Laravel 4：计算其中的关系

I have 2 tables as below:

Subscription table have a entrance_limit column, and it has a hasMany('Attendance') relationship. The entrance_limit column will actually limit the number of rows in Attendance. For example, if the entrance_limit value is 10, then we only can create 10 rows in Attendance.

Attendance table has a belongsTo('Subscription') relationship.

How do I get the list of Subscription that have total number of Attendance less than the entrance_limit value?

Subscription::whereHas('attendances', function($q) {
    ## something like this
    $q->count() < subscription->entrance_limit
})

Finally able to get it working with the following:

Subscription::whereRaw('
    (select count(*) from `attendances` where `attendances`.`subscription_id` = `subscriptions`.`id`) < `subscriptions`.`entrance_limit`
');

Model your query has below

Subscription::whereHas('attendances', function($q) {
    $q->where('entrance_limit','>',$q->count());
})