Schema Generator cannot determine GraphQL output type for custom object within DTO

Question

Coming from a laravel background I try to get into node.js/graphQL/MongoDB and stumbled over nest.js framework which looks pretty nice. So I tried to set up a simple GraphQL API for testing and understanding how it all works. Therefore I created a mongoose Schema for a user as well as a model ( type-graphql ) and a DTO for creating such a user via mutation.

This works pretty fine but then I wanted to add a nested object called settings within the user to try how this would work and I simply don't get it and also don't find any nest.js or type-graphql specific examples for such an implementation. Is this simply not feasible using the "code first" approach of nest.js ? Because the schema generator always gives me an error while compilation saying :

"UnhandledPromiseRejectionWarning: Error: Cannot determine GraphQL output type for settings".

user.model.ts

import { Field, ID, ObjectType } from 'type-graphql'
import UserSettingsType from './user.settings.type'

@ObjectType()
export class User {
  @Field((type) => ID)
  id: string

  @Field()
  email: string

  @Field((type) => UserSettingsType)
  settings: {}
}

user.settings.type.ts

import { Field, ObjectType } from 'type-graphql'

@ObjectType()
export class UserSettings {
  @Field()
  theme: string

  @Field()
  description?: string

  @Field((type) => [String])
  visited: string[]
}

new-user.input.ts

import { IsOptional, IsEmail, IsBoolean, Length, MaxLength, IsArray } from 'class-validator'
import { Field, InputType } from 'type-graphql'
import UserSettingsType from '../graphql/user.settings.type'

@InputType()
export class NewUserInput {
  @Field()
  @IsEmail()
  email: string

  @Field((type) => UserSettingsType)
  @IsOptional()
  @IsArray()
  settings: {}
}

As you can see I defined a new type UserSettings in a separate file (following the best practices of nest.js ) and allocated it as a type within the User model as well as the new-user DTO class. The error is thrown for the DTO class (NOT for the model) and if I change it there to something like [String] instead of UserSettingsType it is compiling.

I'm not sure if you need the resolver or the service/mongoose logic for this actual problem if so I can also post that of course!

Answer 1

Had similar issue migrating from express to nestjs.

After reading the docs realised that problem isn't the nested objects, but wrong imports.

You should use @nestjs/graphql imports instead of type-graphql .

EG

// changes this
import { Field, ID, ObjectType } from 'type-graphql'
// to
import { Field, ID, ObjectType } from '@nestjs/graphql'

Same applies to any other import from type-graphql

Answer 2

I had the same problem, solved it with the nest Documentation, you have to make scalar types, this was posted a long ago but hey, hope this helps someone.

When your scalar's done, declare your field this way:

@Field((type) => UserSettingsType)
settings: SettingsScalar (replace by however you call your new type)

Add [] at the end of SettingsScalar if it's an array of objects.

https://docs.nestjs.com/graphql/scalars

Also don't hesitate to delete your dist repository and schema.gql, build your app and run it, don't know why but nothing seemed to change in my schema before I did that.