Relay specification compliance in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this Relay-compliant GraphQL query?

Given a GraphQL schema with a Node interface and a User type implementing it, what will be the output of this query fetching a user by ID with Relay's node field?

GraphQL

query {
  node(id: "VXNlcjox") {
    id
    ... on User {
      name
    }
  }
}

A { "data": { "node": { "id": "VXNlcjox", "name": "Alice" } } }

B { "data": { "node": { "id": "1", "name": "Alice" } } }

C { "data": { "node": null } }

D { "errors": [{ "message": "Field 'node' does not exist" }] }

💡 Hint

Remember that Relay encodes the global ID as a base64 string combining type and ID.

Relay uses a global ID encoded as base64 combining the type and the internal ID. Here, "VXNlcjox" decodes to "User:1", so the node field returns the user with id "VXNlcjox" and name "Alice".

🧠 Conceptual

intermediate

Which Relay specification rule ensures consistent pagination?

Which of the following Relay specification rules is responsible for consistent pagination behavior across different GraphQL connections?

A Queries must use fragments for all fields.

B Every node must have a globally unique <code>id</code> field.

C All connections must implement <code>edges</code> and <code>pageInfo</code> fields.

D Mutations must return a <code>clientMutationId</code>.

💡 Hint

Think about how Relay handles lists and pagination.

Relay requires connections to have edges (list of items with cursors) and pageInfo (pagination info) fields to standardize pagination.

📝 Syntax

advanced

Which GraphQL fragment correctly implements Relay's Node interface?

Select the fragment that correctly queries a Relay Node with its global ID and typename.

GraphQL

fragment NodeFragment on Node {
  id
  __typename
}

A fragment NodeFragment on Node { id __type }

B fragment NodeFragment on Node { id name }

C fragment NodeFragment on Node { __id __typename }

D fragment NodeFragment on Node { id __typename }

💡 Hint

Relay nodes always have an id and __typename.

The Relay Node interface requires the id field and __typename to identify the type. Option D correctly includes both.

❓ optimization

advanced

How to optimize Relay pagination queries to reduce overfetching?

Which approach best optimizes Relay pagination queries to avoid fetching unnecessary data?

A Always fetch all edges without limits to avoid multiple queries.

B Use <code>first</code> or <code>last</code> arguments with a small number and request only needed fields in <code>edges.node</code>.

C Include all possible fields in the <code>node</code> selection to prevent future queries.

D Avoid using <code>pageInfo</code> to reduce query size.

💡 Hint

Think about limiting data and selecting only what you need.

Using first or last limits the number of items fetched, and selecting only necessary fields reduces data size, optimizing performance.

🔧 Debug

expert

Why does this Relay mutation response cause a client error?

A Relay mutation returns this response: { "data": { "updateUser": { "user": { "id": "1", "name": "Bob" } } } } Why does Relay client report an error?

A The <code>id</code> field is not a global ID encoded as base64.

B The mutation response is missing <code>clientMutationId</code>.

C The <code>user</code> field should be named <code>node</code>.

D The response is missing the <code>edges</code> field.

💡 Hint

Relay expects global IDs in mutation responses.

Relay requires all id fields to be globally unique base64-encoded strings. Here, "1" is not encoded, causing client errors.

Practice

1. What is the main purpose of the edges field in a Relay-compliant GraphQL connection?

easy

A. To store metadata about the entire list

B. To hold the list of items along with their cursors for pagination

C. To define the total count of items in the list

D. To specify the GraphQL schema version

Solution

1. Step 1: Understand Relay connection structure

   Relay connections use edges to represent each item with its cursor for pagination.

2. Step 2: Identify the role of edges

   The edges field contains nodes (items) and cursors, enabling smooth pagination.

3. Final Answer:

   To hold the list of items along with their cursors for pagination -> Option B

4. Quick Check:

   edges = items + cursors [OK]

Hint: Edges always pair items with cursors for pagination [OK]

Common Mistakes:

• Confusing edges with pageInfo
• Thinking edges store only items without cursors
• Mixing edges with totalCount field

2. Which of the following is the correct syntax to request the first 5 items in a Relay connection named users?

easy

A. { users(first: 5) { edges { node { id } } } }

B. { users(limit: 5) { edges { node { id } } } }

C. { users(count: 5) { edges { node { id } } } }

D. { users(take: 5) { edges { node { id } } } }

Solution

1. Step 1: Recall Relay pagination argument

   Relay uses first to specify how many items to fetch from the start.

