Connect to DB and Activites by OOP in PHP - php

Question

Hi I am having some issues connecting to my DB using OO PHP. My script is below. I have been going at this for a while now. This is just a test script as I am fairly new to OOP. Please don't be harsh
class Database{
public $mysqli,
$host,
$username,
$password,
$db;
public function __construct($host, $username, $password, $db){
$this->host = $host;
$this->username = $username;
$this->password = $password;
$this->db = $db;
$mysqli = new mysqli($host, $username, $password, $db);
if (!$mysqli){
echo "error in connecting to database";
}
else{
echo "success in connecting to database";
}
}
public function query(){
$result = $mysqli->query("SELECT * FROM inventory");
if ($result) {
printf("Select returned %d rows.\n", $result->num_rows);
$result->close();
}
else{
echo "there is an error in query";
$result->close();
}
//echo "in query function";
}
}
Usage...
$DB = new Database('localhost', 'root', 'xxxx', 'yyyy');
$DB -> query();

Answer 1

Your main problem is that you aren't storing a value into your class' $mysqli property. You need to use $this->mysqli in your constructor and query method instead of $mysqli.
Secondly, this class adds nothing that the mysqli class doesn't already have. You might as well simply use
$DB = new mysqli('localhost', 'root', 'xxxx', 'yyyy');
if ($DB->connect_error) {
throw new Exception($DB->connect_error, $DB->connect_errno);
}

Answer 2

The problem is, you are accessing the class property without $this. The $mysqli should be in $this->mysqli in constructor function.
You are using mysqli property as Object of mysqli class.
Then you can use the query function of mysqli property object(In Database class) by $this->mysqli->query("SELECT * FROM inventory") in query function.
Updated Code:
<?php
class Database{
public $mysqli,
$host,
$username,
$password,
$db;
public function __construct($host, $username, $password, $db){
$this->host = $host;
$this->username = $username;
$this->password = $password;
$this->db = $db;
$this->mysqli = new mysqli($host, $username, $password, $db);
/* check connection */
if ($this->mysqli->connect_errno) {
printf("Connect failed: %s\n", $this->mysqli->connect_error);
exit();
} else {
echo "success in connecting to database";
}
}
public function query(){
$result = $this->mysqli->query("SELECT * FROM inventory");
if ($result) {
printf("Select returned %d rows.\n", $result->num_rows);
$result->close();
}
else{
echo "there is an error in query";
$result->close();
}
//echo "in query function";
}
}
$DB = new Database('localhost', 'root', 'xxxx', 'yyyy');
$DB -> query();

Answer 3

Try this:
$connection = mysqli_connect(DB_SERVER, DB_USER, DB_PASS, DB_NAME);
// Test if connection succeeded
if(mysqli_connect_error()){
die("Database connection failed: " .
mysqli_connect_error() .
" (" . mysqli_connect_errno() . ")"
);
}