Input validation patterns in GraphQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is input validation in GraphQL?

Input validation in GraphQL means checking the data sent by users to make sure it is correct and safe before using it in the system.

beginner

Why is input validation important in GraphQL APIs?

It helps prevent errors and security problems by making sure only valid and expected data is accepted.

intermediate

Name a common pattern to validate inputs in GraphQL schemas.

Using custom scalar types or input types with specific fields and constraints to check data format and values.

intermediate

How can you validate an email input in GraphQL?

Create a custom scalar type for email that checks the string matches an email pattern before accepting it.

intermediate

What role do resolver functions play in input validation?

Resolvers can add extra checks on inputs before processing, ensuring data meets business rules beyond schema validation.

What is the first step in input validation in GraphQL?

A Design UI forms

B Define input types with constraints

C Create database tables

D Write resolver functions

Defining input types with constraints helps GraphQL check inputs automatically.

Which GraphQL feature helps enforce input formats like email or date?

A Directives

B Fragments

C Subscriptions

D Custom scalar types

Custom scalar types allow defining specific validation rules for inputs like email or date.

Where can you add extra input validation beyond schema checks?

A In resolver functions

B In the database only

C In the client UI only

D In GraphQL queries

Resolvers can perform additional validation before processing data.

What happens if input validation fails in GraphQL?

A The query returns an error

B The query runs anyway

C The server crashes

D The input is ignored silently

GraphQL returns an error when input validation fails to prevent bad data.

Which is NOT a good practice for input validation in GraphQL?

A Validate inputs in schema and resolvers

B Use custom scalars for special formats

C Trust all client inputs without checks

D Return clear error messages on invalid input

Trusting client inputs without validation is unsafe and not recommended.

Explain how input validation works in GraphQL and why it is important.

Think about how GraphQL schema helps check data.

Describe two ways to implement input validation in a GraphQL API.

Consider schema design and resolver roles.

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