relayStylePagination read method clobbers pageInfo.startCursor and pageInfo.endCursor

[migueloller]

Intended outcome:
With a query as follows:

query {
  someConnectionField {
    edges {
      node {
        id
      }
    }
    pageInfo {
      hasNextPage
      endCursor
    }
  }
}

I would expect endCursor to be the value returned from the API, not "".

Actual outcome:
Even though the API returns a valid cursor in endCursor, the relayStylePagination type policy attempts to read it from edges[0].cursor (or the last edge's cursor) and completely replaces the one in `pageInfo.

These should default to pageInfo.{startCursor,endCursor} and not "".

apollo-client/src/utilities/policies/pagination.ts

Lines 101 to 102 in cefb3c3

	let startCursor = "";
	let endCursor = "";

How to reproduce the issue:
Perform a query as described above while using relayStylePagination.

[meliborn]

Having the same issue, can't use relayStylePagination() at all. Cursors are always empty.

[meliborn]

So i just copied all implementation and replaced

apollo-client/src/utilities/policies/pagination.ts

Lines 101 to 102 in 54fe88a

	let startCursor = "";
	let endCursor = "";

By

let { startCursor } = existing.pageInfo;
let { endCursor } = existing.pageInfo;

[dlqqq]

This is a serious issue. Relay-style pagination is one of the core features offered by all GraphQL implementations, and is included in the official GraphQL docs. Can this please receive further attention?

[benjamn]

@migueloller @diracs-delta @meliborn Please have a look at this PR and let me know if it meets your expectations: #8438

[dlqqq]

@benjamn Gave your PR a quick glance, it looks good to me. Glad it was (relatively) easy! I was just about to submit a PR earlier, but you beat me to it 😅 . TYSM!