Open Event

This post discusses about the Organizer Server Permissions System and how it has been implemented using database models.

The Organizer Server Permissions System includes Roles, and Services that these roles can access. Roles can broadly be classified into Event-specific Roles and System-wide Roles.

System-Wide Roles

System-wide roles can be considered a part of the staff maintaining the platform. We define two such roles: Admin and Super Admin. The Super Admin is the highest level user with permissions to access system logs, manage event-specific roles, etc.

System-wide roles are the easiest to implement. Since they’re directly related to a user we can add them as class variables in the User models.

class User(db.Model):
    # other stuff

    is_admin = db.Column(db.Boolean, default=False)
    is_super_admin = db.Column(db.Boolean, default=False)

    @property
    def is_staff(self):
        return self.is_admin or self.is_super_admin

Staff groups Admin and Super Admin roles. So to check if a user is a part of the staff (an admin or a super admin), the is_staff property can directly be used.

user.is_staff

Event-Specific Roles

An Event itself can contain many entities like Tracks, Sponsors, Sessions, etc. Our goal was to define permissions for Roles to access these entities. We grouped these entities and put them under “Services”. Services are nothing but database models associated with an event, that need to have restricted access for the Roles.

We define the following Services for an Event:

• Track
• Session
• Speaker
• Sponsor
• Microlocation

Each of these services can either be created, read, updated or deleted. And depending on the Role a user has been assigned for a particular event, he or she can perform such operations.

There are four Event-Specific Roles:

• Organizer
• Co-organizer
• Track Organizer
• Moderator

As soon as the user creates an event, he is assigned the role of an Organizer, giving him access to all the services for that event. An Organizer can perform any operation on any of the services. A Co-organizer also has access to all the services but can only update them. A Track Organizer can just read and update already created Tracks. The Moderator can only read Tracks.

Although the initial distribution of permissions is kept as above, the Super Admin can (has permissions to) edit them later.

To implement permissions for Event specific roles, three new database models were required: Role, Service and Permission.

Role and Service would contain the above mentioned Roles and Services respectively. Permission would contain a Role column, a Service column and four other columns specifying what operation (create/read/update/delete) that Role is allowed to perform on the Service.

The final objective was to define these methods for the User class:

user.can_create(service, event_id)
user.can_read(service, event_id)
user.can_update(service, event_id)
user.can_delete(service, event_id)

Before this we needed a table specifying what Event Roles have been created for an event, and which users have been assigned these roles. The `UsersEventsRoles` model maintained this relationship.

We also needed to check if a user has been assigned a particular role for an event. For this I created a method for each of the roles.

# Event-specific Roles
ORGANIZER = 'organizer'
COORGANIZER = 'coorganizer'
TRACK_ORGANIZER = 'track_organizer'
MODERATOR = 'moderator'

class User(db.Model):
    # other stuff

    def _is_role(self, role_name, event_id):
        role = Role.query.filter_by(name=role_name).first()
        uer = UsersEventsRoles.query.filter_by(user=self,
                                               event_id=event_id,
                                               role=role).first()
        if not uer:
            return False
        else:
            return True

    def is_organizer(self, event_id):
        return self._is_role(ORGANIZER, event_id)

    def is_coorganizer(self, event_id):
        return self._is_role(COORGANIZER, event_id)

    def is_track_organizer(self, event_id):
        return self._is_role(TRACK_ORGANIZER, event_id)

    def is_moderator(self, event_id):
        return self._is_role(MODERATOR, event_id)

Here _is_role helps reduce code redundancy.

Like I said, our final objective was to create methods that determine if a user has permission to perform a particular operation on a service based on the role, I defined the following methods:

    # ...`User` class

    def _has_perm(self, operation, service_class, event_id):
        # Operation names and their corresponding permission in `Permissions`
        operations = {
            'create': 'can_create',
            'read': 'can_read',
            'update': 'can_update',
            'delete': 'can_delete',
        }
        if operation not in operations.keys():
            raise ValueError('No such operation defined')

        try:
            service_name = service_class.get_service_name()
        except AttributeError:
            # If `service_class` does not have `get_service_name()`
            return False

        service = Service.query.filter_by(name=service_name).first()

        uer_querylist = UsersEventsRoles.query.filter_by(user=self,
                                                         event_id=event_id)
        for uer in uer_querylist:
            role = uer.role
            perm = Permission.query.filter_by(role=role,
                                              service=service).first()
            if getattr(perm, operations[operation]):
                return True

        return False

    def can_create(self, service_class, event_id):
        return self._has_perm('create', service_class, event_id)

    def can_read(self, service_class, event_id):
        return self._has_perm('read', service_class, event_id)

    def can_update(self, service_class, event_id):
        return self._has_perm('update', service_class, event_id)

    def can_delete(self, service_class, event_id):
        return self._has_perm('delete', service_class, event_id)

The can_create, can_read, etc. defined in operations are the four columns in the Permission db model. Like _is_role, _has_perm method helps implementing the DRY philosophy.