Dataloader Problem

Problem.md

(See example query below)

Sequence of HTTP requests (with naive dataloader usage):

1. Fetch a page of article IDs

   /article-ids/?first=10

2. Batch fetch the articles represented by each ID

   /articles/batch/{id1,id2,...id10}/

3. For each article, fetch a page of comment IDs

   /articles/{n}/comment-ids/?first=3 (repeats 10 times)

4. Fetch each comment batch, fetch the comments (can't be batched because previous steps won't complete at the same time)

   /comments/batch/{id1,id2,id3}/ (repeats 10 times)

Total number of request: 22

Now with more sophisticated dataloader usage:

1. Fetch a page of article IDs

   /article-ids/?first=10

2. Batch fetch the articles represented by each ID

   /articles/batch/{1,2,...n}/

3. Batch fetch pages of 3 comment IDs for each article

   /articles/{n}/comment-ids/batch/?first=3

4. Fetch all the comments for all page batches.

   /comments/batch/{1,2,...30}/

Total number of requests: 4

Why is the second way harder? Dataloader assumes the only necessary information for constructing a batch request is the list of IDs. When dealing with graph nodes this is correct. But when dealing with edges we need more information, specifically page size.

Query.graphql

{
  viewer {
    articles(first: 10) {
      edges {
        node {
          title
          slug
          body
          comments(first: 3) {
            edges {
              node {
                email
                body  
              }
            }
          }
        }
      }
    }
  }
}