Unit of work in mongodb and C#

Question

I know that MongoDB is not supposed to support unit of work, etc. But I think it would be nice to implement the repository which would store only the intentions (similar to crit

Answer 1

While researching design patterns, I was creating a basic repository pattern for .Net Core and MongoDB. While reading over the MongoDB documentation I came across an article about transactions in MongoDB. In the article it specified that:

Starting in version 4.0, MongoDB provides the ability to perform multi-document transactions against replica sets.

Looking around the intertubes I came across a library that does a really good job of implementing the Unit of Work pattern for MongoDB.

Answer 2

If you are interested in an implementation similar to Rob Connery's and NBlog storage code but using the mongodb csharp driver 2.0 (that is asynchronous), you can look at:

https://github.com/alexandre-spieser/mongodb-generic-repository

You can then write a custom repository inheriting from BaseMongoRepository.

public interface ITestRepository : IBaseMongoRepository
{
    void DropTestCollection<TDocument>();
    void DropTestCollection<TDocument>(string partitionKey);
}

public class TestRepository : BaseMongoRepository, ITestRepository
{
    public TestRepository(string connectionString, string databaseName) : base(connectionString, databaseName)
    {
    }

    public void DropTestCollection<TDocument>()
    {
        MongoDbContext.DropCollection<TDocument>();
    }

    public void DropTestCollection<TDocument>(string partitionKey)
    {
        MongoDbContext.DropCollection<TDocument>(partitionKey);
    }
}

Answer 3

Don't worry too much about opening and closing connections. The MongoDB C# driver maintains an internal connection pool, so you won't suffer overheads of opening and closing actual connections each time you create a new MongoServer object.

You can create a repository interface that exposes your data logic, and build a MongoDB implementation that is injected where it's needed. That way, the MongoDB specific connection code is abstratced away from your application, which only sees the IRepository.

Be careful trying to implement a unit-of-work type pattern with MongoDB. Unlike SQL Server, you can't enlist multiple queries in a transaction that can be rolled back if one fails.

For a simple example of a repository pattern that has MongoDB, SQL Server and JSON implementations, check out the NBlog storage code. It uses Autofac IoC to inject concrete repositories into an ASP.NET MVC app.