What is Event Sourcing in C#

Introduction to Event Sourcing
Event sourcing is a software architecture pattern that captures and represents changes to an application’s state as a sequence of events. These events can be stored and replayed to reconstruct the state of the application at any point in time. In this article, we will explore the concept of event sourcing and how it can be implemented in C#.

How Does Event Sourcing Work?
In event sourcing, instead of directly persisting the current state of an object, we store a sequence of events that represent changes to the object’s state. Each event is an immutable record that describes a specific change or action that occurred in the system. These events are stored in an event store, which acts as a log of all the application’s past events.

Benefits of Event Sourcing
Event sourcing offers several benefits over traditional approaches to data persistence and state management. Some of the key advantages include:

• Auditing and traceability: Since all the events are stored in a log, it’s easy to trace back and audit how the system reached its current state.
• Time-traveling and replayability: By replaying the events in the correct sequence, we can recreate the application’s state at any given point in time.
• Flexible querying and reporting: Since events contain all the necessary information, we can easily query and analyze data in various ways.
• Scalability and parallel processing: Event sourcing supports parallel processing and scaling by having multiple event consumers and event handlers.

Implementing Event Sourcing in C#
To implement event sourcing in C#, we need to define event classes that represent changes to the application’s state. Each event class should inherit from a base event class or interface and contain properties to hold relevant data. We also need an event store to persist and retrieve the events.

Example Event Class

public class OrderCreatedEvent : IEvent
{
    public Guid OrderId { get; set; }
    public DateTime CreatedAt { get; set; }
    // Other relevant properties
}

Example Event Store Implementation

public interface IEventStore
{
    void AppendEvent(IEvent @event);
    IEnumerable<IEvent> GetEventsByAggregateId(Guid aggregateId);
    // Other necessary methods
}

public class SqlEventStore : IEventStore
{
    public void AppendEvent(IEvent @event)
    {
        // Append the event to the SQL database
    }

    public IEnumerable<IEvent> GetEventsByAggregateId(Guid aggregateId)
    {
        // Retrieve events by aggregate ID from the SQL database
        return events;
    }
}