Resolver function signature in GraphQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a resolver function in GraphQL?

A resolver function is a function that tells GraphQL how to fetch or compute the data for a specific field in a query.

beginner

What are the four standard parameters of a GraphQL resolver function?

The four standard parameters are:
1. parent (or root) - the result from the parent resolver.
2. args - an object containing the arguments passed to the field.
3. context - shared data available to all resolvers, like authentication info.
4. info - information about the execution state of the query.

beginner

Show a simple resolver function signature in JavaScript for a field named 'user'.

function user(parent, args, context, info) {<br>  // code to fetch user data<br>}

intermediate

Why is the 'context' parameter important in a resolver function?

The 'context' parameter holds shared information like user authentication, database connections, or loaders. It helps resolvers access common resources without passing them explicitly each time.

advanced

What does the 'info' parameter provide in a resolver function?

The 'info' parameter provides details about the execution state of the query, including the field name, path, and the GraphQL schema. It is useful for advanced features like query analysis or optimization.

Which parameter in a resolver function contains the arguments passed in the GraphQL query?

A parent

B context

C info

D args

The 'args' parameter contains the arguments passed to the field in the GraphQL query.

What is the first parameter of a resolver function usually called?

A parent

B context

C args

D info

The first parameter is called 'parent' or 'root' and contains the result from the parent resolver.

Which resolver parameter is commonly used to share authentication data?

A context

B args

C parent

D info

The 'context' parameter is used to share data like authentication info across resolvers.

What does the 'info' parameter NOT provide?

A Field name being resolved

B Arguments passed to the field

C Query execution state

D GraphQL schema details

Arguments are provided in the 'args' parameter, not in 'info'.

Which of these is a valid resolver function signature?

A function resolver(args, parent, context, info)

B function resolver(info, context, args, parent)

C function resolver(parent, args, context, info)

D function resolver(context, args, parent, info)

The correct order is (parent, args, context, info).

Describe the four parameters of a GraphQL resolver function and their roles.

Think about what data each parameter carries and why it is useful.

Explain why the 'context' parameter is useful when writing resolver functions.

Consider what information multiple resolvers might need access to.

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