Skip to content

Metadata

Metadata is all the "additional" information that resides with an emitted event, some of which is required information.

In EventFlow, metadata is merely an IEnumerable of KeyValuePair<string,string> for which each is a metadata entry.

Out of the box, these metadata keys are added to each aggregate event:

  • event_name and event_version - A name and version for the event which is used during event deserialization.
  • timestamp - A DateTimeOffset for when the event was emitted from the aggregate.
  • aggregate_sequence_number - The version the aggregate was after the event was emitted, e.g., 1 for the very first event emitted.

Custom metadata provider

If you require additional information to be stored along with each event, you can implement the IMetadataProvider interface and register the class using e.g., .AddMetadataProvider(...) on EventFlowOptions.

Additional built-in providers

EventFlow ships with a collection of ready-to-use providers in some of its NuGet packages.

EventFlow

  • AddEventTypeMetadataProvider

    • event_type_assembly_name - Assembly name of the assembly containing the event.
    • event_type_assembly_version - Assembly version of the assembly containing the event.
    • event_type_fullname - Full name of the event corresponding to Type.FullName for the aggregate event type.

  • AddGuidMetadataProvider

    • guid - A new Guid for each event.

  • AddMachineNameMetadataProvider

    • environment_machinename - Adds the machine name handling the event from Environment.MachineName.