teast/simplecqrs

An simple implementation of the "CQRS" pattern

Teast.SimpleCQRS

This is a simple "CQRS"/EventStore implementation that can be used to simplify the boiling plates when building such solutions.

Nuget package

To build nuget package and publish it you can do following commands:

dotnet pack src/SimpleCQRS/
dotnet nuget push src/SimpleCQRS/bin/Release/Teast.SimpleCQRS.0.0.1-preview3.nupkg --api-key <redacted> --source nuget.org

Implementation

The idea is to have Command objects that drives changes to your entity. One implementation is to create an CommandHandler class that can handle your Commands and that uses your Aggregate to generate an corresponding Event object.

Difference between Command and Event

The main different between this two objects is that a Command should be validated and can be rejected while an Event should never be validated and instead always be applied. A Command that is accepted should generate an Event and the Event is the one that should be stored in your data storage and then later on read from data storage when you re-play your entity through an Aggregate

Difference between snapshot and projection

a projection should always represent latest state of your entity while a snapshot can be from any state of your entity.

IStorage

This interface is the glue between Simple.CQRS and your data storage. When Repository needs to fetch events, snapshot, versions, etc from the data storage it will use an object that implements this interface.

Repository

This abstract class will take care of extracting changes from an existing Aggregate for saving to data storage or to create an Aggregate based of data fetched from IStorage.

Aggregate

Aggregate handles creation of events and to load events.

Event

Represents an change to your entity. All changes that you support should inherit from Event

Data

This class represents an snapshot (or projection) of your entity. It is possible to use SimpleCQRS without having an dedicated snapshot class.

Samples

UserApi

This WebApi demonstrates how you can use SimpleCQRS with Entityframework Core as database storage.

The entity in this example is an User entity where you can change the user's name, email or age through commands. You can also create an user through the CreateCommand.

The Data object in this example is used as an projection instead of an snapshot object. That simplifies the "GET" calls where I can read directly from the projection table.