Resolver function signature in GraphQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a resolver function that receives the parent object.

GraphQL

const resolver = ([1], args, context, info) => { return args.id; }

Drag options to blanks, or click blank then click option'

Aparams

Bparent

Croot

Dsource

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'args' as the first argument instead of 'parent'.

Confusing 'context' with the first argument.

The first argument in a resolver function is commonly called parent. It represents the result returned from the resolver on the parent field.

2fill in blank

medium

Complete the code to access the arguments passed to the resolver.

GraphQL

const resolver = (parent, [1], context, info) => { return args.name; }

Drag options to blanks, or click blank then click option'

Aargs

Bvariables

Cparams

Dinputs

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'params' or 'variables' instead of 'args'.

Trying to access arguments from the 'context' argument.

The second argument in a resolver function is args. It contains the arguments passed to the field in the query.

3fill in blank

hard

Fix the error in the resolver signature by correctly naming the context argument.

GraphQL

const resolver = (parent, args, [1], info) => { return context.user.id; }

Drag options to blanks, or click blank then click option'

Arequest

Bctx

Ccontext

Dsession

Attempts:

3 left

💡 Hint

Common Mistakes

Naming the context argument incorrectly as 'request' or 'session'.

Confusing context with info argument.

The third argument is context. It provides shared data like authentication info to all resolvers.

4fill in blank

hard

Fill both blanks to complete the resolver function signature with correct argument names.

GraphQL

const resolver = ([1], [2], context, info) => { return args.id; }

Drag options to blanks, or click blank then click option'

Aparent

Bargs

Cparams

Dsource

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the order of parent and args.

Using 'params' instead of 'args'.

The first two arguments are parent and args. They represent the parent object and the arguments passed to the field.

5fill in blank

hard

Fill all three blanks to complete the full resolver function signature with correct argument names.

GraphQL

const resolver = ([1], [2], [3], info) => { return context.user; }

Drag options to blanks, or click blank then click option'

Aparent

Bargs

Ccontext

Drequest

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'request' instead of 'context'.

Changing the order of arguments.

The resolver function signature is (parent, args, context, info). These arguments provide data from the parent, the query arguments, shared context, and query info.

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