How i can use model in other model?

[eluser]jurosik[/eluser]
Maybe I should write more...

I had one big model with all functions, but now i need to make this model more comprendious, so i allocate my functions into tematic models. but functions have calls between models.

I need to load model once, and then just call them anywhere in model...

Code:

model1
   load model2 (model3, 4...)

function1() {

   model2->function2()

}

i have tried this:

Code:

class Data_model extends Model {

    function Data_model()
    {
        parent::Model();        
        $this->CI =& get_instance();
        $this->CI->load->model('main_model');
        $this->CI->load->model('file_model');
    }

...

$this->CI->main_model->getSomething($value);

But when i load file Data_model in Main_model (here is function 1 which i am calling from Data_model) it doesn't work

Code:

class Main_model extends Model {

    function Main_model()
    {
        parent::Model();
        $this->CI =& get_instance();
        $this->CI->load->model('data_model');
        $this->CI->load->model('file_model');
    }

    function getSomething($value)
    {
        return $value;
    }
}

mybe it's very complicated to explain...