A sender posts a message on a named channel to one or more recipients. The posted messages are stored and regularly dispatched to a recipient through a formatter and a provider. The formatters job is to, if needed, format the text of the message, perhaps retrieve and include content or user data. You can group several messages together to reduce the number of messages sent to the recipient. The providers job is to send a formatted message to a recipient by some means, the most common way being sending it as an email. You can have more than one provider for a channel and to let the recipient decide which one that is preferred.
A message is posted to the `
INotifier`. A message can either be configured to be sent immediately or be placed in a message queue that is periodically handled by a scheduled job. Messages to be sent are passed to the `
NotificationDispatcher`. The `
NotificationDispatcher` formats the message using a `
NotificationFormatter` and then sends it using a `
NotificationProvider`. You can create your own formatters and providers.
Every message is sent on a channel (identified by a channel name), which is a namespace that groups messages of a certain kind together. Messages in different channels are not mixed. You can create your own channel by coming up with a name to use when creating messages and providing a formatter that supports it. You can configure whether messages for a specific channel should be sent immediately by adding an instance of `
NotificationChannelOptions` to `
INotificationChannelOptionsRegistry` specifing that messages within this channel should be processed immediately. By default are messages processed periodically by the scheduler.
The sender has no control of how the recipient receives the message. The recipient’s provider preferences for that channel determine how the message is actually sent (at the moment a default preference resolver should be used).
Do not use generic names for channels, providers and formatters because they risk colliding with other names. Prefix the names with something unique.
## Message types
NotificationMessage` – The default message type; handles the message at the next scheduled job or immediately depending on registered options for the channel.
ScheduledNotificationMessage` – Handles the message at the next scheduled job that occurs after the provided time.
DelayedNotificationMessage` – Handles the message at the next scheduled job that occurs after the provided time but provides a delay time instead of an actual time.
A user is an `
INotificationUser` instance with a name and a display name.
To find users, get an instance of `
QueryableNotificationUserService` and use the `
FindAsync` method to find users by part of a name or the `
GetAsync` method to get a specific user by name.
### User preferences
Use an instance of `
INotificationPreferenceRegister` to register a default preference resolver for a channel and a provider. The resolver takes a user's name and returns a provider-specific address (for example, email addresses for the email provider).
## Notification posting
Get an instance of the `
INotifier` interface and use the `
PostNotificationAsync` method to post a message (for one or more recipients) to the message queue. If a message has more than one recipient, it is stored internally as one message for each recipient. Hook into the `
NotificationSaved` and `
NotificationFiltered` events to get feedback on the result of the posting (per message).
## Notification dispatching
NotificationDispatcher` is configured in and triggered by the scheduler or called directly for immediate messages. It retrieves the messages that are waiting to be sent and groups them by recipient and channel. For each group, a formatter and a provider is located (if available) to format and send the messages. If there is a problem sending the messages, they are put back in the waiting queue.
When one (or more) messages are sent, they first are routed through a formatter, which can transform the messages with custom formatting and/or combining several messages into one. A formatter has a name to identify it and a list of names that specifies which channels the formatter supports. If the message has a channel name that matches one of the supported names, that formatter is selected to format the message.
If more than one formatter is found that matches the channel name, no message is sent and an error message is logged.
### Format messages
To create your own formatter, implement the `
INotificationFormatter` interface, give it a name and a list of supported channels. The `
FormatMessagesAsync` method formats, takes, and returns a list of messages. In the simplest case of formatting, the method should just return the incoming messages.
It also can format each message by changing `
Content` (and `
Subject`) or combine several messages into one. Make sure to set the `
ContainedID` to match the IDs of the combined messages. Message IDs that exist in an in-message but not in an out-message are considered completed and removed from the queue. If there is a problem formatting the messages, the formatter throws an exception and those messages are put back into the queue and tried again at the next scheduled job.
A provider is a component for sending notifications using a specific method of communication. The built-in `
EmailNotificationProvider`, for example, handles the sending of emails (for configuration, see [Configuring your email server](🔗)). A provider has a name to identify it and a format-property that specifies the format the provider supports (max length and if it supports HTML).
You can write your own provider by implementing the `
INotificationProvider` interface and optionally the `
INotificationProviderStatus` interface, which lets you enable and disable a provider. The `
SendAsync` method handles the sending of messages, and you should call `
succeededAction` or `
failedAction` for each message.
## Handle notifications
### List notifications
Use the `
IUserNotificationRepository` interface to list notifications with the `
GetUserNotificationsAsync` and `
GetUserNotificationsCountAsync` methods. These methods are used in the Optimizely Content Management System (CMS) user interface to show notifications.
To get formatted messages, implement the `
IUserNotificationFormatter` for one or more channels. When calling `
GetUserNotification(s)Async`, formatting is done depending on the `
You can hook into the `
UserNotificationMissing` event to get a callback when a specified notification cannot be found.
### Mark notifications
You can also use the `
IUserNotificationRepository` interface to mark one or more notifications as read with one of the `
MarkUserNotification(s)AsReadAsync` methods. To listen to read notifications, hook into the `
UserNotificationRead` and `
## Truncate message queue
Notifications are stored in the database and old notifications are deleted by the **Notification Message Truncate** scheduled job, which is set to run every night by default and removes all notifications older than 3 months.