How to correctly return errors and partial data in list query

[tsteenkamp]

Hi,

so I have a root query that receives a list of IDs of entities and should return details about those or an error if it cannot find the corresponding entity. For example:

@ArgsType()
export class ProductsArgs {
  @Field(() => [Number])
  ids: number[]
}

@ObjectType()
export class Product {
  @Field(() => Number)
  id: number
}

const products = [1, 3].map(id => {
  const product = new Product()
  product.id = id
  return product
})

@Resolver()
export class ProductsResolver {
  @Query(() => [Product])
  async products(@Args() { ids }: ProductsArgs): Promise<Array<Product | GraphQLError>> {
    const list = ids.map(id => products.find(f => f.id === id) || new GraphQLError(`Product ${id} not found`))
    console.log(`list`, list)
    return list
  }
}

If I query now something like:

query {
  products(ids: [1, 2, 3]) {
    id
  }
}

I can see in stdout the expected list of two Products and one GraphQLError, but the graphql response object only contains the errors map, not the valid partial data.

Is there a way to return partial valid data in this case? I'm pretty sure I have seen other / more deeply nested requests, where type-graphql handled partial data and errors as I expected it to do. I was surprised that this was handled as if the error was thrown, altough it is "only" mapped into the result set.

[MichalLytek]

You need to throw the error, not return the error.

const list = ids.map(id => products.find(product => product.id === id));
if (list.some(item => item === undefined)) {
  throw new Error("...");
}

[MichalLytek]

Not possible in GraphQL that single query both resolves data and throw error.

Maybe try to use custom response object type with data and errors properties?

[tsteenkamp]

It is definitely possible. See a minimal example here: https://stackblitz.com/edit/graphql-lxenm4

[MichalLytek]

{
  "errors": [
    {
      "message": "Manufacturer '3' not found.",
      "locations": [
        {
          "line": 2,
          "column": 3
        }
      ],
      "path": [
        "manufacturers",
        1
      ]
    }
  ],
  "data": {
    "manufacturers": [
      {
        "id": "1",
        "name": "Apple"
      },
      null,
      {
        "id": "2",
        "name": "Macmillan"
      }
    ]
  }
}

TypeGraphQL does not add any logic for resolving values, so maybe the problem here is with exposing schema by apollo or something?

[MichalLytek]

 @Query(() => [Product])

 manufacturers(ids: [ID!]!): [Manufacturer]!

Your TypeGraphQL type is not nullable

[tsteenkamp]

Wow, thanks a lot! Stupid mistake.