NServiceBus.Persistence.MongoDb

MongoDB Persistence for NServiceBus Sagas. It handles concurrency using a document versioning scheme.

TODO

• Timeout Persistence

Requirements

To use the saga persister, your IContainsSagaData requires a property that has the [DocumentVersion] attribute. A property containing the [Unique] attribute is also recommended. Example:

public class MySagaData : IContainSagaData
{
    [Unique]
    public string MyEntityId { get; set; }

    [DocumentVersion]
    public int Version { get; set; }
    
    public bool Canceled { get; set; }
    
    public Guid Id { get; set; }
    public string Originator { get; set; }
    public string OriginalMessageId { get; set; }
}

Installation

There are two ways:

• Grab the source and compile it yourself :-)
• Install the NuGet Package NServiceBus.Persistence.MongoDb by typing in the Package Manager Console:

  Install-Package NServiceBus.Persistence.MongoDb
  

Usage

To enable MongoDB persistence, use the MongoDB extention methods when calling Configure.

Method	Documentation
.MongoDbPersistence()	Configures the MongoDB database connection. With no arguments, it automatically uses the connectionString with the name NServiceBus/Persistence/MongoDB.
.MongoDbSagaPersister()	Enables Saga Persister.
.MongoDbSubscriptionStorage()	Enables Subscription Storage

Example configuration:

using NServiceBus;
using NServiceBus.Persistence.MongoDB.Configuration;

namespace Example
{
    public class EndpointConfiguration : IConfigureThisEndpoint, AsA_Publisher, IWantCustomInitialization
    {
        public void Init()
        {
                Configure.With()
                    .DefaultBuilder()
                    .MongoDbPersistence()
                    .MongoSagaPersister()
                    .MongoDbSubscriptionStorage()
                    .UseInMemoryTimeoutPersister();
        }
    }
}

Handling Concurrency With MongoDb

Sagas are a great feature of NServiceBus. The key concurrency safeguards that sagas guarantee (see: http://docs.particular.net/NServiceBus/nservicebus-sagas-and-concurrency) depend heavily on the underlying data store. The two specific cases that NServiceBus relies on the underling data store are concurrent access to non-existing saga instances and concurrent access to existing saga instances.

Concurrent access to non-existing saga instances

The persister uses MongoDb's Unique Indexes to ensure only one document can contain the unique data.

Concurrent access to existing saga instances

The persister uses a document versioning scheme built on top of MongoDb's findAndModify command to atomically update the existing persisted data only if it has not been changed since it was retrieved. Since the update is atomic, it will ensure that if there are multiple simultaneous updates to a saga, only one will succeed.

Credits

A major fork of https://github.com/justinsaraceno/NServicebus-Mongo.

Also thanks to @ruslander for his contribution.