Relation Limit [ octobercms ]

Question

I have a model called Lessons and it has a belongsToMany relationship called students with a table called students_for_lesson . Lesson model has fields called number_of_students and number_of_enrollments for each lesson.

what I want is to give a message stopping Add students for the lesson when number_of_enrollments value reaches number_of_students value.

Answer 1

One way is to listen to the Model relation events ( BelongsToMany ) : beforeAttach , afterAttach , beforeDetach , afterDetach

In this case if you need to run some validations before creating the relationship then use the beforeAttach event:

LessonModel::extend(function ($model) {

    /** Before Attach */
    $model->bindEvent('model.relation.beforeAttach', function ($relationName, $attachedIdList, $insertData) use ($model) {

        // Student => Lesson Relation
        if ($relationName === 'your-lesson-student-relation-name') {

            // Check Number of enrollments & other stuff ...

            // throw new \ApplicationException('Cannot add student. Maximum number of enrollments reached.');
        }

    });

});

See this SO post & here about extending models