codeigniter - Why protect tables and fields on top of every model? -

i have seen codeigniter application coder protected table , fields @ tp of every model. why this? , maybe why protect primary key separate other fields?

class students_model extends my_model{     protected $table = 'students';     protected $primary_key = 'id';     protected $columns = array(                                      'student_code'          =>  array('code',    'trim|required'),         'student_name'          =>  array('name',    'trim|required'),         'country'               =>  array('country', 'trim|required'),                                       ); } 

this question understanding best practices in mvc (not codeigniter). there few different things going on here.

1) "protected" prolly done out of habit. protected php class keyword, , has nothing ci or models. can read here: http://jp2.php.net/protected; if after reading don't understand why used in case, it's because there isn't reason use in case.

2) key understanding rest "extends my_model". my_model base model object normal crud functions , utilities written; inherit it. however, our my_model have function get_all() say:

$this->db->from($this->table)->get(); 

for example. so, in our students model set $this->table = "students", above code translates to:

$this->db->from('students')->get();   

but other models can pass different table name. able make simple table specific models , share more complex logic via my_model

you can see going #1, unlikely we'll ever inherit students_model, protected isn't harming anything, isn't terribly necessary

3) $columns in case validation rules; whichever my_model being used here adding validation functions my_model instead of putting on controllers