PHP OOP query() error - Call to undefined method connection::query() - php

Question

Im trying to insert data into mysql database.
I have class connection
class connection{
function __construct(){
$servername = 'localhost';
$username = 'root';
$password = '';
$database='products2';
// Create connection
$conn = new mysqli($servername, $username, $password,$database);
// Check connection
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
return false;
}else{
echo "succesful connection!</br>";
$this->query=$conn;
return true;
}
}
}
And another class in witch I try to insert data into database(i try to do this in __construct of that class)
$sql="INSERT INTO products (name,price,category,f_material,f_size) VALUES ('nosaukums','cena','kategorija,'materials','izmers')";
$db=new connection();
$result=$db->query($sql);
However I get this errror:
Fatal error: Call to undefined method connection::query() in ....

Answer 1

In order to use the query (from mysqli class) method you need to create a new method public function query() {}. This method will be able to use the mysqli method. In the end, you will be able to acheive the same result but by applying 'query' on your own object ($db) like so $result = $db->query($sql);
Here's the class :
<?php
class connection{
// define a variable for the database connection
private $conn;
// when an instance of 'connection' class is created a connection is made through mysqli
public function __construct()
{
$servername = 'localhost';
$username = 'root';
$password = '';
$database='products2';
// the connection is stored inside the private variable
$this->conn = new mysqli($servername, $username, $password,$database);
// Check connection
if ($this->conn->connect_error) {
die("Connection failed: " . $this->conn->connect_error);
return false;
} else{
echo "succesful connection!</br>";
return true;
}
}
// method used to send a query to database
public function query($sql)
{
// here you use the connection made on __construct() and apply the method query. Basically we are using inside our method (called query) a method (call query too) from the mysqli class
$this->conn->query($sql);
return true;
}
}
Calling the method :
<?php
// prepare the SQL request
$sql = "INSERT INTO products (name,price,category,f_material,f_size) VALUES ('nosaukums','cena','kategorija,'materials','izmers')";
// create a new instance of the class connection
$db = new connection();
// run the method $sql on the newly created instance $db
$result = $db->query($sql);

Answer 2

Because in your last line - $result = $db->query($sql); - you are trying to call a function named 'query'. If you look inside your connection class the only function you have is the constructor.
To fix this you are going to need to add a function called "query" (note this is not an ideal name for the function).
Here is some commented code (not guaranteed to be error free!)
class connection{
protected $conn; // add conn so that you can use it later
function __construct()
{
$servername = 'localhost';
$username = 'root';
$password = '';
$database='_mvc';
// Assign $this->conn to a database object
$this->conn = new mysqli($servername, $username, $password, $database);
// Remember we are checking >>THIS<< conn now
if ($this->conn->connect_error) {
die("Connection failed: " . $this->conn->connect_error);
return false;
}else{
// no need to assign anthing here as the database object has already been assigned to $this->conn
echo "succesful connection!</br>";
return true;
}
}
// here is the missing function
public function query($sql) {
// now we are accessing the database objects query method and massing the SQL
return $this->conn->query($sql);
}
}
$sql =
"INSERT INTO products (name,price,category,f_material,f_size)
VALUES ('nosaukums','cena','kategorija,'materials','izmers')";
$db = new connection();
$result = $db->query($sql);
I would recommend you jump straight into php data objects and be done with it because PDO is the best 'standard' way to access databases these days.