No search for existance of a relation is available

[drmheydari]

Some of users of model Student have foreign key to model User. I create relation student() in model User with hasOne() to join them. Now in model User I need to filter those who are student. How can I do that?

I tried
public $searchable = ['name', 'mobile', 'email', 'id', 'student:id'];

and in string query I set

student:id=(null)

and doesn't work because the relation doesn't exist in the first place.