Designing a Scalable Notification System: Models, Services, and Subscriptions

This article continues from the previous part, focusing on the implementation of a messaging system to inspire readers.

Model Design

Notify

id: {type: 'integer', primaryKey: true} // primary key

content: {type: 'text'} // message content

type: {type: 'integer', required: true, enum: [1, 2, 3]} // 1: Announce, 2: Remind, 3: Message

target: {type: 'integer'} // target ID

targetType: {type: 'string'} // target type

action: {type: 'string'} // action type for reminders

sender: {type: 'integer'} // sender ID

createdAt: {type: 'datetime', required: true}

Save Remind

For reminder records we need target, targetType to identify the associated object, and action to record the related action. Example: a reminder "Xiao Ming liked an article" would be stored as:

target = 123 // article ID

targetType = 'post' // indicates the target is an article

sender = 123456 // Xiao Ming's user ID

Save Announce and Message

Announcements and messages use the content field and do not require target, targetType, or action.

UserNotify

id: {type: 'integer', primaryKey: true} // primary key

isRead: {type: 'boolean', required: true}

user: {type: 'integer', required: true} // owner of the notification

notify: {type: 'integer', required: true} // reference to Notify

createdAt: {type: 'datetime', required: true}

UserNotify stores a user's notification queue and links to a specific Notify record. It is created via two pathways:

When iterating the Subscription table to pull announcements and reminders.

Immediately after a new Message is created.

Subscription

target: {type: 'integer', required: true} // target ID

targetType: {type: 'string', required: true} // target type

action: {type: 'string'} // subscription action, e.g., comment, post, update

user: {type: 'integer'} // subscriber

createdAt: {type: 'datetime', required: true}

Subscriptions define which actions on which targets a user wishes to be notified about. Example: "Xiao Ming follows comments on product A" translates to:

target = 123 // product A ID

targetType = 'product'

action = 'comment'

user = 123 // Xiao Ming's ID

SubscriptionConfig

action: {type: 'json', required: true} // user settings

user: {type: 'integer'}

Different users may have different subscription preferences. The default configuration is:

{
  'comment': true,
  'like': true
}

In this model, targetType and action can be extended, e.g., adding actions like hate (downvote) or update .

NotifyConfig

targetType: {

PRODUCT: 'product', // product
POST: 'post' // article
}

action: {

COMMENT: 'comment', // comment
LIKE: 'like' // like
}

reasonAction: {

'create_product': ['comment', 'like'],
'like_product': ['comment'],
'like_post': ['comment']
}

defaultSubscriptionConfig: {

'comment': true,
'like': true
}

Service Layer NotifyService

NotifyService provides the following methods:

createAnnounce(content, sender)

createRemind(target, targetType, action, sender, content)

createMessage(content, sender, receiver)

pullAnnounce(user)

pullRemind(user)

subscribe(user, target, targetType, reason)

cancelSubscription(user, target, targetType)

getSubscriptionConfig(userID)

updateSubscriptionConfig(userID)

getUserNotify(userID)

read(user, notifyIDs)

Method Logic

createAnnounce(content, sender)

Insert a new announcement record into the Notify table.

createRemind(target, targetType, action, sender, content)

Insert a new reminder record into the Notify table.

createMessage(content, sender, receiver)

Insert a new message record into the Notify table.

Insert a corresponding UserNotify record linking to the new Notify.

pullAnnounce(user)

Retrieve the most recent announcement creation time (lastTime) from UserNotify.

Use lastTime as a filter to query new announcements from Notify.

Create UserNotify entries for the fetched announcements.

pullRemind(user)

Fetch the user's subscription records.

For each subscription, use target, targetType, action, and createdAt to query matching Notify records (subscription time must precede reminder creation).

Retrieve the user's SubscriptionConfig; fall back to the default if absent.

Filter the queried Notify records according to the subscription configuration.

Create UserNotify entries for the filtered notifications.

subscribe(user, target, targetType, reason)

Lookup NotifyConfig using the reason to obtain the associated action set.

For each action, create a Subscription record.

cancelSubscription(user, target, targetType)

Delete the Subscription record(s) matching the user, target, and targetType.

getSubscriptionConfig(userID)

Query the SubscriptionConfig table for the user's settings.

updateSubscriptionConfig(userID)

Update the user's SubscriptionConfig record.

getUserNotify(userID)

Retrieve the list of notifications for the user.

read(user, notifyIDs)

Set the isRead attribute to true for the specified notifications.

Sequence Diagrams