Extending own class in PHP CodeIgniter 3 -

i have 2 models: models/categories.php , models/backend/be_categories.php

i want be_categories class extend categories, since has useful functions can re-use:

categories.php

class categories extends ci_model { ... 

be_categories.php

class be_categories extends categories { ... 

but when $this->load->model('models/be_categories') error: unable locate specified class: session.php yet works exending ci_model have done wrong?

just guess, load session library inside function in categories model,and try use function session library specific function inside model be_categories.

add session library in config/autoload.php or load inside categories model constructor, , remember add constructor inside be_categories.