I don't understand what does this code line do, $this->link->query($query)?

Question

Only the part which is $this->link->query($query) I understand that link is the member variable of the class Database but don't understand what is happening when $this->link->query($query) executes? help, I am a novice at coding

My whole code:

<?php


class Database
{
    public $db_host=DB_HOST;
    public $db_user=DB_USER;
    public $db_pass=DB_PASS;
    public $db_name=DB_NAME;


    public $link;

    public $error;

    public function __construct()

    {



        // Call connect function

        $this->connect();


    }

    private function connect()
    {
        $this->link= new mysqli($this->db_host,$this->db_user,$this->db_pass,$this->db_name);

        if(!$this->link)
        {
            $this->error="Connection Failed";
            return false;
        }

    }

    public function select($query)
    {
        $result=$this->link->query($query) or die ("Query could not execute");
    }

}


?>

I'm not grasping the question here. What's the "problem"? It works or it doesn't? Or, you want to know "how" it all comes together? — Funk Forty Niner, Jul 26 '16 at 15:29
problem is that I don't understand how "$this->link->query($query)" is working. I am accessing "$link" member variable using "$this->link" but don't understand what "$this->link->query($query)" is? — Pranav Raj, Jul 26 '16 at 15:31
you also realize that these `public $db_host=DB_HOST; public $db_user=DB_USER; public $db_pass=DB_PASS; public $db_name=DB_NAME;` at the end, are all constants. Where are those defined? — Funk Forty Niner, Jul 26 '16 at 15:32
yes, it works. but I want to know how it comes altogether. I was following a course video and intstructor wrote this without explaining much about it. — Pranav Raj, Jul 26 '16 at 15:32
It's all in the manual(s) http://php.net/manual/en/language.oop5.php --- http://php.net/manual/en/language.oop5.basic.php — Funk Forty Niner, Jul 26 '16 at 15:33
I would say that it is bad form to directly access a property of a class, as it ruins encapsulation.... — ArtisticPhoenix, Jul 26 '16 at 15:35
and Stack isn't a tutorial site. There's enough out there for you to learn. If nothing is "broke", then there's nothing for us to "fix". — Funk Forty Niner, Jul 26 '16 at 15:37

score 0 · Accepted Answer · edited Jul 26 '16 at 15:38

0

$this is the current Database object you are using.
-> calls a method or member of that object
link as you pointed out is a member of Database which just happens to be another object of mysqli.
query($query) is a method of link.

So you are calling mysqli query. Where the param $query should be your sql

edited Jul 26 '16 at 15:38

Nana Partykar

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answered Jul 26 '16 at 15:32

nerdlyist

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Thanks! Thanks a lot! I know Stack Overflow isn't tutorial site but you just cleared a major confusion. – Pranav Raj Jul 26 '16 at 15:48

score 0 · Answer 2 · answered Jul 26 '16 at 15:32

$this->link is a database connection object, and it has a method called query() for doing database queries and returning a mysqli result object. The query() method takes an SQL string. So one way to invoke it would be:

$result = $this->link->query("SELECT * FROM table WHERE 1") ;

It's very common to use a variable instead of a string literal in calls to mysqli query():

$sql = "SELECT * FROM table WHERE 1" ;
$result = $this->link->query($sql) ;

In the case of your code, the variable containing the SQL string is called $query, which can be kind of confusing, especially since $query isn't defined anywhere that I can see.

I don't understand what does this code line do, $this->link->query($query)?

2 Answers2