Pagination

Mix.install([
  {:github_graphql_smartcell, "~> 0.1.0"}
])

GraphQL Pagination

While GraphQL has a pretty good pagination story it is still GraphQL which means the query itself needs to know about the pagination data and variables.

Here’s a query that will get the database IDs for your first 10 followers

{
  viewer {
    followers(first: 10) {
      nodes {
        databaseId
      }
    }
  }
}

Great right? But how do you paginate?

Well, you need to ask for pageInfo with endCursor and hasNextPage

{
  viewer {
    followers(first: 10) {
      pageInfo {
        endCursor
        hasNextPage
      }
      nodes {
        databaseId
      }
    }
  }
}

But that’s not enough of course. If you execute this query in your GitHub GraphQL smart cell you should see a message

endCursor is not advancing: halting queries

That’s because the GraphQL query depends on variables for pagination. And variables must be declared and known to both the querying code AND the query itself.

{
  viewer {
    followers(first: $first, after: $after) {
      pageInfo {
        endCursor
        hasNextPage
      }
      nodes {
        databaseId
      }
    }
  }
}

Because the smart cell is the querying code we unfortunately have to simply agree to use well-known names for $first and $after. We could make the smart cell have extra inputs to declare the variables and then declare the names of the variables but that seems even more confusing.

Also that’s STILL not enough to make GraphQL happy. You need to declare the names and types of the variables too!

That means you need to explicitly add the normally optional query {} wrapper and declare the variables and their types.

query($first: Int, $after: String) {
  viewer {
    followers(first: $first, after: $after) {
      pageInfo {
        endCursor
        hasNextPage
      }
      nodes {
        databaseId
      }
    }
  }
}

Then, at last, if you execute that query in the GitHub GraphQL smart cell you should see a list of all of your followers’ databaseIds.

Please clap because pulling out the pageInfo and nodes in a mostly generic way was a pain.

But also watch out because I probably did not account for some shapes of query results and things will blow up.

But for at least the simple queries I’ve executed so far this smart cell

• Understands how to simply return results if the query does not declare pagination
• Understands how to recognize if there’s pagination info but not usage in the query and return the results without endlessly querying the same cursor.
• Understands how to paginate nodes with pageInfo data into a combined list