Polecat as Event Store

Polecat provides a full-featured event store built on SQL Server 2025, following the same patterns as Marten's PostgreSQL-based event store.

Key Concepts

• Event -- An immutable record of something that happened in your domain
• Stream -- A sequence of events related to a specific aggregate or entity
• Aggregate -- A domain object whose state is derived by replaying events
• Projection -- A read model built from events, either inline, live, or asynchronously

Event Store Tables

Polecat uses three core tables (all prefixed with pc_):

Table	Purpose
pc_events	All events with sequence IDs, stream references, JSON data
pc_streams	Stream metadata: version, type, timestamps, snapshots
pc_event_progression	Async daemon progress tracking per projection

Stream Identity

Streams can be identified by either Guid or string:

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

    // Default: Guid stream IDs
    opts.Events.StreamIdentity = StreamIdentity.AsGuid;

    // Alternative: String stream IDs
    opts.Events.StreamIdentity = StreamIdentity.AsString;
});

Quick Example

// Define events
public record InvoiceCreated(decimal Amount, string Customer);
public record InvoicePaid(decimal AmountPaid, DateTimeOffset PaidAt);

// Append events
await using var session = store.LightweightSession();
var streamId = session.Events.StartStream<Invoice>(
    new InvoiceCreated(100m, "Acme Corp"),
    new InvoicePaid(100m, DateTimeOffset.UtcNow)
);
await session.SaveChangesAsync();

// Replay to aggregate
var invoice = await session.Events.AggregateStreamAsync<Invoice>(streamId);

See the Quick Start for a complete walkthrough.

Projection Strategies

Strategy	When Applied	Use Case
Inline	Same transaction as event append	Strong consistency requirements
Live	On-demand replay	Occasional reads, always current
Async	Background daemon	Eventually consistent read models

Event Appending

Polecat uses QuickAppend -- direct SQL INSERT statements with an UPDATE...OUTPUT pattern for version management. No stored procedures are used.

See Appending Events for details.