Create a dynamic ICS file that users can subscribe to

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We have a website that users login to, and can then book on to courses. These courses and the bookings are stored in our SQL database against the user's UserID. On the course page the user is able to add the course to their Outlook calendar via a simple ICS file that is generated when the user clicks on the button to add it by submitted the required data into the ICS file within the URL that calls it and then using <%=Request("CourseName")%> in the ICS file itself.

We are now looking to create a new ICS file that a user can subscribe to that will update their Outlook calendar with all of the courses they have signed up for, and will automatically update if/when a course has a change applied to it or if the user signs up to a new course then this will also automatically be added to their calendar. I can work out how to generate an ICS file that will hold all of this data using a similar setup to what I have done for the individual courses above, but I cannot work out how to create an ICS file that automatically updates with new information.

I don't know if I need to;
1. Have a hardcoded ICS file stored on the server for each individual user that is then updated as and when a change is made (I would prefer to avoid this as we have a lot of users)
2. If there is a way I can include a SQL statement within an ICS file that will then get the latest course data for the user on the fly (this is preferred, but testing this option so far has always resulted in errors)
3. Something else I have not thought of yet

Any help would be appreciated on this!

subscription calendar icalendar sql html
1 Answers

Here is the approach we are using to solve a similar problem:

Every time an admin changes an event or a user changes their subscription, we trigger an API call to do two things: (1) notify the relevant users of the changes using an auto-generated iCalendar event (.ics), and (2) update the database with the changes.

We opted to give the users and the administrators the power to trigger event-changes, rather than have a timer that checks and sends out updates, because we wanted to avoid the lag.

As to your question about auto-generating, this requires you to create an event_id, which you re-use in the .ics file, along with a METHOD:REQUEST, which notifies the user's email that you are sending a: (a) new event, or (b) change to a prior event. If you build a dynamic iCalendar script, this is possible. You must capture the "changes" and flow them through to a new .ics request.

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