mysql - grocery crud with AES Encryption -

how match data in table using mysql aes decrypt in grocery crud ?

error getting on crud set realtion follows:

$crud->set_relation(aes_decrypt(departments.department_id,'key'),'users.department_id','deparmtnet_name'); 

not found: departments.aes_decrypt(departments.department_id,'key')

select user_name,department_name users j333 left join departments jd333 on departments.aes_decrypt(departments.department_id,'key')=j333.department_id 

grocery crud doesn't recognize "aes decrypt" function