Field-level cost analysis in GraphQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to request the cost of a specific field in a GraphQL query.

GraphQL

query { user { name [1] } }

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

A@deprecated(reason: "old")

B@cost(complexity: 2)

C@cost(complexity: 5)

D@include(if: true)

Attempts:

3 left

💡 Hint

Common Mistakes

Using @deprecated instead of @cost.

Omitting the complexity value.

Using directives unrelated to cost.

The @cost directive with complexity: 5 specifies the cost for the name field.

2fill in blank

medium

Complete the code to add a cost directive with a multiplier to a nested field.

GraphQL

query { product { price [1] } }

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

A@cost(multiplier: 3)

B@cost(complexity: 1)

C@skip(if: false)

D@deprecated(reason: "unused")

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing multiplier with complexity.

Using unrelated directives.

Missing the multiplier argument.

The @cost(multiplier: 3) directive multiplies the cost of the price field by 3.

3fill in blank

hard

Fix the error in the cost directive syntax for the field.

GraphQL

query { order { totalPrice [1] } }

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

A@cost(complexity: 4)

B@cost[complexity:4]

C@cost(complexity=4)

D@cost complexity: 4

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting parentheses.

Using equal signs instead of colons.

Using square brackets instead of parentheses.

The correct syntax for directives uses parentheses and colon-separated arguments, like @cost(complexity: 4).

4fill in blank

hard

Fill both blanks to correctly apply cost directives with complexity and multiplier.

GraphQL

query { user { posts [1] comments [2] } }

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

A@cost(complexity: 3)

B@cost(multiplier: 2)

C@cost(complexity: 1)

D@deprecated(reason: "old")

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up complexity and multiplier values.

Using deprecated directive instead of cost.

Applying directives incorrectly.

The posts field has a complexity of 3, and the comments field has a multiplier of 2 to scale its cost.

5fill in blank

hard

Fill all three blanks to define a query with cost directives specifying complexity, multiplier, and a nested field cost.

GraphQL

query { shop [1] products [2] reviews [3] }

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

A@cost(complexity: 5)

B@cost(multiplier: 4)

C@cost(complexity: 2)

D@skip(if: false)

Attempts:

3 left

💡 Hint

Common Mistakes

Using skip directive instead of cost.

Confusing complexity and multiplier values.

Incorrect directive syntax.

The shop field has complexity 5, products has a multiplier of 4, and reviews has complexity 2 to define their costs.

Practice

1. What is the main purpose of using the @cost directive in GraphQL field-level cost analysis?

easy

A. To rename a field in the schema

B. To define the data type of a field

C. To specify the default value of a field

D. To assign a numeric cost to each field to track resource usage

Solution

1. Step 1: Understand the purpose of field-level cost analysis

   Field-level cost analysis helps monitor and limit resource use by assigning costs to fields.

2. Step 2: Identify the role of the @cost directive

   The @cost directive assigns a numeric complexity cost to each field to estimate query cost.

3. Final Answer:

   To assign a numeric cost to each field to track resource usage -> Option D

4. Quick Check:

   @cost assigns cost = A [OK]

Hint: Remember: @cost tracks resource use per field [OK]

Common Mistakes:

• Confusing cost with data type definition
• Thinking @cost renames fields
• Assuming it sets default values

2. Which of the following is the correct syntax to add a cost directive with complexity 5 to a GraphQL field named books?

easy

A. books: [Book] @cost(complexity: 5)

B. books: [Book] @cost(5)

C. books: [Book] @cost(complexity=5)

D. books: [Book] @cost { complexity: 5 }

Solution

1. Step 1: Recall the correct directive syntax

   The @cost directive uses parentheses with named arguments, e.g., @cost(complexity: 5).

2. Step 2: Check each option's syntax

   books: [Book] @cost(complexity: 5) uses correct syntax with named argument and colon. The other three options use incorrect syntax forms.

3. Final Answer:

   books: [Book] @cost(complexity: 5) -> Option A

4. Quick Check:

   Correct directive syntax = B [OK]

Hint: Use parentheses and colon for directive args: @cost(complexity: 5) [OK]

Common Mistakes:

• Using equal sign instead of colon
• Omitting parentheses
• Using braces instead of parentheses

3. Given the schema snippet:

type Query {
  users: [User] @cost(complexity: 2, multipliers: ["first"])
}

input UserFilter {
  first: Int
}

And the query:

{ users(first: 3) { id name } }

What is the total cost of this query assuming id and name fields have cost 1 each?

medium

A. 3

B. 6

C. 8

D. 5

Solution

1. Step 1: Calculate base complexity and multipliers

   Base complexity is 2. The multiplier is the argument "first" with value 3, so multiply 2 * 3 = 6.

2. Step 2: Add cost of requested fields

   Fields id and name each cost 1, total 2. Add to 6 gives 8.

3. Final Answer:

   8 -> Option C

4. Quick Check:

   2 * 3 + 1 + 1 = 8 [OK]

Hint: Multiply complexity by argument, then add field costs [OK]

Common Mistakes:

• Ignoring multipliers
• Not adding field costs
• Multiplying fields cost instead of adding

4. Consider this incorrect directive usage:

type Query {
  posts: [Post] @cost(complexity: "high")
}

What is the main error here?

medium

A. The complexity value must be an integer, not a string

B. The field name posts is invalid

C. The directive @cost cannot be used on lists

D. The directive syntax is missing parentheses

Solution

1. Step 1: Check the type of complexity argument

   The complexity argument expects an integer value, but "high" is a string.

2. Step 2: Verify other parts of the directive usage

   The field name and directive usage are valid; parentheses are present.

3. Final Answer:

   The complexity value must be an integer, not a string -> Option A

4. Quick Check:

   Complexity expects integer = D [OK]

Hint: Complexity must be a number, not text [OK]

Common Mistakes:

• Using string instead of integer for complexity
• Thinking directive can't be on lists
• Missing parentheses in directive

5. You have a GraphQL field comments with @cost(complexity: 1, multipliers: ["limit"]). The query requests comments(limit: 4) with subfields text and author, each costing 2. What is the total cost of this query?

hard

A. 12

B. 8

C. 10

D. 6

Solution

1. Step 1: Calculate base complexity with multiplier

   Base complexity is 1. Multiplier is argument "limit" with value 4, so 1 * 4 = 4.

2. Step 2: Add cost of subfields

   Subfields text and author each cost 2, total 4. Add to 4 gives 8.

3. Step 3: Verify the total

   Subfields are added flatly without further multiplication by list size: 4 (base) + 4 (subfields) = 8.

4. Final Answer:

   8 -> Option B

5. Quick Check:

   1*4 + (2+2) = 8 [OK]

Hint: Add base cost times multiplier plus subfields cost [OK]

Common Mistakes:

• Multiplying subfields cost by multiplier (e.g., getting 20)
• Adding costs without multiplier
• Confusing which costs to multiply