How can I add additional input arguments at the gateway?

[JonasDoe]

I have an input with two fields:

input CreationInput {
  name: String!
  "This field doesn't exist at the public API, but at the API of the GraphQLService behind the gateway"
  slug: String
}

type Mutation {
  create(input: CreationInput!): MyEntity!
}

The exposed API doesn't come with the slug field, by the GraphQL gateway stitches that for the internal GraphQL microservice with the schema from above. My gateway adds a slug field to the incoming args which get passed to the delegateToSchema call:

...
args['slug'] = 'someSlug'
await delegateToSchema({
 ...
 schema: myRemoteSchemaFromAbove // I've checked, the schema's input type comes with slug
 args: args,
 info: info, // untouched
 ...
})

But this field is ignored, my GraphQL service receives an request where the input just contains the name, and slug being empty.
I figure I could solve this somehow with a Transformer or by modifying the info object like that:

// just a sketch, I wouldn't modify `info` and I would use constants
info.fieldNodes[0].arguments[0].value.fields = info.fieldNodes[0].arguments[0].value.fields.concat({
  kind: 'ObjectField',
  name: { kind: 'Name', value: 'slug' },
  value: { kind: 'StringValue', value: slug }
});

But I wonder whether there's a more straight-forward way.

Thanks for any thoughts on that!

[ardatan]

You can add your additional arguments to args;

args: {
  // your args here
  ...args,
}

Is this what you need? Otherwise please create a reproduction on CodeSandbox or StackBlitz. Thanks!

[JonasDoe]

Thanks for you response! I think I've covered that with the line args['slug'] = 'someSlug'. But it's good to know that it's expected to work this way, so it might be a bug. I'll try to set something up with CodeSandbox and create an issue if I get it done. Might take some time though, since the setup is a bit complex (due to the two schemas) and I'm not really used to CodeSandbox (or the alike).

[JonasDoe]

Yeehaw, I think I managed to set up an example on StackBlitz.

It runs the server and then sends a request to it. In the terminal you can see the query that would go to the remote GraphQL service, with the slug argument missing, so the output looks like

The following query should come with a "slug" argument but doesn't:
         "mutation {\n  create(input: {name: \"someName\"})\n}\n"

[ardatan]

I think I have an issues with Apollo's playground because I couldn't make a query. However your delegateToSchema call is wrong because slug is under input not on top.
You should pass the slug inside the input property;

args: {
  ...args,
  input: {
     ...args.input,
     slug: 'yourSlug'
  }
}

[JonasDoe]

Thank you for the quick response!

• You're right, the playground isn't there, so I send the graphql request automatically with runServer().then(_=>{/*Send request*/}).catch(console.error) to render it unnecessary
• You're right, I set up the arguments the wrong way in the example. Fixed that. (In my real project, I'm modifying args.input, though.)
• I realized that I was wrapping the schemas the wrong way in the example. Fixed that, too.

After all these fixes, it's suddenly working as expected. The query isn't the input string anymore, and there are variables:

query: "mutation ($_v0_input: CreationInput!) {\n  create(input: $_v0_input)\n}\n" 
variables: { _v0_input: { name: 'someName', slug: 'someSlug' } }

So, in theory it's working now as expected, which means: there's something else wrong in my real project. But it's good to know it's not an issue on graphql-tools side and modifying the args is the correct way to go! Thanks for your fast support, I think I can continue from here! :)