Context setup in GraphQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a GraphQL context parameter in the resolver function.

GraphQL

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

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

Acontext

Binfo

Croot

Dparams

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'info' or 'root' instead of 'context' for shared data.

Confusing the order of resolver parameters.

The third parameter in a GraphQL resolver is usually called context. It holds shared data like authentication info.

2fill in blank

medium

Complete the code to access the user ID from the context inside a resolver.

GraphQL

const userId = [1].user.id;

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

Aargs

Binfo

Cparent

Dcontext

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to get user ID from args or parent instead of context.

Using 'info' which holds query info, not user data.

The context object contains shared info like the authenticated user. Access user ID via context.user.id.

3fill in blank

hard

Fix the error in the resolver to correctly destructure context and get the database client.

GraphQL

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

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

Acontext

Bctx

Cinfo

Dparams

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different parameter name than the variable inside the function.

Not destructuring the context object properly.

The parameter name must match the variable used inside the function. Here, context is used, so it must be the parameter name.

4fill in blank

hard

Fill both blanks to correctly pass context to the Apollo Server constructor.

GraphQL

const server = new ApolloServer({ typeDefs, resolvers, [1]: () => ([2]) });

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

Acontext

B{ user: currentUser }

Cschema

Dargs

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'schema' or 'args' instead of 'context' option.

Not returning an object from the context function.

The context option is a function returning an object with shared data like the current user.

5fill in blank

hard

Fill all three blanks to create a resolver that uses context to check user role and fetch data.

GraphQL

const resolver = (parent, args, [1]) => { if (![2].user || [3].user.role !== 'admin') { throw new Error('Unauthorized'); } return [2].db.getData(args.id); }

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

Acontext

Cctx

Dinfo

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing different names for context parameter.

Not checking if user exists before accessing role.

The resolver uses the context parameter (also called ctx sometimes) to check user info and access the database. Here, the same context object is used multiple times.

Practice

1. What is the main purpose of the context in a GraphQL server?

easy

A. To share data like user info or database clients across all resolvers

B. To define the GraphQL schema types

C. To write the query resolvers

D. To format the GraphQL query response

Solution

1. Step 1: Understand what context provides

   Context is an object that runs once per request and is accessible in every resolver, allowing shared data like user info or database clients.

2. Step 2: Compare with other options

   Defining schema types, writing resolvers, and formatting responses are separate tasks not handled by context.

3. Final Answer:

   To share data like user info or database clients across all resolvers -> Option A

4. Quick Check:

   Context shares data across resolvers [OK]

Hint: Context shares common data across resolvers per request [OK]

Common Mistakes:

• Confusing context with schema definition
• Thinking context formats responses
• Assuming context writes resolver logic

2. Which of the following is the correct way to define a context function in Apollo Server?

easy

A. context = { user: getUser() }

B. context: () => ({ user: getUser() })

C. context: { user: getUser() }

D. context() { return user: getUser() }

Solution

1. Step 1: Recall Apollo Server context syntax

   Context is defined as a function returning an object, e.g., context: () => ({ user: getUser() }).

2. Step 2: Identify syntax errors in other options

   context = { user: getUser() } uses assignment instead of a function, C uses an object directly without a function, and D has invalid syntax missing parentheses and braces.

3. Final Answer:

   context: () => ({ user: getUser() }) -> Option B

4. Quick Check:

   Context is a function returning an object [OK]

Hint: Context must be a function returning an object [OK]

Common Mistakes:

• Defining context as a plain object
• Missing parentheses in function syntax
• Using assignment instead of property

3. Given this context setup in Apollo Server:

context: () => ({ user: { id: 5, name: 'Alice' } })

What will be the value of context.user.name inside a resolver?

medium

A. undefined

B. 5

C. null

D. 'Alice'

Solution

1. Step 1: Analyze the context object

   The context function returns an object with a user property containing { id: 5, name: 'Alice' }.

2. Step 2: Access user.name in resolver

   Accessing context.user.name will give the string 'Alice' as defined.

3. Final Answer:

   'Alice' -> Option D

4. Quick Check:

   context.user.name = 'Alice' [OK]

Hint: Context returns user object; access properties directly [OK]

Common Mistakes:

• Confusing user id with name
• Assuming context is undefined
• Expecting null instead of string

4. You wrote this context function:

context: () => { user: getUser() }

Why does context.user return undefined in resolvers?

medium

A. Because user is not a valid property

B. Because getUser() is undefined

C. Because the function does not return the object explicitly

D. Because context must be an object, not a function

Solution

1. Step 1: Check function return behavior

   The function uses curly braces but lacks a return statement, so it returns undefined by default.

2. Step 2: Understand impact on context

   Since nothing is returned, context.user is undefined in resolvers.

3. Final Answer:

   Because the function does not return the object explicitly -> Option C

4. Quick Check:

   Missing return in function = undefined context [OK]

Hint: Use return or parentheses to return object in arrow function [OK]

Common Mistakes:

• Omitting return in arrow function with braces
• Assuming getUser() is undefined without checking
• Thinking context must be an object, not function

5. You want to add a database client and user info to context for each request. Which is the best way to do this in Apollo Server?

hard

A. context: async () => { const db = await connectDB(); const user = await getUser(); return { db, user }; }

B. context: { db: connectDB(), user: getUser() }

C. context: () => { db: connectDB(); user: getUser(); }

D. context: () => ({ db: connectDB(), user: getUser() })

Solution

1. Step 1: Understand async context needs

   Connecting to a database and fetching user info are asynchronous operations, so context must be async and await these calls.

2. Step 2: Evaluate options for async correctness

   context: async () => { const db = await connectDB(); const user = await getUser(); return { db, user }; } correctly uses async function and awaits results before returning an object. context: { db: connectDB(), user: getUser() } is a plain object, not a function. context: () => { db: connectDB(); user: getUser(); } lacks return and awaits. context: () => ({ db: connectDB(), user: getUser() }) returns an object but does not await async calls.

3. Final Answer:

   context: async () => { const db = await connectDB(); const user = await getUser(); return { db, user }; } -> Option A

4. Quick Check:

   Async context with awaited data [OK]

Hint: Use async function and await for async data in context [OK]

Common Mistakes:

• Not awaiting async calls in context
• Using plain object instead of function
• Missing return statement in function