Everything GraphQL + DotNet Core

Why we need GraphQL?

GraphQL is a query language for APIs which provides a more efficient and flexible alternative to REST. It was originally built by Facebook but it’s open-sourced and is maintained by a large community.

To design web APIs, Restful architecture has become the standard over a couple of years. However, REST APIs have shown to be too inflexible to keep up with the rapidly changing requirements of the clients that access them.

In REST, we generally have multiple endpoints to perform CRUD operations on an entity and also there are overfetching and underfetching problems and it’s return fixed data structures which is a little inflexible in nature. So many times, we need to maintain multiple endpoint for single entity for variations.

This problem is resolved by GraphQL. We can have single API endpoint and for variations can be achieved via changes in query at consumer side. We will understnad this with example going ahead in this article.

Example

We can see from above example, for 'Users' entity, we are having multiple endpoint options.

Similarly, we can see in below code snippet, how query outline is farmed in GraphQL.

type Query {
  books: [Book]
  author(id: ID!): Author
}

type Mutation {
  addBook(title: String!, authorId: ID!): Book
}

type Book {
  id: ID!
  title: String!
  author: Author!
}

type Author {
  id: ID!
  name: String!
  books: [Book]
}

Setting Up GraphQL in DotNet Core

To get started with GraphQL in a DotNet Core application, you’ll need to install the necessary NuGet packages. The primary package is GraphQL, but you might also need GraphQL.Server.Transports.AspNetCore and GraphQL.Server.Ui.Playground for setting up the server and UI.

dotnet add package GraphQL
dotnet add package GraphQL.Server.Transports.AspNetCore
dotnet add package GraphQL.Server.Ui.Playground

Defining the Schema

The schema in GraphQL defines the structure of the API, including the types and their relationships. In DotNet Core, you can define the schema using classes and attributes.

public class BookType : ObjectGraphType<Book>
{
    public BookType()
    {
        Field(x => x.Id).Description("The ID of the book.");
        Field(x => x.Title).Description("The title of the book.");
        Field<AuthorType>("author", "The author of the book.");
    }
}

public class AuthorType : ObjectGraphType<Author>
{
    public AuthorType()
    {
        Field(x => x.Id).Description("The ID of the author.");
        Field(x => x.Name).Description("The name of the author.");
        Field<ListGraphType<BookType>>("books", "The books written by the author.");
    }
}

Implementing Resolvers

Resolvers are functions that handle the logic for fetching data for each field in the schema. In DotNet Core, you can implement resolvers using dependency injection.

public class Query : ObjectGraphType
{
    public Query(IBookRepository bookRepository, IAuthorRepository authorRepository)
    {
        Field<ListGraphType<BookType>>(
            "books",
            resolve: context => bookRepository.GetAllBooks()
        );

        Field<AuthorType>(
            "author",
            arguments: new QueryArguments(new QueryArgument<NonNullGraphType<IdGraphType>> { Name = "id" }),
            resolve: context => authorRepository.GetAuthorById(context.GetArgument<int>("id"))
        );
    }
}

Advanced Features

GraphQL offers several advanced features that can enhance your API:

• Subscriptions: Allow clients to receive real-time updates.

• Caching: Improve performance by caching query results.

• Error Handling: Provide detailed error messages and handle exceptions gracefully.

Testing and Best Practices

Testing your GraphQL API is crucial to ensure its reliability. Use tools like GraphQL Playground for manual testing and libraries like GraphQL.Client for automated tests. Follow best practices such as:

• Schema Design: Keep your schema intuitive and well-documented.

• Security: Implement proper authentication and authorization.

• Performance: Optimize queries and use batching to reduce load.

Conclusion

Integrating GraphQL with DotNet Core can significantly improve the flexibility and efficiency of your APIs. By leveraging GraphQL’s powerful features and following best practices, you can build robust and scalable APIs that meet the evolving needs of your clients.

This article explores the advantages of using GraphQL over REST for building APIs, highlighting its flexibility, efficiency, and client-driven approach. It discusses integrating GraphQL with DotNet Core, detailing setup, schema definition, and resolver implementation. The article also covers advanced features like subscriptions, caching, and error handling, along with testing strategies and best practices for a robust GraphQL API. Real-world examples and case studies illustrate successful implementations, and the conclusion emphasizes the future potential of GraphQL in the DotNet Core ecosystem.