Connection pattern (edges, nodes, pageInfo) in GraphQL

Introduction

The connection pattern helps you get lists of items in small parts, making it easy to load and show data step-by-step.

When showing a list of friends on a social media app, but only a few at a time.

When loading search results page by page to avoid waiting for all results at once.

When displaying messages in a chat app, loading older messages as you scroll up.

When showing products in an online store with many items, loading more as the user scrolls.

When you want to know if there are more items to load after the current list.

Syntax

GraphQL

type Connection {
  edges: [Edge]
  nodes: [Node]
  pageInfo: PageInfo!
}

type Edge {
  cursor: String!
  node: Node
}

type PageInfo {
  hasNextPage: Boolean!
  hasPreviousPage: Boolean!
  startCursor: String
  endCursor: String
}

edges hold the items with cursors to track position.

nodes is a shortcut list of items without cursors.

Examples

This query gets the first 3 users with their cursors and info if more users exist.

GraphQL

query {
  users(first: 3) {
    edges {
      cursor
      node {
        id
        name
      }
    }
    pageInfo {
      hasNextPage
      endCursor
    }
  }
}

This query fetches 5 posts using nodes and checks if there are previous pages.

GraphQL

query {
  posts(first: 5) {
    nodes {
      id
      title
    }
    pageInfo {
      hasPreviousPage
      startCursor
    }
  }
}

Sample Program

This query asks for the first 2 books, their ids and titles, and if there are more books after them.

GraphQL

query {
  books(first: 2) {
    edges {
      cursor
      node {
        id
        title
      }
    }
    pageInfo {
      hasNextPage
      endCursor
    }
  }
}

Important Notes

Use edges when you need the cursor for each item to load more data later.

pageInfo tells you if you can load more items before or after the current list.

nodes is simpler but does not give cursor info for pagination.

Summary

The connection pattern helps load lists in small parts for better performance.

It uses edges with cursors and pageInfo to manage pagination.

You can also use nodes for a simpler list without pagination details.

Practice

1. What is the main purpose of the pageInfo field in the GraphQL connection pattern?

easy

A. To define the schema of the connection

B. To list all the nodes in the connection

C. To provide information about pagination like if there are more pages

D. To store the actual data items

Solution

1. Step 1: Understand the role of pageInfo

   The pageInfo field contains metadata about pagination such as whether there are more pages available.

2. Step 2: Differentiate from edges and nodes

   Unlike edges or nodes which hold data items, pageInfo only provides pagination status.

3. Final Answer:

   To provide information about pagination like if there are more pages -> Option C

4. Quick Check:

   pageInfo = pagination info [OK]

Hint: Remember pageInfo tells if more pages exist [OK]

Common Mistakes:

• Confusing pageInfo with nodes or edges
• Thinking pageInfo holds actual data items
• Ignoring pagination metadata role

2. Which of the following is the correct way to query the edges and node fields in a GraphQL connection?

easy

A. { users { edge { node { id name } } } }

B. { users { nodes { id name } } }

C. { users { pageInfo { hasNextPage } } }

D. { users { edges { node { id name } } } }

Solution

1. Step 1: Recall correct field names in connection pattern

   The connection pattern uses edges (plural) and inside each edge a node (singular) holds the data.

2. Step 2: Check each option's syntax

   { users { edges { node { id name } } } }

   correctly uses edges and node.

   { users { nodes { id name } } }

   uses nodes which is valid but not with edges.

   { users { pageInfo { hasNextPage } } }

   queries only pageInfo.

   { users { edge { node { id name } } } }

   uses edge singular which is incorrect.

3. Final Answer:

   { users { edges { node { id name } } } } -> Option D

4. Quick Check:

   edges plural, node singular inside edges [OK]

Hint: Edges is plural; node is singular inside edges [OK]

Common Mistakes:

• Using 'edge' instead of 'edges'
• Mixing nodes and edges syntax
• Querying pageInfo instead of data fields

3. Given this GraphQL query:

{ posts(first: 2) { edges { cursor node { id title } } pageInfo { hasNextPage } } }

And the server returns two posts with ids 101 and 102, what will pageInfo.hasNextPage be if there are more posts after these two?

medium

A. true

B. false

C. null

D. undefined

Solution

1. Step 1: Understand the meaning of hasNextPage

   hasNextPage is true if more items exist beyond the current page.

2. Step 2: Apply to given scenario

   Since the server returns 2 posts but more posts exist after them, hasNextPage must be true.

3. Final Answer:

   true -> Option A

4. Quick Check:

   More posts after current page means hasNextPage = true [OK]

Hint: More items after current page means hasNextPage true [OK]

Common Mistakes:

• Assuming hasNextPage is false when items equal page size
• Confusing hasNextPage with hasPreviousPage
• Expecting null or undefined instead of boolean

4. You wrote this GraphQL query:

{ comments { edge { node { id text } } } }

But it returns an error. What is the likely cause?

medium

A. The field 'node' should be 'nodes'

B. The field should be 'edges' not 'edge'

C. Missing 'pageInfo' field causes error

D. The query must include 'pageInfo' and 'nodes' together

Solution

1. Step 1: Check the connection field names

   The connection pattern uses edges (plural) not edge (singular).

2. Step 2: Identify the error cause

   Using edge causes a field not found error because the schema expects edges.

3. Final Answer:

   The field should be 'edges' not 'edge' -> Option B

4. Quick Check:

   edges plural required, edge singular causes error [OK]

Hint: Use 'edges' plural, not 'edge' singular [OK]

Common Mistakes:

• Using 'edge' instead of 'edges'
• Thinking 'node' should be plural
• Assuming pageInfo is mandatory for query success

5. You want to fetch a list of products with their IDs and names using the connection pattern. You only need the list of products without pagination info. Which query is best?

hard

A. { products { nodes { id name } } }

B. { products { edges { node { id name } } pageInfo { hasNextPage } } }

C. { products { pageInfo { hasPreviousPage } } }

D. { products { edges { cursor } } }

Solution

1. Step 1: Understand the difference between nodes and edges

   nodes gives a simple list of items without pagination details, while edges includes cursors for pagination.

2. Step 2: Choose the query matching the need

   Since pagination info is not needed, querying nodes directly is simpler and efficient.

3. Final Answer:

   { products { nodes { id name } } } -> Option A

4. Quick Check:

   Use nodes for simple list without pagination [OK]

Hint: Use nodes for simple lists without pagination [OK]

Common Mistakes:

• Using edges and pageInfo when not needed
• Querying only pageInfo without data
• Ignoring simpler nodes field for lists