Event Store Projections – The irresponsible gambler

Imagine a world where online gambling sites were nice enough to notify you when you’re gambling irresponsibly: if you’d spend too much money, they’d take notice and send you an alert via email or text message. Of course, online gambling sites bank on people being just so frivolous with their money, but there’s nothing stopping us from dreaming – or from implementing such a system as our next example.

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First off, we’ll assume we have a Game aggregate which raises a GameOver that contains a list of the players that participated in the game and the amounts they lost or won.

Our irresponsible gambler alarm system needs three projections. The first projection will distribute the GameOver events to GameWon and GameLost events emitted to all participating players. The second projection is a temporal projection that will generate alarms based on the results of all games played in the last 24 hours. The last projection, implemented in C#, will send emails and text messages to any players who lost more than 500€ in the last 24 hours, our eponymous irresponsible gamblers. To process these alarms, we will publish all alarms generated in the second projection on a bus in C#.

You can find the projections here:

• The GameOver to player event Distributor
• The IrresponsibleGambling Detector
• The IrresponsibleGamblerAlarm Publisher

EventStore Projections by Example

This post is part of a series:

1. EventStore Client API Basics (C#)
2. Counting events of a specific type
3. Partition events based on data found in previous events
4. Calculating an average per day
5. The irresponsible gambler
6. Distribute events to other streams
7. Temporal Projection to generate alarms
8. Projection in C#