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Marten DCB Implementation Summary

Shared Types (JasperFx.Events)

  • EventTag — readonly record struct(Type TagType, object Value) stored on each event
  • TagTypeRegistration — Wraps a strong-typed ID type (e.g. StudentId(Guid Value)) with ValueTypeInfo, TableSuffix, SimpleType, and optional AggregateType
  • EventTagQuery — Builds OR'd conditions of (EventType?, TagType, TagValue) via fluent Or<TTag>(value) API
  • IEvent.WithTag() — Extension methods to attach tags to events; uses TagValueExtractor (compiled lambdas) to unwrap inner values

Schema & Registration

  • EventGraph — Holds List<TagTypeRegistration>, exposes RegisterTagType<T>(), FindTagType(), TagTypes
  • EventTagTable — One table per tag type: mt_event_tag_{suffix} with composite PK (value, seq_id), FK to mt_events.seq_id. Value column type maps from SimpleType (Guid→uuid, string→text, int→integer, etc.)
  • EventGraph.FeatureSchema — Yields EventTagTable instances in schema object generation

Tag Insert Operations (3 paths)

  1. InsertEventTagOperation — Rich mode: direct INSERT (value, seq_id) VALUES (...) using pre-assigned sequence
  2. InsertEventTagByEventIdOperation — Quick mode fallback: INSERT ... SELECT seq_id FROM mt_events WHERE id = @eventId for individual insert paths (Start/ExpectedVersion)
  3. QuickAppendEventFunction — Quick mode optimized: tag value arrays passed as varchar[] parameters to the PL/pgSQL function; tags inserted inline in the same loop using the already-available seq variable
  • EventTagOperations — Static helper dispatching to QueueTagOperations() (Rich) or QueueTagOperationsByEventId() (Quick individual paths)

Code Generation (Quick Append)

  • EventDocumentStorageGenerator.buildQuickAppendOperation() — Conditionally emits writeAllTagValues(parameterBuilder) when graph.TagTypes.Count > 0
  • QuickAppendEventsOperationBase.writeAllTagValues() — Builds parallel string?[] arrays per tag type from event tags, appends as NpgsqlDbType.Array | Varchar
  • QuickEventAppender — Routes: function path skips separate tag ops (handled in-function); Start/ExpectedVersion paths queue InsertEventTagByEventIdOperation

Query & Consistency

  • EventStore.Dcb.cs — Session APIs: QueryByTagsAsync(), AggregateByTagsAsync<T>(), FetchForWritingByTags<T>(). Builds SQL with INNER JOINs to tag tables + OR'd WHERE conditions
  • AssertDcbConsistency — IStorageOperation queued at fetch time, runs at SaveChangesAsync: EXISTS query checks for events with seq_id > lastSeenSequence matching the tag query. Throws DcbConcurrencyException if violated
  • IEventBoundary<T> / EventBoundary<T> — Wraps query result: Aggregate, Events, LastSeenSequence. AppendOne()/AppendMany() route new events to streams by tag values
  • FetchForWritingByTagsHandler<T> — IQueryHandler for batch query support; same SQL building + assertion registration

Batch Querying

  • IBatchEvents.FetchForWritingByTags<T>() — Interface on IBatchedQuery
  • BatchedQuery.Events.cs — Delegates to FetchForWritingByTagsHandler<T> via AddItem()

Key File Locations

JasperFx.Events (shared)

File Purpose
JasperFx.Events/EventTag.cs Core tag value type
JasperFx.Events/Tags/TagTypeRegistration.cs Tag type registration & value extraction
JasperFx.Events/Tags/EventTagQuery.cs Query specification with OR'd conditions
JasperFx.Events/IEvent.cs WithTag() extension methods
JasperFx.Events/Event.cs Tag storage on event instances

Marten

File Purpose
Marten/Events/EventGraph.cs RegisterTagType<T>(), tag type list
Marten/Events/EventGraph.FeatureSchema.cs Schema generation for tag tables
Marten/Events/Schema/EventTagTable.cs Tag table DDL (per tag type)
Marten/Events/Schema/QuickAppendEventFunction.cs PL/pgSQL function with inline tag inserts
Marten/Events/Operations/InsertEventTagOperation.cs Rich mode tag insert
Marten/Events/Operations/InsertEventTagByEventIdOperation.cs Quick mode tag insert (by event ID)
Marten/Events/Operations/EventTagOperations.cs Static tag operation dispatcher
Marten/Events/Operations/QuickAppendEventsOperationBase.cs writeAllTagValues() for function path
Marten/Events/QuickEventAppender.cs Append routing (function vs individual)
Marten/Events/CodeGeneration/EventDocumentStorageGenerator.cs Conditional tag codegen
Marten/Events/EventStore.Dcb.cs Session-level DCB APIs
Marten/Events/Dcb/IEventBoundary.cs Public boundary interface
Marten/Events/Dcb/EventBoundary.cs Boundary implementation & event routing
Marten/Events/Dcb/AssertDcbConsistency.cs Consistency check operation
Marten/Events/Dcb/DcbConcurrencyException.cs Concurrency violation exception
Marten/Events/Dcb/FetchForWritingByTagsHandler.cs Batch query handler
Marten/Services/BatchQuerying/BatchedQuery.Events.cs Batch query integration