troubleshooting
"Type ... doesn't have any fields"
Sometimes when working with union types you'll get the following error.
Fatal error: exception Graphql_ppx_base__Schema.Invalid_type("Type IssueTimelineItems doesn't have any fields")
This is an example of a query that will result in such error:
nodes {
__typename
... on ClosedEvent {
closer {
__typename
... on PullRequest {
id
milestone { id }
}
}
}
}
This is because we allow querying union fields only in certain cases. GraphQL
provides the __typename field but it's not present in GraphQL introspection
query thus graphql-ppx doesn't know that this field exists. To fix your query
simply remove __typename. It's added behinds a scene as an implementation
detail and serves us as a way to decide which case to select when parsing your
query result.
This is an example of a correct query:
nodes {
... on ClosedEvent {
closer {
... on PullRequest {
id
milestone { id }
}
}
}
}