2. Step 2: Check syntax correctness

   Only first: 5 is valid; limit, count, and take are not Relay standard arguments.

3. Final Answer:

   { users(first: 5) { edges { node { id } } } } -> Option A

4. Quick Check:

   Use first for Relay pagination [OK]

Hint: Use 'first' to fetch initial items in Relay queries [OK]

Common Mistakes:

• Using non-Relay arguments like limit or count
• Omitting edges or node fields
• Confusing Relay with REST query parameters

3. Given this GraphQL query on a Relay connection:

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

And the server returns:

{ "data": { "posts": { "edges": [ { "cursor": "cursor1", "node": { "title": "Post A" } }, { "cursor": "cursor2", "node": { "title": "Post B" } } ], "pageInfo": { "hasNextPage": true } } } }

What does hasNextPage indicate?

medium

A. The query failed to fetch posts

B. There are no more posts after the current 2

C. The current page is the last page

D. There are more posts available after the current 2

Solution

1. Step 1: Understand pageInfo.hasNextPage

   This field tells if more items exist beyond the current page.

2. Step 2: Interpret the returned value

   The value true means more posts exist after the fetched two.

3. Final Answer:

   There are more posts available after the current 2 -> Option D

4. Quick Check:

   hasNextPage = true means more data [OK]

Hint: True hasNextPage means more items exist [OK]

Common Mistakes:

• Assuming true means no more data
• Confusing hasNextPage with hasPreviousPage
• Ignoring pageInfo in Relay connections

4. You wrote this Relay connection query:

{ comments(last: 3) { edges { node { text } } } }

But the server returns an error:

"Field 'last' is not supported on this connection"

What is the likely cause?

medium

A. The connection does not support backward pagination with 'last'

B. The 'last' argument must be replaced with 'first'

C. The query is missing the 'before' cursor argument

D. The 'edges' field is misspelled

Solution

1. Step 1: Understand Relay pagination directions

   Relay supports forward pagination with first and backward with last.

2. Step 2: Identify server limitation

   Some connections only support forward pagination; thus, last is unsupported.

3. Final Answer:

   The connection does not support backward pagination with 'last' -> Option A

4. Quick Check:

   Unsupported 'last' means no backward pagination [OK]

Hint: Check if connection supports 'last' for backward pagination [OK]

Common Mistakes:

• Replacing 'last' with 'first' without cursor
• Assuming 'edges' spelling causes error
• Ignoring need for 'before' cursor with 'last'

5. You want to fetch a paginated list of products using Relay spec. You need to get the first 3 products, then fetch the next 3 after the last cursor. Which sequence of queries correctly follows Relay pagination?

hard

A. { products(last: 3) { edges { cursor node { name } } pageInfo { startCursor } } }{ products(first: 3, after: "startCursor") { edges { node { name } } } }

B. { products(first: 3) { edges { cursor node { name } } pageInfo { endCursor } } }{ products(last: 3, before: "endCursor") { edges { node { name } } } }

C. { products(first: 3) { edges { cursor node { name } } pageInfo { endCursor } } }{ products(first: 3, after: "endCursor") { edges { node { name } } } }

D. { products(first: 3) { edges { cursor node { name } } pageInfo { endCursor } } }{ products(first: 3, after: "cursor") { edges { node { name } } } }

Solution

1. Step 1: Fetch first 3 products with 'first' and get endCursor

   The first query correctly fetches 3 products and retrieves endCursor for next page.

2. Step 2: Use 'after' with endCursor to fetch next 3 products

   The second query uses after: "endCursor" to continue pagination forward.

3. Final Answer:

   Correct sequence uses 'first' and 'after' with endCursor -> Option C

4. Quick Check:

   Use endCursor with after for next page [OK]

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

Common Mistakes:

• Using last with before for forward pagination
• Passing literal 'cursor' instead of actual endCursor value
• Mixing startCursor with after argument