Event Metadata

See Marten Metadata for more information and examples about capturing metadata as part of IDocumentSession unit of work operations.

The metadata tracking for events can be extended in Marten by opting into extra fields for causation, correlation, and key/value headers with this syntax as part of configuring Marten:

var store = DocumentStore.For(opts =>
{
    opts.Connection("connection string");

    // This adds additional metadata tracking to the
    // event store tables
    opts.Events.MetadataConfig.HeadersEnabled = true;
    opts.Events.MetadataConfig.CausationIdEnabled = true;
    opts.Events.MetadataConfig.CorrelationIdEnabled = true;
});

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The actual metadata is accessible from the IEvent interface event wrappers as shown below (which are implemented by internal Event<T>):

public interface IEvent
{
    /// <summary>
    ///     Unique identifier for the event. Uses a sequential Guid
    /// </summary>
    Guid Id { get; set; }

    /// <summary>
    ///     The version of the stream this event reflects. The place in the stream.
    /// </summary>
    long Version { get; set; }

    /// <summary>
    ///     The sequential order of this event in the entire event store
    /// </summary>
    long Sequence { get; set; }

    /// <summary>
    ///     The actual event data body
    /// </summary>
    object Data { get; }

    /// <summary>
    ///     If using Guid's for the stream identity, this will
    ///     refer to the Stream's Id, otherwise it will always be Guid.Empty
    /// </summary>
    Guid StreamId { get; set; }

    /// <summary>
    ///     If using strings as the stream identifier, this will refer
    ///     to the containing Stream's Id
    /// </summary>
    string? StreamKey { get; set; }

    /// <summary>
    ///     The UTC time that this event was originally captured
    /// </summary>
    DateTimeOffset Timestamp { get; set; }

    /// <summary>
    ///     If using multi-tenancy by tenant id
    /// </summary>
    string TenantId { get; set; }

    /// <summary>
    ///     The .Net type of the event body
    /// </summary>
    Type EventType { get; }

    /// <summary>
    ///     Marten's type alias string for the Event type
    /// </summary>
    string EventTypeName { get; set; }

    /// <summary>
    ///     Marten's string representation of the event type
    ///     in assembly qualified name
    /// </summary>
    string DotNetTypeName { get; set; }

    /// <summary>
    ///     Optional metadata describing the causation id
    /// </summary>
    string? CausationId { get; set; }

    /// <summary>
    ///     Optional metadata describing the correlation id
    /// </summary>
    string? CorrelationId { get; set; }

    /// <summary>
    ///     Optional user defined metadata values. This may be null.
    /// </summary>
    Dictionary<string, object>? Headers { get; set; }

    /// <summary>
    ///     Has this event been archived and no longer applicable
    ///     to projected views
    /// </summary>
    bool IsArchived { get; set; }

    /// <summary>
    ///     Marten's name for the aggregate type that will be persisted
    ///     to the streams table. This will only be available when running
    ///     within the Async Daemon
    /// </summary>
    public string? AggregateTypeName { get; set; }

    /// <summary>
    ///     Set an optional user defined metadata value by key
    /// </summary>
    /// <param name="key"></param>
    /// <param name="value"></param>
    void SetHeader(string key, object value);

    /// <summary>
    ///     Get an optional user defined metadata value by key
    /// </summary>
    /// <param name="key"></param>
    /// <returns></returns>
    object? GetHeader(string key);
}

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