Context setup in GraphQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of context in GraphQL?

Context in GraphQL is used to share data, like authentication info or database connections, across all resolvers during a query execution.

beginner

How do you typically provide context in a GraphQL server?

You provide context by defining a function or object when setting up the GraphQL server that runs for each request, passing shared data to resolvers.

intermediate

Why is context important for authentication in GraphQL?

Context allows you to pass user authentication details to resolvers so they can check permissions before returning data.

intermediate

Can context be different for each GraphQL request? Why?

Yes, context is created fresh for each request to keep data isolated and secure between users.

beginner

Give an example of what might be included in GraphQL context.

Examples include the current user info, database connection, caching tools, or API keys needed by resolvers.

What is the main role of context in a GraphQL server?

A To define the GraphQL schema

B To format the GraphQL query

C To store query results permanently

D To share data between resolvers during a request

Context shares data like authentication or database connections between resolvers during a single request.

When is the context object created in a GraphQL server?

A For each incoming request

B When the schema is built

C Only when a mutation is called

D Once when the server starts

Context is created fresh for each request to keep data isolated and secure.

Which of these is NOT typically included in GraphQL context?

A User authentication info

B Database connection

C GraphQL query text

D API keys

The query text is handled separately; context holds shared data like user info or connections.

Why should context be different for each request?

A To improve query speed

B To isolate user data and maintain security

C To reduce server memory usage

D To cache query results

Different context per request keeps user data isolated and secure.

How do resolvers access the context in GraphQL?

A Through the third argument

B Through the second argument

C Through the first argument

D Through a global variable

Resolvers receive context as the third argument in their function signature.

Explain what GraphQL context is and why it is useful.

Think about what data resolvers need to share during a query.

Describe how you would set up context in a GraphQL server and what you might include in it.

Consider what information resolvers need to access for each request.

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