Migration from 1.7.2 to 2.0 and respectively to 3.0

It was very interesting very very intresting case. A file I have added was listed as missing I mean the file was there but the code somehow could not read it. I just uploaded it again but now I have a new problem.

I updated all files and when Controller or Model is called, I should extend CI_Controller or CI_Model, but it gives me error, and when I changed it ot Controller or Model only it worked. But now I get this error ->

Call to undefined method CI_DB_mysql_driver::order_by()

And I think it's because I've missed something. I've written

$active_group = "default";
$active_record = TRUE;

But it's not working.
I don't have datamapper so I cannot ad it in the index.

What should I do to get rid of this problem?

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