function __construct

[mactron]

Hi! I'm new here 

I'm following an online course where we building CMS using OOP PHP and PDO. I read some articles and watched a few youtube tutorials and to be honest, I'm pretty confused. Some of the developers suggest using function __construct(PDO $connection) inside the class.

Their code looks something like that:

  private PDO $connection;
  function __construct(PDO $connection) {
    $this->connection = $connection;

connect.php

class dbh{
    
        private $host = "localhost";
        private $user = "root";
        private $pwd = "";
        private $dbname = "cms";

        protected function connect() {
            $dsn = 'mysql:host=' . $this->host . ';dbname=' . $this->dbname;
            $pdo = new PDO ($dsn, $this->user, $this->pwd);
            $pdo->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);
            return $pdo;

    }
}

function.php // not a whole code
 

class CategoriesData extends dbh{

    public function getAllCategories() {

			$sql = "SELECT * FROM categories_tbl";
			$stmt = $this->connect()->query($sql);
				while ($row = $stmt->fetch()){
				
				echo $row['category_name'] . '<br>';

		}
    }

 	public function getCategoryName() {

			$sql = "SELECT category_name FROM categories_tbl";
			$stmt = $this->connect()->prepare($sql);
			$stmt->execute();
			$category = $stmt->fetch(PDO::FETCH_OBJ);
			
			if($category == null) {

				return null;
			}else {

				return $category->category_name;
			}
    } 

	public function getCategoryDetials() {

			$sql = "SELECT * FROM categories_tbl";
			$stmt = $this->connect()->prepare($sql);
			$stmt->execute();
			$result = $stmt->fetchAll((PDO::FETCH_OBJ));
			
			return $result;
    }   
		
    public function addCategory ($filter_name, $filter_title, $filter_description, $filter_slug) {

			$sql = "INSERT INTO categories_tbl (category_name, category_title, category_description, category_slug) VALUES (?, ?, ?, ?)";
			$stmt = $this->connect()->prepare($sql);
			$stmt->execute([$filter_name, $filter_title, $filter_description, $filter_slug]);
 
		}

	public function deleteCategory($delete_category_id) {
			$sql =  "DELETE FROM categories_tbl WHERE category_id = ?";
			$stmt = $this->connect()->prepare($sql);
			$stmt->execute([$delete_category_id]);
    }
    }
       }
   

 

[Barand]

Do not create a connection every time you want to execute a query.

1. connecting probably takes longer than the query so you more than double the execution time
2. you will soon run out of connections
3. certain functions (such as lastInsert() ) are valid only in the current connection

Create the connection (once per script unless more than one server is used), store in $this->connection, or similar,  and use that each time for the function calls.

[mactron]

Honestly speaking I don't know how to use this function inside my class. Did I miss something? Is my code above completely wrong? Please note: The code works like a charm I just don't understand the concept of using function __construct(PDO $connection). Any advice is appreciated! Thanks!

Edited February 14, 2020 by mactron

[ginerjm]

Have you done any reading on how classes work and how they act when first opened?  When one makes a call such as

"$myclass_hdl = new MYClass()"

one does an "instantiation" of that class and assigns a handle that you continue to use to make further calls to that class and its methods and values.  What happens with that "new" call is the construction of a class instance.  Whatever you need to do to establish one occurrence (instance) of your class happens at this time.

Reading the manual might improve your understanding.

[mactron]

Hi,

is this correct way? I'm on the right path? Thanks!

class PostsData extends dbh{


    private $conn;

    public function __construct() {
    $this->conn = new dbh();
    $this->conn = $this->conn->connect();

}

    public function getPosts() {

            $sql = "SELECT * FROM posts_tbl";
            $stmt = $this->connect()->prepare($sql);
            $stmt->execute();
            $result = $stmt->fetchAll((PDO::FETCH_OBJ));

            return $result;
            
    }

    public function addPost($filter_author, $filter_title, $filter_txt) {

            $sql = "INSERT INTO posts_tbl (post_author, post_title, post_txt) VALUES (?, ?, ?, ?)";
            $stmt = $this->connect()->prepare($sql);
            $stmt->execute([$filter_author, $filter_title, $filter_txt]);

        }

    }

$post = new PostsData();
$posts = $post->getPosts();

foreach ($posts as $post) { 

echo $post->post_title;

}

 

[Barand]

You are still connecting in each of your functions instead of just once.

Try

<?php


class dbh{
    
        private $host = "localhost";
        private $user = "root";
        private $pwd = "";
        private $dbname = "cms";
        protected $conn;                               // make available to subclass
        
        public function __construct()
        {
            $this->conn = $this->connect();
        }
        
        
        private function connect() {
            $dsn = 'mysql:host=' . $this->host . ';dbname=' . $this->dbname;
            $pdo = new PDO ($dsn, $this->user, $this->pwd);
            $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
            $pdo->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);
            $pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
            return $pdo;

    }
}



class PostsData extends dbh{

    public function getPosts() {

            $sql = "SELECT * FROM posts_tbl";
            $stmt = $this->conn->prepare($sql);
            $stmt->execute();
            $result = $stmt->fetchAll((PDO::FETCH_OBJ));

            return $result;
            
    }

    public function addPost($filter_author, $filter_title, $filter_txt) {

            $sql = "INSERT INTO posts_tbl (post_author, post_title, post_txt) VALUES (?, ?, ?)";
            $stmt = $this->conn->prepare($sql);
            $stmt->execute([$filter_author, $filter_title, $filter_txt]);

    }

}


$post = new PostsData();
$posts = $post->getPosts();

foreach ($posts as $post) { 
    echo $post->post_title . '<br>';
}
     
?>

 

[mactron]

Your code works, but I don't have a clue with how many connections. Thanks!

[Barand]

Your method creates a connection each time you run a query.

That method creates a single connection for each object and uses it for all the queries in the object.

Better still would be to create a single connection for the page and pass that one connection to each new object when it is created.

At the top of each page, have

require 'db_inc.php';            // <--- CONTAINS -----  #  const HOST = "localhost";
                                                         #  const USER = "root";
                                                         #  const PWD  = "";
                                                         #  const DBNAME = "cms";
                                                         #
                                                         #  function pdoconnect()
                                                         #  {
                                                         #     $dsn = 'mysql:host=' . HOST . ';dbname=' . DBNAME;
                                                         #     $pdo = new PDO ($dsn, USER, PWD);
                                                         #     $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
                                                         #     $pdo->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);
                                                         #     $pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
                                                         #     return $pdo;
                                                         #   }
                                                         #
                                                                                             
        
$connection = pdoconnect();                            // create connection

then your code becomes

<?php

class dbh {   
        protected $conn;
        
        public function __construct($connection) 
        {
            $this->conn = $connection;
        }

}        
        
        
class PostsData extends dbh{

    public function getPosts() {

            $sql = "SELECT * FROM posts_tbl";
            $stmt = $this->conn->prepare($sql);
            $stmt->execute();
            $result = $stmt->fetchAll((PDO::FETCH_OBJ));

            return $result;
            
    }

    public function addPost($filter_author, $filter_title, $filter_txt) {

            $sql = "INSERT INTO posts_tbl (post_author, post_title, post_txt) VALUES (?, ?, ?)";
            $stmt = $this->conn->prepare($sql);
            $stmt->execute([$filter_author, $filter_title, $filter_txt]);

    }

}


$post = new PostsData($connection);               // pass connection to new object

$posts = $post->getPosts();

foreach ($posts as $post) { 
    echo $post->post_title . '<br>';
}
     
?>

 

Edited February 15, 2020 by Barand