Getting Unsupported token `on` [GraphQL]

Question

Issue: We goto 'on' in the query, while build apollo is complaining about the on keyword in the query (*.graphql)

GraphQL query:

query TimeLine($inputData: InputData!) {
    getTimeLine(inputData: $inputData) {
        on
        updated
 }
}

Error: Unsupported token on (com.apollographql.apollo.compiler.parser.GraphQLDocumentParseException).

Env: Kotlin, apolloGraphQLVersion: "1.3.2"

Answer 1

This happens because the on keyword is a reserved keyword in GraphQL.

One of the Type Conditions is on NamedType, see the official spec file of GraphQL.

query FragmentTyping {
  profiles(handles: ["zuck", "cocacola"]) {
    handle
    ...userFragment
    ...pageFragment
  }
}

fragment userFragment on User {
  friends {
    count
  }
}

fragment pageFragment on Page {
  likers {
    count
  }
}

See the on used in fragment userFragment on User? Your GraphQL got confused because you are using on as a field within the query, while it expects to be a fragment. Read more about fragments here. Also, a fragment's name can be anything, except for on, see the official spec file.

One way to solve this issue might be to rename the field in your query, but I am not sure if GraphQL will complain about this approach as well:

query TimeLine($inputData: InputData!) {
    getTimeLine(inputData: $inputData) {
        dataOn: on
        updated
 }
}