Cannot query database in custom_helper?

[eluser]java[/eluser]
I have a function placed in custom_helper file :

Code:

function getCityName($id)
{
    $query = $this->db->getwhere('thanhpho', array('ThanhPhoID' => $id));
    $row = $query->row();
    return $row->Ten;
}

i want it automatically called in my view. But the view generated error:

Fatal error: Call to a member function on a non-object in d:\www\hoahau\system\application\helpers\custom_helper.php on line 181

and line 181 is my query command in function above.
What's the wrong in my code? Please tell.
Thanks for any response

[eluser]marcoss[/eluser]
[quote author="java" date="1183211431"]I have a function placed in custom_helper file :

Code:

function getCityName($id)
{
    $query = $this->db->getwhere('thanhpho', array('ThanhPhoID' => $id));
    $row = $query->row();
    return $row->Ten;
}

i want it automatically called in my view. But the view generated error:

Fatal error: Call to a member function on a non-object in d:\www\hoahau\system\application\helpers\custom_helper.php on line 181

and line 181 is my query command in function above.
What's the wrong in my code? Please tell.
Thanks for any response[/quote]

You have to instantiate CI if you want to use it out the flow, so you should go as follows,

Code:

$CI =& get_instance();
    
    function getCityName($id){
        $query = $CI->db->getwhere('thanhpho', array('ThanhPhoID' => $id));
        $row = $query->row();
        return $row->Ten;
    }

[eluser]java[/eluser]
I tried to instantiate CI but it still generate an error. I dont know it's not understand my query command.

[eluser]OwanH[/eluser]
[quote author="java" date="1183358263"]I tried to instantiate CI but it still generate an error. I dont know it's not understand my query command.[/quote]

Make sure you are loading the Active Record class. In the database configuration file located at:

application/config/database.php

make sure the following variable is set to TRUE:

Code:

$db['default']['active_r'] = TRUE;

where 'default' is the name of your active database group.