Building GraphQL API in .NET Core + HotChocolate + MongoDB + Docker [Part 1]

4 min readMar 28, 2021

In this article, I will demonstrate how to build a GraphQL Web API in .NET Core using the HotChocolate library, MongoDB, and run it in a Docker container. In this first part, we’ll take a look at queries, types, and resolvers. In the next sessions, I will explain how Mutation and Subscription works.

GraphQL Introduction

GraphQL is a query language for APIs and a runtime for fulfilling those queries with your existing data. GraphQL provides a complete and understandable description of the data in your API, gives clients the power to ask for exactly what they need and nothing more, makes it easier to evolve APIs over time, and enables powerful developer tools. See more details here.

Requirements

Visual Studio 2019
Docker
.NET Core knowledge

Installing and running MongoDB on Docker

docker pull mongo
docker run -d -p 27017:27017 --name mongodb mongo

MongoDB basic commands

docker exec -it <CONTAINERID> bash
mongo# show databates & create new one
show dbs
use catalogdb# insert new product
db.Products.save({description: "product description", quantity: 5, price: 15.00})# result
writResult({"nInserted": 1})

Creating a Web API Project

Projects/folders structure

After creating the Web API project, add 2 more Class Library projects (Core and Infrastructure) to manage the repository.

GraphQL.Core

This project needs to install the MongoDB.Bson package, you can find the reference here.

GraphQL.Infrastructure

Everything is fine so far? This project needs to install the MongoDB.Driver package, the reference can be found here.

MongoDbConfiguration is set in the GraphQL.API project under appsettings.json
CatalogContextSeed is executed only once, because the CatalogContext is registered as aSingleton in Startup.cs

At this point, we’ve already set up the Core and Infrastructure projects, so, keep calm and let’s move on to the last part of this first post. 😆

GraphQL.API

This is the part where the magic happens! This project needs to install the HotChocolate and HotChocolate.AspNetCore packages. You can find the references here and here.

Main files and folders

Configurations
Types
Resolvers
Queries
Startup.cs

1. appsettings.json

App and MongoDB configurations.

2. ProductType.cs

Note that we don’t put Category model in the Product model, but, by using ObjectType and overriding the Configure method, it is possible to create a relationship between them. Fantastic, isn't it?

3. CategoryResolver.cs

Used to fetch the Category information by CategoryId from Product (parent).

4. Query.cs

Displays the queries to be consumed.

5. Startup.cs

Done! We have our GraphQL API. Let’s now run the GraphQL.API project and the GraphQL IDE should appear as follows. (Banana Cake Pop)

In the first pane are the available queries, in the middle is where we will create our queries and in the last pane is the result of the queries.

Note that we are calling 2 endpoints at the same request

Dockerizing

1. Dockerfile

2. docker-compose.yml

3. docker-compose.override.yml

4. Running

docker-compose -f docker-componse.yml -f docker-compose.override.yml up -d

Launch the browser and then?

http://localhost:9006/api/graphql

References

Hope you enjoyed this first post, and see you later for Part II.

Thanks a lot for reading.