete</td>";
};
$stmt->close();
}
}
?>
and look at documentation here:
http://php.net/manual/en/language.oop5.php
and look up php scope:
http://php.net/manual/en/language.variables.scope.php
Also if you are having questions always add this to your code:
This would have told you the variable is undefined:
error_reporting(E_ALL);
ini_set('display_errors', '1');