Quick Simple GraphQL Provider On ASP.NET 5.0

Hey guys, my most recent project tackles implementing GraphQL¹ provider using C#. This is my first time implementing this stuff on C#, but I’ve already implemented it before on Java and also on Rust. This are the simple things I’ve learned while implementing a simple (hello world) GraphQL server on C#.

Come on join me and lets dive in! ☄


First of all, you must have a .NET 5.0 SDK (Software Development Kit) installed in your computer and also I assumed you are currently running Windows 10 or Linux with proper environment set.

If you are on Windows 10 and already have a Visual Studio² 2019, just update it to the most recent version, that way would ensure your system to have the latest .NET Core SDK version.

So where do we start?

First we create our ASP.NET³ Web API project on the command-line. Execute the command below to create the project.

This command specifically creates a project with .NET Core 5.0 as target. The --no-https flag specifies we will be only working with non-SSL HTTP server config, and the type of project we generate is web (from an empty ASP.NET core template).

If the command is successful, we should now be able to see the folder GqlNet5Demo. Change directory on to it so we could start our changes to the template project.

Inside the project folder, we need to add now the base core of GraphQL.Net library and its default deserializer. Execute the command in an open shell:

Then this next package is optional only if you need GraphQL Websocket support, specially useful if you are implementing a subscription based GraphQL API. Anyways, for our project lets add this dependency.

Also, add this other package which helps in debugging GraphQL statements on browser. This will install an embedded GraphQL Playground on our demo project, just don’t forget to remove this on a production server.

After all those package installed, lets move on now on to editing our first file. Let’s create the file first named EhloSchema.cs and place it on the root folder. On the file, import the library namespace that we will be using.

After importing the needed libraries, we implement our root query type which will contain the query structure of our GraphQL schema. The query type is useful if you want to only read data.

From the above we also implemented our first query type named “greet” which can be then called like this on the GraphQL playground.

The instruction on creating a GraphQL type starts with Field or AddField following by type of field that will be returned and its required field the name and of course resolver.

If called on the GraphQL playground it would output a JSON with a data message containing “Hello, World”. To be able to run the GraphQL playground, let’s continue on the tutorial.

Still on the file EhloSchema.cs, add this instructions below in order for us to create our first schema. This schema will map the Query to our created class EhloQuery instance.

That’s all for now on the EhloSchema.cs file! This is the most basic requirement needed in order to create a super basic GraphQL server.

Let’s now start modifying the Startup.cs file. Add this new imports which are needed for our constructor.

This two imports allows us to use the IConfiguration and the IWebHostEnvironment abstract interface and their respective allowable methods. The next thing is implement our constructor and class scope variables. See below on what to implement.

After implementing the constructor, we also need to import the GraphQL base library.

Then on the ConfigureServices method we add and build the GraphQL service.

If you look at the instructions above we set and add first our Schema as a singleton class that will be initialize once. Then we set parameters to our GraphQL server, and set its default deserializer. Also, don’t forget we add websocket and dataloader to it. The dataloader is useful to prevent n+1 attacks that happen on GraphQL servers. More information can be found on this link.

We now need to implement calls to respective middlewares and activate the services. First is to activate the websocket protocol on our server, then also enable the GraphQL websocket middleware to inject our schema. The /graphql is the endpoint where the schema will be deployed.

Don’t forget we need to activate also our GraphQL playground so we can use it on our demo GraphQL server. Here’s the full source of our Startup.cs, check whether if you forgot or missed something.

Now its time to run our ASP.NET GraphQL API server. Do that by executing the command on our previous opened shell:

If its all successful, then you should head out to http://localhost:<port>/ui/playground to access the GraphQL Playground. The <port> field pertains to the port indicated in the applicationUrl inside launchSettings.json that can be found inside your project.

If you encounter any problem, just try to re-check all the things we did above or check the full source at bottom of this article.

Our next step is to implement a complex query structure. We first need to implement this classes in our EhloSchema.cs.

This will create two classes which are Message and MessageType. The Message class will be our model class that will store data temporary into our program’s memory. And the MessageType will be the conversion from GraphQL type to our model class which is Message.

After that we need to implement this new field type on our EchoQuery constructor. This a simple example or returning low-complex type query on our server.

Then to test it, we need to access our GraphQL Playground to execute this GraphQL statement.

If everything is okay, it would return a JSON containing no error message and correct response with structure similar to Message data structure.

Next, we move to mutation type. The mutation type is specifically useful if you want to modify data, in CRUD it will be the CUD (Create, Update and Delete). We now need to create the root mutation type, just implement the following class below.

On the constructor, you’ll see we also implemented a field type that will return string and accepts one string argument. We also need to initialize this mutation class that we created on our main schema. Add the line below in the constructor of our EhloSchema class.

After implementing the mutation, build and run the whole project and go to GraphQL Playground to test our mutation. In our case the mutation doesn’t modify any stored data but just return a simple string appended by argument. The mutation statement starts with mutation instead of query.

Next, we implement GraphQL subscription. The subscription on GraphQL is mostly used on events (e.g. someone registered, login notifications, system notifications, etc.) but mostly it can be use on anything that can be streamed.

Let’s implement it now on our EhloSchema.cs file.

Similar to the Query and Mutation, will only implement simple event stream resolver and a subscriber listener. The greetCalled method will just return a simple string upon call on OnNext. Then on EhloSchema constructor same in mutation we also link the root subscription type.

Then we test it on GraphQL Playground. In order to call a subscription type, we start by using the subscription statement.

Here’s the full source code of EhloSchema.cs file. You can re-check all the changes you did before and compare it to this. Also on this source, you’ll find that we also implemented a low-complex method in mutation that will return a structure on mutation. The mutation also accepts custom structure named MessageInputType.

That’s all guys, after checking — build and run the whole project. 🙌


Implementing GraphQL seems a bit daunting at first, but if you know the internals of it you’ll reap many benefits by using it versus normal REST API endpoints. It’s not for this article to discuss the pros and cons of that. Anyways, as you can see its bit easy now to implement GraphQL on C# but I don’t see many enterprise switching over it as it will probably disrupt some of their services.

You can found the complete repository here.

Let me know in the comments if you have questions or queries, you can also DM me directly.

Follow me for similar article, tips, and tricks ❤.

  1. GraphQL is an open-source data query and manipulation language for APIs, and a runtime for fulfilling queries with existing data. GraphQL was developed internally by Facebook in 2012 before being publicly released in 2015. ↩︎
  2. Microsoft Visual Studio is an integrated development environment (IDE) from Microsoft. It is used to develop computer programs, as well as websites, web apps, web services and mobile apps. Visual Studio uses Microsoft software development platforms such as Windows API, Windows Forms, Windows Presentation Foundation, Windows Store and Microsoft Silverlight. It can produce both native code and managed code. ↩︎
  3. ASP.NET is an open-source, server-side web-application framework designed for web development to produce dynamic web pages. It was developed by Microsoft to allow programmers to build dynamic web sites, applications and services. ↩︎

Software Engineer. View my other articles at https://www.vastorigins.com and also guys listen to my podcast about life at https://anchor.fm/vastorigins.

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