MongoZen

MongoDB is nice and all, but the driver experience in C# usually sucks. You either end up with reflection-heavy "automagical" repositories, or you're writing manual BsonDocument boilerplate for aggregation pipelines like it's 2010.

MongoZen gives you the RavenDB Experience on top of MongoDB:

1. Zero-Allocation Shadow Tracking: No cloning object graphs. We use raw BSON bytes in an Arena as the baseline.
2. True Unit of Work: A scoped session with an Identity Map and automatic change detection.
3. Blittable Performance: A custom BSON engine that is up to 171x faster at parsing than the official driver.
4. RavenDB-style API: LoadAsync, Store, SaveChangesAsync, and a first-class Attachments API.

Quick Start

1. Initialize the Store

var store = new DocumentStore("mongodb://localhost:27017", "MyDatabase");

2. Basic Session Usage

using var session = store.OpenSession();

// Load a document (snapshot is captured in Arena memory)
var user = await session.LoadAsync<User>("users/1");

// Mutate the POCO
user.Name = "Oren Eini";
user.LastLogin = DateTime.UtcNow;

// Persist changes (only modified fields are sent via $set)
await session.SaveChangesAsync();

3. Attachments API

// Store a large blob linked to a document
using var stream = File.OpenRead("profile.jpg");
await session.Attachments.StoreAsync("users/1", "avatar.jpg", stream, "image/jpeg");

// Retrieve it
using var attachment = await session.Attachments.GetAsync("users/1", "avatar.jpg");
Process(attachment.Stream);

// Attachments are automatically scrubbed if the document is deleted!
session.Delete(user);
await session.SaveChangesAsync(); // Deletes document AND its GridFS files

Architectural Tiers

• Tier 1 (Source Gen): Compile-time non-allocating diffing.
• Tier 2 (Dynamic Reflection): Compiled Expression Trees for zero-allocation runtime serialization.
• Tier 3 (Driver Bridge): 100% compatibility fallback for complex custom driver configurations.

Performance vs. Official Driver

Operation	Gain
BSON Parsing/Indexing	~171x Faster (Zero GC)
Serialization	~1.9x Faster (~100% less GC)
Identity Map	O(1) lookup, Zero allocation

License

MIT. Go build something fast.