CODEWITHSUNDEEP
graphql
Rico Kahler
Rico Kahler

Reputation: 19242

What's the difference between top-level edges and top-level nodes?

I'm new to GraphQL and I'm using WPGraphQL and WooGraphQL.

Their top level connections allow me to expand both nodes and edges like so:

{
  wpgraphql {
    productCategories {
      # What's the difference between these?

      # 1) top-level nodes
      nodes {
        id
        name
      }

      # 2) top-level edges
      edges {
        node {
          id
          name
        }
      }
    }
  }
}

Which returns a response like so (IDs omitted):

{
  "data": {
    "wpgraphql": {
      "productCategories": {
        "nodes": [
          {
            "name": "Accessories"
          },
          {
            "name": "Gift Cards"
          },
          {
            "name": "Indoor"
          }
        ],
        "edges": [
          {
            "node": {
              "name": "Accessories"
            }
          },
          {
            "node": {
              "name": "Gift Cards"
            }
          },
          {
            "node": {
              "name": "Indoor"
            }
          }
        ]
      }
    }
  }
}

My question is simply: Which one do I use? Why are there both?

Here is a screenshot of the GraphiQL explorer if that helps.

explorer preview

Upvotes: 1

Views: 814

Answers (1)

Daniel Rearden
Daniel Rearden

Reputation: 84697

GraphQL schemas that implement the Relay specification utilize Connection types to model one-to-many or many-to-many relationships.

Each connection includes a list of edges and a PageInfo object. Each edge includes a node and the cursor for that node.

Edges may also contain additional fields -- for example, if we have a friends connection between User nodes, we might include the timestamps when the friendships were created. Normally, though, edges are only used for the cursor field they expose. The cursor value is used when paginating through the connection and exposing it for every edge means you can start your pagination from any arbitrary point in the results. The cursor is not included as part of the node because it's may be specific to the connection and not just the node itself (for example, some cursors encode sort criteria).

However, if as a client you don't need to paginate the results of a connection and just want to fetch all the nodes, you probably don't care about cursors. In these scenarios, having edges doesn't add any value and just increases the depth of your query. As a result, as a convenience to the client, some GraphQL services have opted to exposing just the nodes for the connection in addition to the edges.

Upvotes: 4

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