Support for pagination when using relay pattern

[netixx]

Describe the solution you'd like
i would like the generated file to expose a function such as:

func queryPaged(
	ctx context.Context,
	client graphql.Client,
	pageSize int,
	pf func(T) error,
) error {
	var cursor *string
	resp, err := query(ctx, client, pageSize, cursor)
	if err != nil {
		return nil
	}

	for _, edge := range resp.X.Edges {
		if err := pf(edge.GetNode()); err != nil {
			return err
		}
	}
	return nil
}

The issue I have is that this needs to be generated as the "X" is the query endpoint so it's not fixed.
One possibility is to add a generic method to the root query that returns the node inside "data",
Then we can write a generic pager with interfaces and generics.

Describe alternatives you've considered
Writing a pager function for every query, but that sort of defeats the purpose of the generator.

Additional context
The relay connection paging pattern is described here: https://relay.dev/graphql/connections.htm and here: https://graphql.org/learn/pagination/.

[benjaminjkraft]

Definitely agree this would be useful, I think the question is just what exactly to add! Would love to hear a bit more from you and any other interested users a description of what you're trying to do so we can try to optimize for it.

[netixx]

I would like the generator to make some code that enables me to transparently use API where a pager is available.

Right now I need to write an additional bit of code for every request I write, to handle the paging mecanism (iterating through all the pages until the end), it looks a little bit like the function in the description, and it mostly the same for each query (only the X differs), so it seems like an good opportunity to have it generated.

The query looks like that:

query Endpoint($pageSize: Int!, $cursor: Cursor) {
  endpoint(first: $pageSize, after: $cursor) {
    pageInfo {
      hasNextPage
      endCursor
    }
    edges {
      node {
        id
        name
...
      }
    }
  }
}

I have thought some more about that, and I am not sure how/if the following points can be handled:

• the paging info needs to be specified in the query (both return values and parameters). Either the generator adds those automatically, or maybe it can detect in the query that there is going to be a paging api involved ?
• this can only work with a well defined/known paging API (it probably is harder to support any custom paging scheme)
• if a query uses multiple endpoints, how to handle the combined paging ? Iter until all cursors/hasNextPage are finished ?

[benjaminjkraft]

Yeah, agreed. I think (hope?) relay is concrete enough that as long as you follow it that's enough for us to generate. But I'm not sure the right API to expose. It might be helpful to look at other paginated APIs in Go and see how they do it -- I guess probably these days the answer is you have an iter of pages, and a util to flatten it to a single page, or something?

Anyway, if we can define a desired API, I think this would be a fun way to play with #237.