Stitching Directive throwing error for array batching

[fahadbillah]

I setup 2 simple gql service and 1 gql gateway to stitch them together using stitching directive. I tried to use array batching to resolve stitched field for efficiency.

Problem is one-to-many relation is throwing error for array batching. After debugging I can see Dataloader throwing error because of value and key length mismatch. Here's the schema.

# Division schema
${stitchingDirectivesTypeDefs}

type Division {
  id: ID
  name: String
  districts: [District]
}

type District {
  id: ID
}

type Query {
  divisions(ids: [ID]): [Division] @merge(
    keyField: "id"
    keyArg: "ids"
  ) 
  _sdl: String!
}

# District schema
${stitchingDirectivesTypeDefs}

type District {
  id: ID
  name: String
  divisionId: ID
  division: Division
}

type Division {
  id: ID
}

type Query {
  districts(ids: [ID]): [District] @merge(
    keyField: "id"
    keyArg: "ids"
  )
  _sdl: String!
}

When I'm running following query (one-to-many) dataloader throwing value & key length mismatch error

query divisions{
  divisions {
    id
    name
    districts {
      id
      name
      divisionId
    }
  }
}

But running inverse query (one-to-one) seems ok by dataloader.

query districts{
  districts {
    id
    name
    division {
      id
      name
    }
  }
}

But it was working fine when I used batchDelegateToSchema instead of stitching directive. Am I missing something? BTW I'm following @gmac stitching handbook. Please suggest me what's wrong with my implementation. Thanks.

[yaacovCR]

Not sure, maybe a repo might help with a minimal reproduction?

Btw I wonder if you need to expose divisionId in your district type as it should be available under division.

[fahadbillah]

Thanks @yaacovCR for quick response. Here's the repo link https://github.com/fahadbillah/stitching-directive
Please run the queries mentioned in readme.

Although I can see districts resolver under divisions query gets triggered and return correct data dataloader unable to map it with keys provided. Mentioning key value length mismatch.

[fahadbillah]

@yaacovCR sorry for bugging you but is it possible to give some feedback on this. thanks.

[yaacovCR]

Sorry didn’t have a chance yet, unfortunately. Note that your resolvers filter based on ids so you don’t return a result per Id, that’s why you are getting an error. I guess its debatable what resolvers should do generally in this case.

But why does the dataloader ask for duplicate ids? Presumably its failing to realize these are the same…. I have to check back…. I wonder if this is a problem only with stitching directives logic rather than the gateway specified code.

[fahadbillah]

I'm trying to achieve following stitching using stitching directive SDL.

stitchSchemas({
  ...
  resolvers: {
    Division: {
      districts: {
        resolve(root, args, context, info) {
          return batchDelegateToSchema({
            schema: districtSchema,
            operation: 'query',
            fieldName: 'districts',
            key: root.id,
            argsFromKeys: (keys) => ({ keys }),
            context,
            info,
          });
        },
      },
    },
  },
})

And getting error from dataloader. To be precise from this line of code -> https://github.com/graphql/dataloader/blob/3e62fbe7d42b7ab1ec54818a1491cb0107dd828a/src/index.js#L330