Dictionary in GraphQL resolver of NestJS

Question

In my NestJS project I’m creating a GraphQL endpoint for a service that returns a dictonary object:

{
 [key: number]: MyDataDto
}

In my .interfaces.ts file I would like to have something like:

interface ArrayAsObject<T> {
  [key: number]: T
}

@ObjectType()
export class MyDataDtoAsDictionary implements ArrayAsObject<MyDataDto> {
  @Field(() => MyDataDto)
  [key: number]: MyDataDto
}

But it gives me an error on the line with @Field

Decorators are not valid here. (ts1206)

If I remove the @Field decorator it throws:

Type MyDataDtoAsDictionary must define one or more fields.

What is the right way to decorate that kind of object for GraphQL resolver?

Did you ever find the answer or did you choose another approach? — Oct 19, 2020 at 23:41
@TheHiggsBroson No, I haven't find any proper solution, so I had to create another service that would return an array of MyDataDto and handle it a bit differently in frontend app. — Oct 20, 2020 at 4:04
Has anyone had the solution, graphql seems not to encourage it: stackoverflow.com/a/41559109/4984888 — Dec 15, 2021 at 9:48

ItchimonjiItchimonji 12 bronze badges · Accepted Answer · 2023-11-20 22:33:18Z

You can use graphql-type-json as response type of a Query in your Resolver.

First of all, you need to install graphql-type-json: https://www.npmjs.com/package/graphql-type-json

npm i graphql-type-json

With this, you can return a Dictionary with a Query like this:

export class EquipmentResolver { 
  private data: { [key: number]: MyDataDto } = {};

  @Query(() => graphqlTypeJson)
  async queryData() {
    return this.data;
  }
}

In a frontend project you can pipe this very easily with RxJS back to a Dictionary:

export class DataComponent {
  private data: { [key: number]: MyDataDto } = {};

  private loadData() {
    this.graphqlService
    .queryData()
    .pipe(
      map((response: { [key: number]: MyDataDto) => {
        this.data = response;
      })
    )
    .subscribe();
  }
}

Dictionary in GraphQL resolver of NestJS