Resolver function signature in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Identify the correct resolver function signature

Which of the following is the correct signature for a GraphQL resolver function?

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

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

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

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

💡 Hint

Remember the order: parent, arguments, context, and info.

The standard resolver function signature in GraphQL is function resolver(parent, args, context, info). This order is important because GraphQL passes these parameters in this sequence.

❓ query_result

intermediate

Output of resolver accessing arguments

Given this resolver function, what will be the output if called with args = { id: 5 }? function resolver(parent, args, context, info) { return args.id * 2; }

GraphQL

function resolver(parent, args, context, info) {
  return args.id * 2;
}

A undefined

B 5

C NaN

D 10

💡 Hint

Look at how the argument 'id' is used inside the function.

The resolver multiplies the id argument by 2. Since id is 5, the output is 10.

📝 Syntax

advanced

Identify the syntax error in resolver function

Which option contains a syntax error in the resolver function signature?

A const resolver = (parent, args, context, info) => { return args.value; }

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

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

D const resolver = function(parent, args, context, info) { return args.value; }

💡 Hint

Check the commas between parameters.

Option B is missing a comma between parent and args, causing a syntax error.

❓ optimization

advanced

Best practice for using context in resolver

Which option shows the best practice for accessing user information from context inside a resolver?

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

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

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

D function resolver(parent, args, context, info) { return info.user.id; }

💡 Hint

User info is usually stored in context, not args or parent.

Context is the place to store per-request data like authenticated user info. Accessing context.user.id is the best practice.

🔧 Debug

expert

Why does this resolver throw an error?

Consider this resolver: function resolver(parent, args, context, info) { return args.input.value; } If the query is called without the 'input' argument, what error will occur?

A TypeError: Cannot read property 'value' of undefined

B ReferenceError: input is not defined

C SyntaxError: Unexpected token

D No error, returns undefined

💡 Hint

What happens if you try to access a property of undefined?

If args.input is undefined, trying to access value on it causes a TypeError.

Practice

1. Which of the following best describes the purpose of a resolver function in GraphQL?

easy

A. It handles user authentication outside of GraphQL.

B. It connects a GraphQL query to the actual data source and returns data.

C. It formats the GraphQL query string before sending it to the server.

D. It defines the schema types and fields in GraphQL.

Solution

1. Step 1: Understand resolver role

   Resolvers are functions that fetch or compute data for a GraphQL query.

2. Step 2: Match purpose to options

   Only It connects a GraphQL query to the actual data source and returns data. correctly states that resolvers connect queries to data sources and return data.

3. Final Answer:

   It connects a GraphQL query to the actual data source and returns data. -> Option B

4. Quick Check:

   Resolver function purpose = Connect query to data [OK]

Hint: Resolvers fetch data for queries, not define schema [OK]

Common Mistakes:

• Confusing resolvers with schema definitions
• Thinking resolvers format queries
• Assuming resolvers handle authentication only

2. Which of the following is the correct signature of a GraphQL resolver function?

easy

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

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

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

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

Solution

1. Step 1: Recall resolver argument order

   The standard order is parent, args, context, info.

2. Step 2: Compare options to standard order

   Only function resolver(parent, args, context, info) { ... } matches the correct order exactly.

3. Final Answer:

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

4. Quick Check:

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

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

Common Mistakes:

• Mixing up the order of arguments
• Omitting required arguments
• Using incorrect argument names

3. Given the resolver function below, what will be the returned value if args = { id: 5 } and parent = null?

function resolver(parent, args, context, info) {
  return args.id * 2;
}

medium

A. 10

B. 5

C. undefined

D. Error

Solution

1. Step 1: Identify input values

   args.id is 5, parent is null but unused.

2. Step 2: Calculate return value

   Return is args.id * 2 = 5 * 2 = 10.

3. Final Answer:

   10 -> Option A

4. Quick Check:

   args.id * 2 = 10 [OK]

Hint: Focus on args usage inside resolver [OK]

Common Mistakes:

• Confusing parent with args
• Assuming parent affects output here
• Expecting an error due to null parent

4. Identify the error in the following resolver function signature:

const resolver = (args, parent, context, info) => {
  return parent.value + args.increment;
}

medium

A. The order of arguments is incorrect; parent should be first.

B. The function should not use arrow syntax for resolvers.

C. The resolver must return a Promise, not a direct value.

D. The argument names are invalid and must be capitalized.

Solution

1. Step 1: Check argument order

   Resolvers must have arguments in order: parent, args, context, info.

2. Step 2: Identify mismatch

   This function has args first, then parent, which is incorrect.

3. Final Answer:

   The order of arguments is incorrect; parent should be first. -> Option A

4. Quick Check:

   Argument order must be parent first [OK]

Hint: Always put parent as first argument [OK]

Common Mistakes:

• Swapping parent and args positions
• Thinking arrow functions are invalid
• Assuming return must be Promise always

5. You want to write a resolver that fetches a user by ID and also logs the request info. Which resolver signature and implementation correctly uses all four arguments to achieve this?

hard

A. function resolver(parent, args, context, info) {
return db.getUser(args.id);
console.log(info.operation);
}

B. function resolver(args, parent, context, info) {
console.log(args.id);
return context.db.getUserById(args.id);
}

C. function resolver(parent, args, context) {
console.log(context);
return db.getUser(args.id);
}

D. function resolver(parent, args, context, info) {
console.log(info.fieldName);
return context.db.getUserById(args.id);
}

Solution

1. Step 1: Verify argument order and usage

   function resolver(parent, args, context, info) { console.log(info.fieldName); return context.db.getUserById(args.id); } uses correct argument order and logs info.fieldName before returning data.

2. Step 2: Check context usage for data fetching

   function resolver(parent, args, context, info) { console.log(info.fieldName); return context.db.getUserById(args.id); } correctly calls context.db.getUserById with args.id.

3. Step 3: Review other options for errors

   Options B and C have wrong argument order or missing info; D logs after return, so log never runs.

4. Final Answer:

   function resolver(parent, args, context, info) { console.log(info.fieldName); return context.db.getUserById(args.id); } -> Option D

5. Quick Check:

   Correct signature and usage = function resolver(parent, args, context, info) { console.log(info.fieldName); return context.db.getUserById(args.id); } [OK]

Hint: Log info before return; use correct argument order [OK]

Common Mistakes:

• Logging after return statement
• Incorrect argument order
• Not using context for data access