New Rule: Array bang bang

Many have argued that the default behavior of Arrays in the schema should be [Obj!]!: ex:

type Foo {
  bars: [Baz!]!
}

Most of the time, when you see:

type Foo {
  bars: [Baz]
}

It’s a mistake, because then null and [null, null] are valid values - which is most likely not the cast. Thoughts on a new rule for this?

[n1ru4l]

@goldcaddy77

type Comment {
  id: ID!
  text: String
}

type Post {
  id: ID!
  comments: [Comment!]
}

type Query {
  post(postId: ID!): Post
}

type Mutation {}

Lets say loading the comments of Post failed, by using [Comment!] you can throw an Error in the resolver for your post comments and that will be part of the response. The property comments on the Post will be null. But you still have the partial data for the post.

{
  "data": {
    "post": {
       "id": "1",
       "comments": null,
    }
  },
  "errors": [
     { "something": "...." }
  ]
}

However if you use [Comment!]! and throw an Error in your post comments resolver the post will ne null since it cannot exist without the comments field being an Array.

{
  "data": {
    "post": null
  },
  "errors": [
     { "something": "...." }
  ]
}

You could fix this by returning an empty Array and ignoring the error. However in that case the client that consumes your graphql endpoint will never know there might be some comments and e.g. you cannot hande the UI for retry etc.

I hope this clarifies different use cases

[Caerbannog]

This package by @morris provides a rule that checks for null list items: https://www.npmjs.com/package/graphql-schema-linter-extras It does not check for null lists. Here is the code. ISC license according to package.json.

const {
  ValidationError
} = require("graphql-schema-linter/lib/validation_error");

module.exports = { ListItemsNotNull };

function ListItemsNotNull(context) {
  return {
    ListType(node, key, parent, path, ancestors) {
      if (node.type.kind !== "NonNullType") {
        const ancestorNames = ancestors
          .concat([parent])
          .filter(it => !!it.name)
          .map(it => it.name.value);

        const p = ancestorNames.slice(ancestorNames.length - 2).join(".");

        context.reportError(
          new ValidationError(
            "list-items-not-null",
            `The list field \`${p}\` should not have nullable items.`,
            [node]
          )
        );
      }
    }
  };
}