Query complexity analysis in GraphQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a GraphQL query that fetches a user's name.

GraphQL

query GetUserName { user(id: 1) { [1] } }

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

Aname

Bage

Cemail

Daddress

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a field that does not exist in the user type.

Selecting a field that fetches unrelated data.

The field name correctly fetches the user's name in the query.

2fill in blank

medium

Complete the code to add a nested field to fetch the user's posts titles.

GraphQL

query GetUserPosts { user(id: 1) { name posts { [1] } } }

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Adate

Bcontent

Ctitle

Dcomments

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting content instead of title when only titles are needed.

Choosing unrelated fields like comments.

The title field fetches the titles of the user's posts.

3fill in blank

hard

Fix the error in the query by selecting the correct field to limit the number of posts fetched.

GraphQL

query GetLimitedPosts { user(id: 1) { posts([1]: 5) { title } } }

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Amax

Bcount

Csize

Dlimit

Attempts:

3 left

💡 Hint

Common Mistakes

Using count or max which are not valid argument names here.

Using size which is not recognized by the schema.

The limit argument is commonly used to restrict the number of items returned.

4fill in blank

hard

Fill both blanks to create a query that fetches users with their posts filtered by a minimum number of likes.

GraphQL

query GetPopularPosts { users { name posts(filter: { likes: { [1]: [2] } }) { title } } }

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Agt

B10

Clt

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using lt when filtering for popular posts.

Choosing a too low number that doesn't filter effectively.

The filter uses likes: { gt: 10 } to get posts with more than 10 likes.

5fill in blank

hard

Fill all three blanks to write a query that fetches posts with title, author name, and comments count greater than 5.

GraphQL

query GetDetailedPosts { posts(filter: { comments: { [1]: [2] } }) { [3] author { name } } }

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

Agt

B5

Ctitle

Dcontent

Attempts:

3 left

💡 Hint

Common Mistakes

Using content instead of title when only the title is requested.

Using incorrect operators like lt in the filter.

The query filters posts with comments: { gt: 5 } and fetches the title and author's name.

Practice

1. What is the main purpose of query complexity analysis in GraphQL?

easy

A. To measure how resource-heavy a query is before execution

B. To change the data returned by a query

C. To write queries faster

D. To store query results in cache

Solution

1. Step 1: Understand query complexity analysis

   It estimates how much work a query will cause the server to do before running it.

2. Step 2: Identify the main goal

   This helps prevent very heavy queries that slow down or crash the server.

3. Final Answer:

   To measure how resource-heavy a query is before execution -> Option A

4. Quick Check:

   Query complexity = resource estimation [OK]

Hint: Think: Why check query cost before running? To protect server [OK]

Common Mistakes:

• Confusing complexity analysis with caching
• Thinking it changes query results
• Assuming it speeds up query writing

2. Which of the following is a correct way to define a complexity rule in a GraphQL server?

easy

A. Adding a complexity function to field definitions

B. Writing complexity inside the GraphQL query itself

C. Using @complexity directive in the query

D. Setting complexity in the client application

Solution

1. Step 1: Recall where complexity rules are set

   Complexity rules are added in the server schema code, usually as functions on fields.

2. Step 2: Eliminate wrong options

   Complexity is not set inside queries, directives, or client apps.

3. Final Answer:

   Adding a complexity function to field definitions -> Option A

4. Quick Check:

   Complexity rules = server schema code [OK]

Hint: Complexity rules live on server fields, not in queries [OK]

Common Mistakes:

• Trying to add complexity in the query text
• Using non-existent directives for complexity
• Setting complexity on client side

3. Given this GraphQL query and complexity rules:

{ user { posts { comments } } }

If user has complexity 1, posts complexity 5, and comments complexity 2, what is the total complexity?

medium

A. 8

B. 15

C. 7

D. 10

Solution

1. Step 1: Identify field complexities

   user = 1, posts = 5, comments = 2.

2. Step 2: Calculate for nested fields

   Nested field complexities are multiplied: 1 x 5 x 2 = 10.

3. Final Answer:

   10 -> Option D

4. Quick Check:

   Nested fields multiply complexity = 1*5*2=10 [OK]

Hint: Multiply all nested field complexities: 1 x 5 x 2 = 10 [OK]

Common Mistakes:

• Adding all numbers without multiplication
• Ignoring nested field multiplication
• Choosing sum instead of product for nested fields

4. You wrote a complexity function for a field but your server crashes on some queries. What is a likely cause?

medium

A. The query is missing required fields

B. You forgot to add the field to the schema

C. The complexity function returns a non-numeric value

D. The client sent an invalid query syntax

Solution

1. Step 1: Understand complexity function requirements

   Complexity functions must return numbers representing cost.

2. Step 2: Identify crash cause

   If the function returns a string or undefined, the server cannot calculate total complexity and crashes.

3. Final Answer:

   The complexity function returns a non-numeric value -> Option C

4. Quick Check:

   Complexity function must return number [OK]

Hint: Ensure complexity functions return numbers only [OK]

Common Mistakes:

• Returning strings or null from complexity functions
• Ignoring schema registration of fields
• Blaming client query syntax for server crashes

5. You want to limit your GraphQL server to reject queries with complexity over 100. Which approach correctly implements this?

hard

A. Modify client queries to never exceed 100 complexity

B. Add a complexity rule that calculates total cost and rejects queries above 100

C. Use a directive in queries to mark complexity limits

D. Increase server timeout to handle heavy queries

Solution

1. Step 1: Understand server-side complexity limiting

   The server must calculate query complexity and reject queries exceeding the limit.

2. Step 2: Evaluate options

   Only adding a complexity rule on the server can enforce this limit automatically.

3. Final Answer:

   Add a complexity rule that calculates total cost and rejects queries above 100 -> Option B

4. Quick Check:

   Server enforces limits via complexity rules [OK]

Hint: Limit complexity on server, not client or query text [OK]

Common Mistakes:

• Trying to limit complexity from client side
• Using query directives which don't enforce limits
• Increasing timeout instead of limiting complexity