Why I am getting cannot determine GraphQL output error? - node.js

Question

I am trying to create simple appliaction with Nest.js, GraphQL and MongoDB. I wnated to use TypeORM and TypeGraphql to generate my schema and make a connection with localhost databasebut but i can not run my server with nest start becouse I am getting this error:
UnhandledPromiseRejectionWarning: Error: Cannot determine GraphQL output type for getArticles
I have no idea why i am getting this error. My class ArticleEntity does't has any not primary types, so there should not be any problem. I tried to remove () => ID from #Field() decorator of filed _id of ArticleEntity class but it didn't helped
ArticleResolver
#Resolver(() => ArticleEntity)
export class ArticlesResolver {
constructor(
private readonly articlesService: ArticlesService) {}
#Query(() => String)
async hello(): Promise<string> {
return 'Hello world';
}
#Query(() => [ArticleEntity])
async getArticles(): Promise<ArticleEntity[]> {
return await this.articlesService.findAll();
}
}
ArticleService
#Injectable()
export class ArticlesService {
constructor(
#InjectRepository(ArticleEntity)
private readonly articleRepository: MongoRepository<ArticleEntity>,
) {}
async findAll(): Promise<ArticleEntity[]> {
return await this.articleRepository.find();
}
}
ArticleEntity
#Entity()
export class ArticleEntity {
#Field(() => ID)
#ObjectIdColumn()
_id: string;
#Field()
#Column()
title: string;
#Field()
#Column()
description: string;
}
ArticleDTO
#InputType()
export class CreateArticleDTO {
#Field()
readonly title: string;
#Field()
readonly description: string;
}
If you need anything else comment

Answer 1

ArticleEntity should be decorated with the #ObjectType decorator as shown in the docs https://typegraphql.com/docs/types-and-fields.html.
#Entity()
#ObjectType()
export class ArticleEntity {
...
}

Answer 2

For anyone who gets this error and uses enums, you may be missing a call to registerEnumType.

Answer 3

In my case, I was using the #ObjectType decorator, but I was importing from type-graphql. I imported from #nestjs/graphql instead, and the problem was resolved.
import { ObjectType } from '#nestjs/graphql';
See here for a related discussion on GitHub.

Answer 4

I was using MongoDB and I had my Query return the schema instead of the model class.
Changing #Query((returns) => UserSchema) to #Query((returns) => User) fixed the issue for me.
user.schema.ts
#ObjectType()
#Schema({ versionKey: `version` })
export class User {
#Field()
_id: string
#Prop({ required: true })
#Field()
email: string
#Prop({ required: true })
password: string
}
export const UserSchema = SchemaFactory.createForClass(User)
user.resolver.ts
#Query((returns) => User)
async user(): Promise<UserDocument> {
const newUser = new this.userModel({
id: ``,
email: `test#test.com`,
password: `abcdefg`,
})
return await newUser.save()
}

Answer 5

Output model class should be decorated with #ObjectType() and then all properties of that class will decorated with #Field().
For any one who is using a custom output model class and NOT an entity(sequelize, typeorm, prisma etc). Because I was using database entity first, everything was working fine till I moved to a more customized output model.
One more case would be someone using class A as output and class B is used within A
export class A{
id: number;
name:string;
childProperty: B
. . . . .
}
export class B{
prop1:string;
prop2:string;
}
In that case class B should also be decorated with #ObjectType and fields (prop1 , prop2 ) should be also be decorated with #Field as well.