Introduction

Welcome to the Polecat documentation!

What is Polecat?

Polecat is a .NET library for building applications using a document-oriented database approach and Event Sourcing, backed by SQL Server 2025.

Polecat is part of the Critter Stack ecosystem and mirrors the API patterns of Marten (the PostgreSQL equivalent), making it easy for teams already familiar with Marten to adopt SQL Server as their backing store.

TIP

If you've used Marten before, you'll feel right at home with Polecat. The API surface is intentionally similar -- same interface names, same session patterns, same projection model.

Under the hood, Polecat is built on top of SQL Server 2025, leveraging its native JSON type to provide:

• a document database,
• an event store.

Polecat uses SQL Server 2025's native JSON data type for storing document bodies, event data, headers, and snapshots. Combined with modern T-SQL features, this provides strong data consistency for both document storage and event sourcing approaches.

Main Features

Feature	Description
Document Storage	Store your entities as JSON documents in SQL Server with full LINQ querying support.
Event Store	Full-fledged event store for Event Sourcing with stream management, projections, and subscriptions.
Strong Consistency	Uses SQL Server transactions for ACID compliance across both document and event operations.
LINQ Querying	Filter documents using LINQ queries with string searching, child collection queries, paging, and more.
Event Projections	Build read models from events using inline, async, or live projection strategies.
Automatic Schema Management	Polecat manages SQL Server table creation and migrations automatically via Weasel.SqlServer.
Optimistic Concurrency	Built-in support for both Guid-based and numeric revision concurrency control.
Multi-Tenancy	Multiple tenancy strategies: conjoined (same tables), separate databases, or single tenant.
Async Daemon	Background projection processing for eventually consistent read models.
EF Core Integration	Use Entity Framework Core DbContext within your event projections.

Critter Stack Ecosystem

Polecat is designed to work alongside other Critter Stack libraries:

Library	Purpose
Marten	PostgreSQL document database and event store
Wolverine	Messaging and command processing framework
JasperFx	Core framework and event sourcing abstractions
Weasel	Database schema management

Polecat vs Marten

Polecat mirrors Marten's API but targets SQL Server 2025 instead of PostgreSQL:

Feature	Marten (PostgreSQL)	Polecat (SQL Server)
JSON storage	jsonb type	json type (SQL Server 2025)
Sequences	bigserial / sequences	bigint IDENTITY(1,1)
Upsert	INSERT ... ON CONFLICT	MERGE statement
Change notification	LISTEN/NOTIFY	Polling (configurable interval)
Advisory locks	pg_advisory_lock	sp_getapplock / sp_releaseapplock
Timestamps	timestamptz	datetimeoffset
Serialization	STJ or Newtonsoft	System.Text.Json only

History and Origins

The project name Polecat follows the Critter Stack tradition of naming projects after animals. A polecat is a member of the mustelid family -- close relatives of the marten, making it a fitting name for Marten's SQL Server cousin.