It's here! Well, nearly...

Part 2 is available here

I've been eagerly awaiting the release of the Cosmos DB SQL Provider in EF Core. I'm working on a couple of projects at the moment which use ASP.NET Core, Azure Functions, Azure SQL and Cosmos DB - and while using the Document Client directly works very well & is straightforward, I'd rather keep things consistent and use Entity Framework for both SQL and Cosmos DB.

I love the way Microsoft has been moving more of its development into the open. I keep tabs on several repos on Github, including the EF Core one, and I noticed the other day that there had been some activity on the "cosmossqlprovider" branch. And then I saw this...


And then this...


Hmm. Now, I'm pretty rather than waiting for the team to merge, I started to wonder whether I could get this working myself.

So, first step was to clone the repo. I did a quick 'git checkout cosmossqlprovider', made sure everything looked ok, then checked out master again before running 'git merge cosmossqlprovider'. No conflicts, as per the pull request details on Github. Awesome.

It was developed against the 2.2 branch, so I downloaded the 2.2 preview SDK from here. I then ran the EF Core build (as detailed here).

I had to dive into the code a bit to figure out how to get this working in an ASP.NET Core app, and after a bit of work I had it all working...nearly. Unfortunately, every time I tried to save an entity I kept getting a "Method not found" error.

After banging my head against this for a while I thought I'd see if I could get the code working against the current .NET Core version instead.

I created a new solution and copied the EFCore.Cosmos.SQL project into this directory (note - you also need the "src\shared" folder as well).

I then edited the EFCore.Cosmos.SQL.csproj file from this...


to this...

(Note: I had to set the LangVersion to "latest")

And it builds! 2018-08-13-12_04_15-Window-1

Ok, great. So next step is to create a project which uses this. First of all, I created a simple ASP.NET Core Web API project, added a reference to the EFCore.Cosmos.SQL project, and then created an Entities folder with a simple test Entity & DbContext. From poking around in the code I saw that my entities needed a "CollectionName" annotation, and I added this via the Fluent API. I'm just using a collection named 'items', which I already have created.

I ended up with these:





And then hooked it all up in the Startup.cs file as below:


I'd suggest using the Azure Cosmos DB Emulator for local development, available from here.

As a quick test, I'm just editing the ValuesController Get method, adding the following code:

2018-08-13-13_09_27-Window works! Opening up the Data Explorer for the Cosmos DB Emulator shows us the entity, now in document form:


There are a few interesting things here (that took a bit of trial and error to figure out!). Firstly, I needed to define a primary id key, otherwise it throws an error. I used "Id" at first, but it created a document with both "Id" and "id" fields, so I switched to just a lowercase "id" property. Secondly, from what I've seen, JsonProperty annotations don't do anything - so your documents are stored with capitalised properties. Which makes sense, you can now have nice clean POCO entities without having the JsonProperty annotations all over them. Thirdly, there is a "Discriminator" column defined, with the entity name in it. More on that in the next post...

That was a very quick first look - in the next post I'll look at related entities and also give it a try with Azure Functions using the awesome FunctionMonkey library.

Part 2 is available here