Appending an event to the event log

The event log is the primary event sequence in Cratis. It is the source of truth we use privately to derive all other results from.

Appending to it requires you to get a hold of the client representation of the event log and calling append on it. This is done by taking a dependency to IEventLog from the Cratis.Events namespace.

Assuming you have an event as defined here, you can do the following:

using Cratis.Events;

public class DebitAccounts(IEventLog eventLog)
{
    public Task OpenDebitAccount(AccountName Name, CustomerId Owner) =>
        eventLog.Append(Guid.NewGuid().ToString(), new DebitAccountOpened(Name, Owner));
}

Note: The first parameter of Append() takes the type EventSourceId. This is a wrapper for a string value type. The EventSourceId is the identifier that identifies the unique instance of a concept in your domain, often referred to as an aggregate.

Since Chronicle does not provide a centralized key generator, it is common to use a Guid that can be generated on the fly. This is very common in modern systems, as it removes tension in inserts. The EventSourceId type provides an implicit conversion from Guid to EventSourceId.

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Appending an event to the event log