Query DB with a class

Question

I'm still playing around with classes and can't get this one running:

class db_connection {
    private $dbc;


    public function __construct()
    {
        $this->dbc = new mysqli(HOST_ONE, USER_ONE, PASS_ONE, DB_ONE);

    }

    public function getDbc()
    {
        return $this->dbc;
    }

}

class db_query extends db_connection{
    private $querystring;

    private $result;

    function __construct ($table, $field) {
        $this->querystring = $query = parent::getDbc()->query("SELECT ".$field." FROM ".$table);
        $this->result = $row = $query->fetch_assoc();
    }
    function get_resultset() {
        return $this->result;
    }
}

this is how I try to run it:

$db_conn = new db_connection();
$db = $db_conn->getDbc();

$action = new db_query('datenbanken','id');
$result = $action->get_resultset();
var_dump($result);

The connection is established without any problems, but it won't query the database with my class.

I won't to achieve that I can run a query and only have to set

$action = new db_query('datenbanken','id');

this line...

Can someone help me on how I can solve this? Thanks!

vertazzar · Accepted Answer · 2014-11-05 15:31:36Z

2

you need to call parent constructor when overriding the class you extend, so in this case

class db_query extends db_connection{
    private $querystring;

    private $result;

    function __construct ($table, $field) {
        parent::__construct(); // now we have $this->dbc constructed
        $this->querystring = $query = $this->getDbc()->query("SELECT ".$field." FROM ".$table);
        $this->result = $row = $query->fetch_assoc();
    }
    function get_resultset() {
        return $this->result;
    }
}

note that parent keyword is only used if you want to call the function from the class that you extend

in your case $this gets populated, so there is no need to use parent::getDbc(), instead you should use $this->getDbc()

however if you were overriding getDbc you would have:

class my_other_class extends db_connection{

    function getDbc() {
        // call parent funct
        $res = parent::getDbc();
        $res = doSomethingWithRes($res);
        return $res;
    }
}

answered Nov 5, 2014 at 15:31

vertazzar

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3 Comments

Steve Over a year ago

Might as well remove the unused $query and $row variables as well

baao Over a year ago

Excellent, that works for one row. Thank you! Shall I do the while loop inside the class or when running the class?

vertazzar Over a year ago

i leave the design of your database driver to your imagination, however if i were you i would look into some most popular ORMs such as en.wikipedia.org/wiki/Doctrine_(PHP) and for something simpler you can look into github to find some lightweight open source library from which you can learn / improve

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