Hi, I have the following schema:

# Comment
# - Schema
type Comment @model {
  # Generated by server
  id: ID! @isUnique
  createdAt: DateTime!
  updatedAt: DateTime!

  # Data
  text: String!
  # - Relations
  parent: Comment @relation(name: "CommentOnComment")
  children: [Comment!]! @relation(name: "CommentOnComment")
  author: User! @relation(name: "UserOnComment")
  post: Post! @relation(name: "PostOnComment")
  votes: [CommentVote!]! @relation(name: "CommentOnCommentVote")
}

And the following permission query on

Comment.create

(inspired by https://docs-next.graph.cool/guides/auth/authorization-for-a-cms-miesho4goo#editors-can-only-assign-themselves-as-the-document-owner):

query isUser($user_id: ID!, $authorUser_id: ID!) {
  SomeUserExists(filter: {
    AND: [
      { id: $user_id },
      { id: $authorUser_id }
    ]
  })
}

When running the following query (with the right auth token):

mutation create {
  createComment(
    text: "Waow, amazing",
    authorId: "cj8tal6jg0pxv0192epmhlaha",
    postId: "cj8vshelb01x601742ff1c0tt",
  ) {
    id
  }
}

I have the following error:

Permission Query is invalid. Could not be executed. Error Message: Error during variable coercion. Violations:\n\nVariable '$authorUser_id' expected value of type 'ID!' but value is undefined. Reason: Expected non-null value, found null. (line 1, column 29):\nquery isUser($user_id: ID!, $authorUser_id: ID!) {\n                            ^

Am I doing something wrong here?

Your permission query is incorrect I think.

Yes, the authenticated user should be able to create comments for himself only

Something like this should work:

{
    SomeUserExists(
      filter: {
        id: $user_id
        comments_some: { id: $node_id }
      }
    )
  }

Hmm the docs say:

For all write operations, all matching permission queries are executed and evaluated before the pending operation

The user doesn't have the comment yet when I'm creating it