Searching multiple tables - fields

I only focussed on the logic for searching in your database, not on the form you provide your users with. I assumed that you already managed to do that part yourself.

The 2 examples I shared:

PHP Code:

$data['city'] = 'New York';  //example of city in your search box
$data['category'] = 15;    //example of category_id in your search box 


were just meant to be able to test the model function, with query builder commands inside it.
In real life, $data['city'], $data['category'] and $data['name'] must get their values from your form.
There is no need for IF statements in your controller. You collect all values in $this->input->post(), put them in the $data array, and pass that to the model. The model function I wrote, detects which search variables have a value, and which haven't.