Implementing Event Sourcing in .NET

Implementing Event Sourcing in .NET

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  Implementing Event Sourcing in.NET Andrea Saltarello CEO @ managed/designs andysal@gmail.com http://twitter.com/andysal74 http://slideshare.net/andysal
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  Who I am 1.CEO @ Managed Designs, striving to discover the perfect «sustainable software development process» • Customer has to be satisfied and pay • Supplier has to have a reasonable markup • Team members should be satisfied with their work 2. Founder and leader of UGIdotNET (first Italian .NET User Group): I need to share experiences in a peer to peer way 3. (Co)Author (together with Dino) of .NET: Architecting Applications for the Enterprise, by Microsoft Press 4. Basically, a software developer 
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  CQRS recap Query Command
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  DEMO CQRS recap
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  It really becameclear to me in the last couple of years that we need a new building block and that is the Domain Event. [Eric Evans] An event is something that has happened in the past. [Greg Young] A domain event … captures the memory of something interesting which affects the domain [Martin Fowler]
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  Why events? «Undo principle»:Instead of focusing on a system’s last known state, we could note down every occurring event: this way, we would be able build the state the system was in at any point in time To cut a long story short: we end up recording an event stream JobOrderCreated InvoiceIssuedJobOrderExtended JobOrderClosed
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  Event Stream vs.«My application» Still, my users are more interested in knowing a job order’s balance or whether an invoice has been paid. Ways to achieve that: • Rebuilding the state traversing the whole event stream (slow, but snapshots can help) • CQRS to the rescue: let’s have a database dedicated to store the last known state and have it read by the read model
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  CQRS/ES in anutshell 1. Application sends a command to the system 2. Command execution alters the system’s state and raises events to state success/failure 3. Events are notified to interested subscribers, such as: • Workflow managers (a.k.a. «Sagas») which can execute more commands • Denormalizers, which will update the read model Note: command/event dispatch will usually be managed by a Mediator («bus»)
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  Read Model Application Layer Domain layer Event store QUERY COMMAND Bus EVENT Handler Handler Handler Snapshot DB CQRS/ES ata glance
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  DEMO Merp
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  On a technologyside… Looking for a bus and an event store: build or buy? • Event Store: –SQLWhatever –MongoDB –RavenDB • Bus: –NEventStore –NServiceBus My advice? Buy #donoteverthinkaboutmakingyourowntoolkit
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  The “Buy” Sideof the Force SQLWhatever MongoDB RavenDB • Everyone’s skill • Every tool you can need does exist • Both On-Premise & cloud • Free • Runs on both Linux and Windows • Both On-Premise & cloud • Schemaless • LINQ support • TX+DTC support • Schemaless • Both On-Premise & cloud MSMQ NEventStore NServiceBus • ROTFL • Free • FOSS • DDD/CQRS/ES full stack • Advances config options • Advanced notifications features
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  DEMO NServiceBus
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  Bibliography [DDD] Domain DrivenDesign, Eric Evans , Addison-Wesley What I've learned about DDD since the book, Eric Evans, InfoQ [NAAE] Microsoft .NET: Architecting Applications for the Enterprise (2° ed.), Andrea Saltarello & Dino Esposito, Microsoft Press [MERP] Merp, https://naa4e.codeplex.com/