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Introduction

We all love GraphQL! It's so great and solves many problems that we have with REST API, such as overfetching and underfetching. But developing a GraphQL API in Node.js with TypeScript is sometimes a bit of a pain.

What?

TypeGraphQL is a library that makes this process enjoyable, by defining the schema using only classes and a bit of decorators magic. Example object type:

@ObjectType()
class Recipe {
  @Field()
  title: string;

  @Field(type => [Rate])
  ratings: Rate[];

  @Field({ nullable: true })
  averageRating?: number;
}

It also has a set of useful features, like validation, authorization and dependency injection, which helps develop GraphQL API quickly & easily!

Why?

As I mentioned, developing a GraphQL API in Node.js with TypeScript is sometimes a bit of a pain. Why? Let's take a look at the steps we usually have to make.

First, we create all the schema types in SDL. We also create our data models using ORM classes, which represents our db entities. Then we start to write resolvers for our queries, mutations and fields. This forces us, however, to begin with creating TS interfaces for all arguments and inputs and/or object types. After that, we can actually implement the resolvers, using weird generic signatures, e.g.:

export const recipesResolver: GraphQLFieldResolver<void, Context, RecipesArgs> = async (
  _,
  args,
) => {
  // our business logic, e.g.:
  const repository = getRepository(Recipe);
  return repository.find();
};

The biggest problem is the redundancy in our codebase which makes it difficult to keep things in sync. To add a new field to our entity, we have to jump through all the files: modify entity class, then modify part of the schema, and finally update the interface. The same goes with inputs or arguments: it's easy to forget to update one or make a mistake with the type. Also, what if we've made a typo in field name? The rename feature (F2) won't work correctly.

TypeGraphQL comes to address this issues, based on experience from over a dozen months of developing GraphQL APIs in TypeScript. The main idea is to have only one source of truth by defining the schema using classes and a bit of decorators help. Additional features like dependency injection, validation or auth guards helps with common task that normally we would have to handle by ourselves.