Context argument in GraphQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to access the context argument in a resolver function.

GraphQL

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

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

Ainfo

Bcontext

Cargs

Dparent

Attempts:

3 left

💡 Hint

Common Mistakes

Using args or parent instead of context to get user info.

Confusing the order of resolver arguments.

The context argument provides shared data like authentication info to resolvers.

2fill in blank

medium

Complete the code to extract the user role from the context argument.

GraphQL

function checkRole(_, __, [1]) { return [1].user.role; }

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

Ainfo

Bargs

Ccontext

Dparent

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to get user role from args or parent.

Using the wrong argument position.

The context holds the current user's data, including roles.

3fill in blank

hard

Fix the error in accessing the context argument in this resolver.

GraphQL

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

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

Ainfo

Bargs

Ccontext

Dparent

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to use context (undefined) or args/parent instead of info.

Not passing context properly to resolvers.

Although named info, the third argument holds the context with user data (true info metadata is fourth). Use info here.

4fill in blank

hard

Fill both blanks to correctly use context and args in a resolver.

GraphQL

const resolver = (parent, [1], [2]) => { return [2].user.id === [1].id; }

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

Aargs

Bcontext

Cinfo

Dparent

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping args and context positions.

Using info instead of context.

args holds input arguments, context holds user info.

5fill in blank

hard

Fill all three blanks to destructure context and use args in a resolver.

GraphQL

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

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

Aargs

Bcontext

Cinfo

Dparent

Attempts:

3 left

💡 Hint

Common Mistakes

Using info or parent instead of context.

Mixing up args and context.

We destructure user from context and compare with args.

Practice

1. What is the main purpose of the context argument in GraphQL resolvers?

easy

A. To format the response data before sending it to the client

B. To define the GraphQL schema types

C. To specify the query operation type (query, mutation, subscription)

D. To share common data like authentication or database access across all resolvers during a request

Solution

1. Step 1: Understand the role of context in GraphQL

   The context argument is designed to hold data shared by all resolvers during a single request, such as authentication info or database connections.

2. Step 2: Compare with other options

   Defining schema types, specifying operation types, or formatting responses are handled elsewhere, not by context.

3. Final Answer:

   To share common data like authentication or database access across all resolvers during a request -> Option D

4. Quick Check:

   Context = Shared data for resolvers [OK]

Hint: Context holds shared info for all resolvers in a request [OK]

Common Mistakes:

• Confusing context with schema definition
• Thinking context formats responses
• Assuming context defines operation types

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

easy

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

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

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

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

Solution

1. Step 1: Recall resolver function signature

   GraphQL resolvers receive arguments in the order: parent, args, context.

2. Step 2: Match the correct order

   Only resolver(parent, args, context) { ... } matches this order correctly.

3. Final Answer:

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

4. Quick Check:

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

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

Common Mistakes:

• Swapping context and args positions
• Omitting the parent argument
• Using only two arguments instead of three

3. Given this resolver code snippet:

const resolver = (parent, args, context) => {
  return context.db.getUserById(args.id);
};

What will resolver(null, {id: 5}, context) return if context.db.getUserById(5) returns { id: 5, name: 'Alice' }?

medium

A. null

B. { id: 5, name: 'Alice' }

C. undefined

D. Error: getUserById is not a function

Solution

1. Step 1: Understand the resolver call

   The resolver calls context.db.getUserById with args.id which is 5.

2. Step 2: Check the return value from context

   Given context.db.getUserById(5) returns { id: 5, name: 'Alice' }, the resolver returns this object.

3. Final Answer:

   { id: 5, name: 'Alice' } -> Option B

4. Quick Check:

   Resolver returns context.db.getUserById(args.id) result [OK]

Hint: Resolver returns what context function returns for given args [OK]

Common Mistakes:

• Assuming resolver returns null or undefined
• Confusing parent argument with context
• Expecting an error without checking context structure

4. Consider this resolver code:

const resolver = (parent, args, context) => {
  return context.getUser(args.id);
};

If running this code causes TypeError: context.getUser is not a function, what is the most likely cause?

medium

A. The context object does not have a getUser method

B. The args.id is undefined

C. The parent argument is missing

D. The resolver function is missing the args parameter

Solution

1. Step 1: Analyze the error message

   The error says getUser is not a function on context, meaning context.getUser is undefined or not callable.

2. Step 2: Check other options

   Undefined args.id or missing parent won't cause this specific error. Missing args parameter would cause a different error.

3. Final Answer:

   The context object does not have a getUser method -> Option A

4. Quick Check:

   TypeError means missing method on context [OK]

Hint: TypeError means method missing on context object [OK]

Common Mistakes:

• Blaming args.id for method not found error
• Assuming parent argument causes this error
• Ignoring that context must have the method

5. You want to add user authentication info to all resolvers using the context argument. Which approach correctly sets up the context for this purpose?

hard

A. Pass user info as an argument in every query instead of context

B. Define user info inside each resolver separately without using context

C. Create context once per request including user info, then pass it to all resolvers

D. Use global variables to store user info accessible by resolvers

Solution

1. Step 1: Understand context usage for shared data

   Context is designed to be created once per request and shared with all resolvers, perfect for authentication info.

2. Step 2: Evaluate other options

   Defining user info inside each resolver duplicates code; passing user info as query args is insecure and inconvenient; global variables are unsafe for concurrent requests.

3. Final Answer:

   Create context once per request including user info, then pass it to all resolvers -> Option C

4. Quick Check:

   Context = single shared object per request [OK]

Hint: Set context once per request with user info for all resolvers [OK]

Common Mistakes:

• Duplicating user info in every resolver
• Passing sensitive info as query arguments
• Using global variables causing data leaks