How do I generate fragment types for apollo client?

Question

I have an app written with reason-react using apollo-client. I have defined some fragments on the frontend to basically reuse some field definitions. I'm setting up automated tests for a components that uses fragments, but I keep getting this warning saying I need to use the IntrospectionFragmentMatcher.

'You are using the simple (heuristic) fragment matcher, but your queries contain union or interface types. Apollo Client will not be able to accurately map fragments. To make this error go away, use the `IntrospectionFragmentMatcher` as described in the docs: https://www.apollographql.com/docs/react/advanced/fragments.html#fragment-matcher'

I've tried setting up the fragment matcher according to the docs. The codegen result returns no types:

{
  "__schema": {
    "types": []
  }
}

When I queried my server and looked at the manual method recommended by apollo-client, I noticed it would also return no types.

Another strange thing is that when I don't use the fragment matcher, I get the mocked response back but I just get the warnings from apollo. If I do use it then the mocked response doesn't return correctly.

Why would I query the graphql api for fragments defined in my frontend code? Why would I only received these errors when running the tests & using mock data, but not when running my actual application?

Chris B. Chris B. · Accepted Answer · 2019-09-18T23:15:58

As the error states, the default fragment matcher does not work on intersection or union types. You will need to use Apollo's IntrospectionFragmentMatcher. It works by asking the server (introspecting) for information about your schema types, and then providing that information for reference to the cache so that it can match the fields accurately. It's not querying the server for information about the fragments you are defining on the front end, it's asking for data about the GraphQL schema that must be defined on your back end so that it can properly relate the two. There is an example in the documentation, also more information here.

As for why your server is not returning any types, that is a separate issue that would require more info to debug. If you're using Apollo Server, doublecheck your schema to make sure all the necessary types are defined properly and that you are passing them into the server when it's initialized.

How do I generate fragment types for apollo client?

1 Answers