Input validation patterns in GraphQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a GraphQL input type with a required string field.

GraphQL

input UserInput {
  name: [1]!
}

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

ABoolean

BInt

CFloat

DString

Attempts:

3 left

💡 Hint

Common Mistakes

Using Int or Boolean for a text field.

Forgetting the exclamation mark to make the field required.

The name field should be of type String and required, so we use String!.

2fill in blank

medium

Complete the code to add an optional integer field for age in the input type.

GraphQL

input UserInput {
  age: [1]
}

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

AFloat!

BInt

CBoolean!

DString!

Attempts:

3 left

💡 Hint

Common Mistakes

Adding an exclamation mark making the field required when it should be optional.

Using String instead of Int for numbers.

The age field should be an optional integer, so use Int without an exclamation mark.

3fill in blank

hard

Fix the error in the input type by choosing the correct scalar type for a boolean field.

GraphQL

input UserInput {
  isActive: [1]!
}

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

ABoolean

BInt

CFloat

DString

Attempts:

3 left

💡 Hint

Common Mistakes

Using String or Int for boolean fields.

Forgetting the exclamation mark for required fields.

The isActive field is a boolean, so it must use the Boolean scalar type with an exclamation mark to be required.

4fill in blank

hard

Fill both blanks to create an input type with a required email string and an optional age integer.

GraphQL

input UserInput {
  email: [1]!
  age: [2]
}

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

AString

BInt!

CInt

DBoolean

Attempts:

3 left

💡 Hint

Common Mistakes

Making the age field required by adding !.

Using Boolean for email or age fields.

The email field is a required string, so use String!. The age field is an optional integer, so use Int without !.

5fill in blank

hard

Fill all three blanks to define an input type with a required username string, an optional age integer, and a required active boolean.

GraphQL

input UserInput {
  username: [1]!
  age: [2]
  active: [3]!
}

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

AString

BInt

CBoolean

DFloat

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to add ! for required fields.

Using wrong scalar types for fields.

The username is a required string (String!), age is an optional integer (Int), and active is a required boolean (Boolean!).

Practice

1. What is the main purpose of input validation in GraphQL schemas?

easy

A. To ensure data is safe and correct before processing

B. To speed up query execution

C. To automatically generate UI forms

D. To store data in multiple databases

Solution

1. Step 1: Understand input validation role

   Input validation checks data before it is saved or used to avoid errors or security issues.

2. Step 2: Identify main goal in GraphQL

   GraphQL uses input validation to keep data safe and correct before processing.

3. Final Answer:

   To ensure data is safe and correct before processing -> Option A

4. Quick Check:

   Input validation = data safety and correctness [OK]

Hint: Input validation means checking data before use [OK]

Common Mistakes:

• Confusing validation with performance optimization
• Thinking validation auto-generates UI
• Assuming validation stores data

2. Which of the following is a valid way to enforce input validation in a GraphQL schema?

easy

A. Using HTML tags in schema definitions

B. Writing SQL queries inside the schema

C. Adding CSS styles to input fields

D. Using custom scalar types for specific formats

Solution

1. Step 1: Review GraphQL schema capabilities

   GraphQL schemas can define custom scalar types to validate formats like email or date.

2. Step 2: Eliminate invalid options

   SQL queries, CSS, and HTML are unrelated to schema validation.

3. Final Answer:

   Using custom scalar types for specific formats -> Option D

4. Quick Check:

   Custom scalars = validation in schema [OK]

Hint: Custom scalars validate input formats in GraphQL [OK]

Common Mistakes:

• Confusing schema with UI styling
• Trying to embed SQL in schema
• Using HTML tags in schema definitions

3. Given this GraphQL input type and resolver snippet, what happens if the input 'username' is an empty string?

input UserInput {
  username: String!
}

resolver createUser(input: UserInput) {
  if (input.username.length === 0) {
    throw new Error('Username cannot be empty');
  }
  return saveUser(input);
}

medium

A. The resolver ignores the username field

B. The resolver throws an error and user is not saved

C. The user is saved with an empty username

D. The schema rejects the query before resolver runs

Solution

1. Step 1: Analyze resolver input check

   The resolver checks if username length is zero and throws an error if true.

2. Step 2: Understand effect of empty string input

   Empty string triggers the error, so user is not saved.

3. Final Answer:

   The resolver throws an error and user is not saved -> Option B

4. Quick Check:

   Empty username triggers error in resolver [OK]

Hint: Empty string triggers error in resolver check [OK]

Common Mistakes:

• Assuming schema rejects empty string automatically
• Thinking empty username is saved
• Ignoring resolver error handling

4. Identify the error in this GraphQL input validation snippet:

input ProductInput {
  price: Float!
}

resolver addProduct(input: ProductInput) {
  if (input.price < 0) {
    return 'Price must be positive';
  }
  saveProduct(input);
  return 'Product added';
}

medium

A. Returning a string error instead of throwing an error

B. Missing input type declaration

C. Using Float instead of Int for price

D. No validation for price being zero

Solution

1. Step 1: Check error handling in resolver

   The resolver returns a string on error instead of throwing an error, which may not stop execution properly.

2. Step 2: Understand proper error signaling

   Throwing an error is standard to halt processing and signal failure in GraphQL.

3. Final Answer:

   Returning a string error instead of throwing an error -> Option A

4. Quick Check:

   Errors should be thrown, not returned as strings [OK]

Hint: Throw errors, don't return error strings in resolvers [OK]

Common Mistakes:

• Returning error messages instead of throwing
• Confusing Float and Int types
• Ignoring zero price validation

5. You want to enforce that a user's email input is always lowercase and matches a valid email format in GraphQL. Which combination is the best approach?

hard

A. Use a directive to reject any uppercase letters without transformation

B. Only rely on GraphQL's String type without extra checks

C. Use a custom scalar for email format and transform input to lowercase in resolver

D. Validate email format in the database after saving

Solution

1. Step 1: Understand validation needs

   Email must be valid format and lowercase before saving or processing.

2. Step 2: Choose best GraphQL validation method

   Custom scalar can enforce format; resolver can transform input to lowercase.

3. Step 3: Evaluate other options

   Relying only on String misses validation; directives alone can't transform; database validation is late.

4. Final Answer:

   Use a custom scalar for email format and transform input to lowercase in resolver -> Option C

5. Quick Check:

   Custom scalar + resolver transform = best validation [OK]

Hint: Combine custom scalar and resolver for format and case [OK]

Common Mistakes:

• Skipping format validation
• Expecting directives to transform input
• Validating only after saving data