Info argument in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Understanding the Info Argument Structure

Given a GraphQL resolver function that receives the info argument, what does info.fieldName return?

GraphQL

function resolver(parent, args, context, info) {
  return info.fieldName;
}

A The root query type name

B The entire GraphQL query string sent by the client

C The context object passed to all resolvers

D The name of the field currently being resolved

💡 Hint

Think about what part of the query the resolver is working on.

The info.fieldName property contains the name of the field that the resolver is currently resolving. It helps identify which field in the query is being processed.

❓ query_result

intermediate

Using Info to Access Requested Subfields

In a resolver, how can you use the info argument to find out which subfields the client requested for a nested object?

GraphQL

function resolver(parent, args, context, info) {
  // What property of info helps here?
  return Object.keys(info.fieldNodes[0].selectionSet.selections);
}

A info.schema.getType() returns the requested subfields

B info.fieldNodes[0].selectionSet.selections contains the requested subfields

C info.variableValues holds the subfield names

D info.rootValue contains the subfield list

💡 Hint

Look inside the AST nodes in the info argument.

The info.fieldNodes array contains the AST nodes for the current field. The first node's selectionSet.selections holds the subfields requested by the client.

📝 Syntax

advanced

Correct Usage of Info Argument in Resolver Signature

Which of the following resolver function signatures correctly includes the info argument as the fourth parameter?

A function resolver(parent, args, context, info) { return info.fieldName; }

B function resolver(info, parent, args, context) { return info.fieldName; }

C function resolver(parent, info, args, context) { return info.fieldName; }

D function resolver(parent, args, info) { return info.fieldName; }

💡 Hint

Remember the standard order of resolver parameters.

The standard resolver function parameters order is parent, args, context, then info. Only option A follows this order correctly.

🧠 Conceptual

advanced

Purpose of the Info Argument in GraphQL Resolvers

What is the main purpose of the info argument passed to GraphQL resolvers?

A To store user authentication tokens for security checks

B To hold the database connection object for queries

C To provide detailed information about the execution state, including the query AST and schema details

D To cache previous query results for faster responses

💡 Hint

Think about what extra data the resolver might need about the query itself.

The info argument contains the GraphQL query's abstract syntax tree (AST), schema information, and execution state, which helps resolvers understand the query structure and requested fields.

🔧 Debug

expert

Diagnosing a TypeError Using the Info Argument

A resolver function tries to access info.fieldNodes.selectionSet.selections but throws a TypeError: Cannot read property 'selectionSet' of undefined. What is the most likely cause?

GraphQL

function resolver(parent, args, context, info) {
  return info.fieldNodes.selectionSet.selections;
}

A info.fieldNodes is an array, so accessing selectionSet directly causes the error

B info.fieldNodes is null because the query is empty

C info.selectionSet is undefined because it does not exist on info

D The resolver forgot to pass the info argument

💡 Hint

Check the type of info.fieldNodes and how to access its elements.

info.fieldNodes is an array of AST nodes. Trying to access selectionSet directly on the array causes the error. The correct access is info.fieldNodes[0].selectionSet.

Practice

1. What is the purpose of the info argument in a GraphQL resolver?

easy

A. It stores the database connection details.

B. It contains the user's authentication token.

C. It tells the resolver which fields the client requested.

D. It defines the schema of the GraphQL server.

Solution

1. Step 1: Understand the role of resolver arguments

   Resolvers receive arguments like parent, args, context, and info. Each has a specific role.

2. Step 2: Identify what info provides

   The info argument contains details about the query, including which fields the client requested.

3. Final Answer:

   It tells the resolver which fields the client requested. -> Option C

4. Quick Check:

   Info argument = requested fields [OK]

Hint: Info shows requested fields to optimize data fetching [OK]

Common Mistakes:

• Confusing info with context or args
• Thinking info holds authentication data
• Assuming info defines schema

2. Which of the following is the correct way to include the info argument in a GraphQL resolver function?

easy

A. resolver(parent, args, context, info) { ... }

B. resolver(args, parent, info, context) { ... }

C. resolver(context, info, args, parent) { ... }

D. resolver(info, parent, args, context) { ... }

Solution

1. Step 1: Recall the standard resolver signature

   The standard order is (parent, args, context, info) in GraphQL resolvers.

2. Step 2: Match the correct order

   resolver(parent, args, context, info) { ... } matches this order exactly, making it the correct syntax.

3. Final Answer:

   resolver(parent, args, context, info) { ... } -> Option A

4. Quick Check:

   Resolver args order = parent, args, context, info [OK]

Hint: Remember resolver args order: parent, args, context, info [OK]

Common Mistakes:

• Mixing up the order of arguments
• Placing info before context
• Omitting info argument

3. Given this resolver snippet, what will info.fieldNodes[0].selectionSet.selections.map(f => f.name.value) return if the client queries { user { id name } }?

medium

A. ["id", "name"]

B. ["user"]

C. ["id"]

D. An empty array []

Solution

1. Step 1: Understand the query structure

   The client requests the fields id and name inside user.

2. Step 2: Analyze the info.fieldNodes access

   info.fieldNodes[0].selectionSet.selections lists the fields requested inside user, which are id and name.

3. Final Answer:

   ["id", "name"] -> Option A

4. Quick Check:

   info.fieldNodes selections = requested fields [OK]

Hint: info.fieldNodes lists requested fields inside current resolver [OK]

Common Mistakes:

• Returning parent field name instead of subfields
• Confusing selectionSet with fieldNodes
• Expecting only one field instead of all requested

4. You wrote this resolver: function resolver(parent, args, context) { return info.fieldNodes; }. Why does this cause an error?

medium

A. You cannot access fieldNodes inside resolvers.

B. The resolver is missing the info argument in its parameters.

C. The info argument must be the first parameter.

D. Resolvers cannot return objects like fieldNodes.

Solution

1. Step 1: Check resolver parameters

   The resolver only has three parameters: parent, args, context. It lacks the fourth parameter info.

2. Step 2: Understand usage of info

   Since info is not declared, trying to use it causes a reference error.

3. Final Answer:

   The resolver is missing the info argument in its parameters. -> Option B

4. Quick Check:

   Missing info param = error [OK]

Hint: Always include info as fourth parameter to use it [OK]

Common Mistakes:

• Forgetting to add info parameter
• Assuming info is global or in context
• Misordering resolver parameters

5. You want your resolver to return only the fields requested by the client to save resources. Which approach using the info argument is best?

hard

A. Fetch all fields but filter results after sending to client.

B. Ignore info and always fetch all fields from the database.

C. Use args to guess which fields the client wants.

D. Use info.fieldNodes to find requested fields and fetch only those from the database.

Solution

1. Step 1: Understand the goal

   The goal is to fetch only requested fields to save resources.

2. Step 2: Use info to get requested fields

   info.fieldNodes provides the exact fields the client asked for, so you can fetch only those.

3. Step 3: Compare options

   Use info.fieldNodes to find requested fields and fetch only those from the database. uses info correctly. Options B, C, and D either waste resources or guess incorrectly.

4. Final Answer:

   Use info.fieldNodes to find requested fields and fetch only those from the database. -> Option D

5. Quick Check:

   Use info to fetch requested fields only [OK]

Hint: Fetch only requested fields using info to save resources [OK]

Common Mistakes:

• Fetching all data regardless of request
• Using args instead of info for fields
• Filtering after fetching all data