Leveraging Azure Cosmos DB Partial Document Update With JSON Patch in an ASP.NET Core Web API

A couple of weeks ago the Cosmos DB team has announced support for patching documents. This is quite a useful and long-awaited feature, as up to this point the only way to change the stored document was to completely replace it. This feature opens up new scenarios. For example, if you are providing a Web API on top of Cosmos DB, you can now directly implement support for the PATCH request method. I happen to have a small demo of such Web API, so I've decided to refresh it and play with leveraging this new capability.

Adding PATCH Requests Support to an ASP.NET Core Web API

An important part of handling a PATCH request is deciding on the request body format. The standard approach for that, in the case of JSON-based APIs, is JSON Patch. In fact, Cosmos DB is also using JSON Patch, so it should be easier to leverage it this way.

ASP.NET Core provides support for JSON Patch, but I've decided not to go with it. Why? It's designed around applying operations to an instance of an object and as a result, has internal assumptions about the supported list of operations. In the case of Cosmos DB, the supported operations are different, and that "applying" capability is not needed (it was a great way to implement PATCH when Cosmos DB provided on replace option). I've figured out it will be better to start fresh, with a lightweight model.

public class JsonPatchOperation
{
    [Required]
    public string Op { get; set; }

    [Required]
    public string Path { get; set; }

    public object Value { get; set; }
}

public cla