N+1 problem and solutions in GraphQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the GraphQL query to fetch all users with their posts.

GraphQL

query { users { id name posts { [1] } } }

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Aaddress

Bemail

Cage

Dtitle

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing user fields like email inside posts.

Leaving the posts field empty.

The posts field should include title to fetch post titles.

2fill in blank

medium

Complete the resolver to batch load posts for users to avoid N+1 problem.

GraphQL

const resolvers = { User: { posts: (user, args, context) => context.[1].load(user.id) } };

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ApostLoader

BuserLoader

CcommentLoader

DprofileLoader

Attempts:

3 left

💡 Hint

Common Mistakes

Using loaders unrelated to posts.

Not using any loader causing N+1 queries.

The postLoader batches and caches post fetching by user IDs.

3fill in blank

hard

Fix the error in the DataLoader batch function to correctly group posts by userId.

GraphQL

const batchPosts = async (userIds) => { const posts = await db.posts.find({ userId: { [1]: userIds } }); return userIds.map(id => posts.filter(post => post.userId === id)); };

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Aeq

Bcontains

Cin

Dlike

Attempts:

3 left

💡 Hint

Common Mistakes

Using equality operator which only matches one value.

Using string matching operators incorrectly.

The in operator is used to find posts where userId is in the list of userIds.

4fill in blank

hard

Fill both blanks to complete the GraphQL query and resolver to use DataLoader for comments.

GraphQL

query { posts { id comments { [1] } } } const resolvers = { Post: { comments: (post, args, context) => context.[2].load(post.id) } };

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Atext

BcommentLoader

Cauthor

DuserLoader

Attempts:

3 left

💡 Hint

Common Mistakes

Fetching wrong fields inside comments.

Using wrong loader names causing errors.

The query fetches text of comments, and the resolver uses commentLoader to batch load comments by post ID.

5fill in blank

hard

Fill all three blanks to implement a DataLoader batch function that fetches users by IDs and returns them in order.

GraphQL

const batchUsers = async ([1]) => { const users = await db.users.find({ id: { [2]: [1] } }); return [1].map(id => users.find(user => user.id === id)); };

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

AuserIds

Bin

Deq

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong parameter names.

Using equality operator instead of in.

Not returning users in the order of IDs.

The batch function takes userIds, queries users with in operator, and maps results in the same order as userIds.