Cursor-based pagination in GraphQL - Mini Project: Build & Apply

Cursor-based Pagination in GraphQL

📖 Scenario: You are building a GraphQL API for a blog platform. The blog has many posts, and you want to show posts to users in small chunks (pages) instead of all at once. This helps the app load faster and makes it easier for users to browse posts.

🎯 Goal: Create a GraphQL query that implements cursor-based pagination to fetch blog posts in pages. You will set up the data structure, add a pagination configuration, write the main query logic using cursors, and complete the pagination response structure.

📋 What You'll Learn

Create a list of posts with exact titles and IDs

Add a variable for the page size limit

Write a GraphQL query that fetches posts after a given cursor

Complete the pagination response with edges, nodes, and pageInfo

💡 Why This Matters

🌍 Real World

Cursor-based pagination is used in many apps to efficiently load data in chunks, improving user experience and reducing server load.

💼 Career

Understanding cursor-based pagination is important for backend developers working with APIs, especially GraphQL, to build scalable and performant data fetching.

1

Create the posts data list

Create a list called posts with these exact entries: { id: "1", title: "GraphQL Basics" }, { id: "2", title: "Advanced GraphQL" }, { id: "3", title: "GraphQL Pagination" }, { id: "4", title: "GraphQL Subscriptions" }, { id: "5", title: "GraphQL Security" }.

GraphQL

# Your code here

Hint

Use a list of objects with id and title keys exactly as shown.

2

Add the page size limit variable

Add a variable called pageSize and set it to 2 to limit the number of posts returned per page.

GraphQL

posts = [
  { id: "1", title: "GraphQL Basics" },
  { id: "2", title: "Advanced GraphQL" },
  { id: "3", title: "GraphQL Pagination" },
  { id: "4", title: "GraphQL Subscriptions" },
  { id: "5", title: "GraphQL Security" }
]
# Your code here

Hint

Set pageSize to 2 to fetch two posts per page.

3

Write the GraphQL query with cursor logic

Write a GraphQL query called getPosts that takes an optional after cursor argument of type ID. Use posts and pageSize to return posts after the cursor, limited by pageSize. Use edges with cursor and node fields.

GraphQL

posts = [
  { id: "1", title: "GraphQL Basics" },
  { id: "2", title: "Advanced GraphQL" },
  { id: "3", title: "GraphQL Pagination" },
  { id: "4", title: "GraphQL Subscriptions" },
  { id: "5", title: "GraphQL Security" }
]

pageSize = 2

# Your code here

Hint

Use edges with cursor and node fields inside the query.

4

Complete the pagination response with pageInfo

Add the pageInfo field inside the posts query response. Include hasNextPage and endCursor fields to complete the cursor-based pagination structure.

GraphQL

posts = [
  { id: "1", title: "GraphQL Basics" },
  { id: "2", title: "Advanced GraphQL" },
  { id: "3", title: "GraphQL Pagination" },
  { id: "4", title: "GraphQL Subscriptions" },
  { id: "5", title: "GraphQL Security" }
]

pageSize = 2

query getPosts($after: ID) {
  posts(after: $after, first: pageSize) {
    edges {
      cursor
      node {
        id
        title
      }
    }
    # Your code here
  }
}

Hint

Include pageInfo with hasNextPage and endCursor inside the posts field.

Practice

1. What is the main purpose of cursor-based pagination in GraphQL?

easy

A. To fetch all data at once without limits

B. To sort data alphabetically

C. To fetch data in small parts using a cursor to mark position

D. To delete data from the database

Solution

1. Step 1: Understand pagination purpose

   Pagination is used to split large data into smaller parts for easier handling.

2. Step 2: Identify cursor role

   Cursor marks the position in the data to fetch the next part without overlap or missing items.

