Notification Service design

In this section is presented the abstract design of the notification service.

As already presented, its main responsibility is to send notifications to the users, based on the events that occur in the system.

Structure link

The structure of the service is quite simple:

• Token is a value object that represents the token used to identify the device of a user.
• UserToken is an entity that represents the association between a user and a token.
• UsersTokensService is the service that allows registering and invalidating tokens for users.
• UsersTokensRepository is the repository that stores the associations between users and tokens.
• NotificationPublisher is the service that sends notifications to users.
  • PublishingTargetStrategy is the strategy used to determine the target of the notification. Two stategies exists: one to send to all members of a group (corresponding to the GroupWisePushNotification command) and another to send to all members sharing a group with a user (corresponding to the CoMembersPushNotification command).
• GroupsRepository is the repository that allows storing and retrieving the members of the groups. This is called by the message broker adapter on every events whose topic is related to groups state changes.

Interaction link

The main flow scenario is describe below and depicted in the following sequence UML diagram.

Each group member registers its device token to the notification service through an external infrastructural component that will handle the reliable delivery of the notification to the device. Here it is abstracted away as PushNotificationInfrastructure. This token is stored in the UsersTokensRepository and associated with the user id. When a notification command is received, the NotificationPublisher retrieves the members of the group and sends the notification to each member’s device.