"Type ... doesn't have any fields" error on GitHub GraphQL schema.

[Zimmi48]

I am using GitHub's GraphQL API. The following query worked fine with ppx_graphql (the __typename were required though) but it does not work with graphql_ppx_re:

  query issueMilestone($owner: String!, $repo: String!, $number: Int!) {
    repository(owner:$owner, name:$repo) {
      issue(number:$number) {
        id
        milestone { id }
        timelineItems(itemTypes:[CLOSED_EVENT],last:1) {
          totalCount
          nodes {
            __typename
            ... on ClosedEvent {
              closer {
                __typename
                ... on PullRequest {
                  id
                  milestone { id }
                }
                ... on Commit {
                  associatedPullRequests(first: 2) {
                    nodes {
                      id
                      milestone { id }
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }

The error is:

Fatal error: exception Graphql_ppx_base__Schema.Invalid_type("Type IssueTimelineItems doesn't have any fields")

Given that it is GitHub's GraphQL schema, I am pretty confident that this is a valid schema.

Since this error looks specific to the handling of union types, I think it is the same as mhallin/graphql_ppx#74.

Is it a bug or a known limitation? Is there a known workaround? Thanks!

[baransu]

When working with union types you only can query on cases and not on whole field. To adjust your example to graphql_ppx_re you only have to remove __typename from the union field. It's added behind scenes as it allows us to parse the result as one of the provided union cases and wrap it into a poly-variant.

Here is an example of a correct query:

module WorkingQuery = [%graphql
  {|
  query issueMilestone($owner: String!, $repo: String!, $number: Int!) {
    repository(owner:$owner, name:$repo) {
      issue(number:$number) {
        id
        milestone { id }
        timelineItems(itemTypes:[CLOSED_EVENT],last:1) {
          totalCount
          nodes {
            ... on ClosedEvent {
              closer {
                ... on PullRequest {
                  id
                  milestone { id }
                }
                ... on Commit {
                  associatedPullRequests(first: 2) {
                    nodes {
                      id
                      milestone { id }
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }
|}
];

If it doesn't solve your issue please reopen 🙂

[baransu]

@Zimmi48 Added it to the troubleshooting section in README: https://github.com/baransu/graphql_ppx_re#type--doesnt-have-any-fields

[Zimmi48]

Thank you so much for the quick answer! If this hadn't been a migration from ppx_graphql, I would never have manually included this __typename field, and I wouldn't have had any trouble 😆