3. Final Answer:

   To fetch data in small parts using a cursor to mark position -> Option C

4. Quick Check:

   Cursor-based pagination = fetch data in parts [OK]

Hint: Cursor marks position to fetch next data chunk [OK]

Common Mistakes:

• Thinking pagination fetches all data at once
• Confusing cursor with sorting
• Assuming pagination deletes data

2. Which of the following is the correct way to request the first 5 items after a cursor in GraphQL?

easy

A. { items(fetch: 5, cursor: "cursor123") { edges { node } } }

B. { items(limit: 5, startAfter: "cursor123") { edges { node } } }

C. { items(take: 5, afterCursor: "cursor123") { edges { node } } }

D. { items(first: 5, after: "cursor123") { edges { node } } }

Solution

1. Step 1: Recall GraphQL cursor pagination syntax

   The standard uses first to limit items and after to specify the cursor.

2. Step 2: Match options with correct syntax

   { items(first: 5, after: "cursor123") { edges { node } } } uses first and after correctly; others use incorrect argument names.

3. Final Answer:

   { items(first: 5, after: "cursor123") { edges { node } } } -> Option D

4. Quick Check:

   Use first and after arguments [OK]

Hint: Use first and after arguments for cursor pagination [OK]

Common Mistakes:

• Using limit instead of first
• Using startAfter or afterCursor which are invalid
• Confusing argument names

3. Given this GraphQL query:
{ users(first: 3, after: "YXJyYXljb25uZWN0aW9uOjE=") { edges { node { id name } } pageInfo { hasNextPage endCursor } } }
What does the endCursor represent in the result?

medium

A. The cursor of the last item in the current page

B. The total number of items in the database

C. The cursor of the first item in the current page

D. The number of pages available

Solution

1. Step 1: Understand pageInfo fields

   endCursor marks the cursor of the last item returned in the current page.

2. Step 2: Differentiate from other fields

   hasNextPage shows if more pages exist; endCursor is not a count or first item cursor.

3. Final Answer:

   The cursor of the last item in the current page -> Option A

4. Quick Check:

   endCursor = last item cursor [OK]

Hint: endCursor points to last item fetched [OK]

Common Mistakes:

• Confusing endCursor with total count
• Thinking endCursor is first item cursor
• Assuming endCursor is page count

4. You wrote this GraphQL query for cursor pagination:
{ posts(first: 10, afterCursor: "abc123") { edges { node { title } } } }
Why does this query fail?

medium

A. The argument should be named after, not afterCursor

B. The first argument must be a string, not a number

C. The edges field is invalid in cursor pagination

D. The cursor value cannot be a string

Solution

1. Step 1: Check argument names for cursor pagination

   The correct argument to specify the cursor is after, not afterCursor.

2. Step 2: Validate other parts

   first accepts a number; edges is valid; cursor values are strings.

3. Final Answer:

   The argument should be named after, not afterCursor -> Option A

4. Quick Check:

   Use 'after' argument name [OK]

Hint: Use 'after' not 'afterCursor' for cursor argument [OK]

Common Mistakes:

• Using incorrect argument names
• Thinking first must be string
• Misunderstanding edges field usage

5. You want to fetch all comments in batches of 4 using cursor-based pagination. The first query is:
{ comments(first: 4) { edges { node { id text } } pageInfo { hasNextPage endCursor } } }
To fetch the next batch, which query should you use?

hard

A. { comments(limit: 4, after: "endCursor_value") { edges { node { id text } } } }

B. { comments(first: 4, after: "endCursor_value") { edges { node { id text } } pageInfo { hasNextPage endCursor } } }

C. { comments(last: 4, after: "endCursor_value") { edges { node { id text } } } }

D. { comments(first: 4, before: "endCursor_value") { edges { node { id text } } } }

Solution

1. Step 1: Understand how to continue pagination

   Use the after argument with the endCursor value from the previous page to fetch the next batch.

2. Step 2: Check argument correctness

   first: 4 limits to 4 items; after moves cursor forward; before or last are for backward pagination.

3. Final Answer:

   { comments(first: 4, after: "endCursor_value") { edges { node { id text } } pageInfo { hasNextPage endCursor } } } -> Option B

4. Quick Check:

   Use first and after with endCursor for next batch [OK]

Hint: Use first and after with endCursor to paginate forward [OK]

Common Mistakes:

• Using before instead of after for next page
• Using last instead of first for forward pagination
• Using limit instead of first argument