Validation errors in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What error occurs with missing required field?

Given this GraphQL schema snippet:

type User { id: ID! name: String! age: Int }

What error will occur if you run this query?

{ user { id age } }

GraphQL

{ user { id age } }

A Field 'age' does not exist on type 'User'.

B Syntax error: Unexpected token 'user'.

C No error, query runs successfully.

D Field 'name' of required type 'String!' was not provided.

💡 Hint

Non-nullable fields (!) do not need to be selected in the query.

No validation error occurs. GraphQL does not require selecting all fields from an object type, even non-nullable ones. The non-null constraint is enforced during field resolution if the resolver returns null.

📝 Syntax

intermediate

Identify the syntax error in this GraphQL query

What is the syntax error in this query?

{ user(id: 1) { id name age } 

GraphQL

{ user(id: 1) { id name age } 

A Invalid argument type for 'id', should be a string.

B Missing closing brace '}' at the end of the query.

C Field 'age' is not defined in the schema.

D Extra comma after 'name' field.

💡 Hint

Count the opening and closing braces.

The query is missing the final closing brace '}', causing a syntax error.

🔧 Debug

advanced

Why does this query fail with 'Unknown argument' error?

Given the schema:

type Query { user(id: ID!): User }

Why does this query fail?

{ user(userId: "123") { id name } }

GraphQL

{ user(userId: "123") { id name } }

A Argument name 'userId' does not match the schema, should be 'id'.

B ID argument must be an integer, not a string.

C Field 'name' is not defined in 'User' type.

D Query is missing required field 'user'.

💡 Hint

Check argument names carefully against the schema.

The schema expects argument 'id' but the query uses 'userId', causing an unknown argument error.

🧠 Conceptual

advanced

What causes a 'Field cannot be queried on type' error?

If you get an error saying a field cannot be queried on a type, what is the most likely cause?

A The query is missing a required argument.

B The query has a syntax error.

C The field is deprecated but still queryable.

D The field is not defined in the schema for that type.

💡 Hint

Think about schema definitions and allowed fields.

This error means the field does not exist on the specified type in the schema.

❓ optimization

expert

How to fix 'Variable "$id" of required type "ID!" was not provided' error?

Given this query:

query getUser($id: ID!) { user(id: $id) { id name } }

And this variables object:

{}

What is the best way to fix the error?

A Provide a value for the variable 'id' in the variables object.

B Remove the exclamation mark from 'ID!' in the query.

C Remove the variable and hardcode the id value in the query.

D Change the variable type to 'ID' without exclamation mark.

💡 Hint

Required variables must be given values when executing queries.

The error occurs because the required variable 'id' is missing a value.

Practice

1. What does a validation error in GraphQL indicate?

easy

A. The data returned is empty

B. The query has a mistake and cannot run correctly

C. The server is down and cannot respond

D. The query executed successfully

Solution

1. Step 1: Understand the purpose of validation errors

   Validation errors occur when the GraphQL query has syntax or structure mistakes.

2. Step 2: Identify what validation errors prevent

   They stop the query from running and returning data until fixed.

3. Final Answer:

   The query has a mistake and cannot run correctly -> Option B

4. Quick Check:

   Validation error = query mistake [OK]

Hint: Validation errors mean query mistakes, not server or data issues [OK]

Common Mistakes:

• Confusing validation errors with server errors
• Thinking validation errors mean empty data
• Assuming validation errors mean success

2. Which of the following is a correct way to handle validation errors in a GraphQL query?

easy

A. Ignore errors and use the data anyway

B. Delete the database to remove errors

C. Check the error messages and fix the query syntax

D. Restart the server to clear errors

Solution

1. Step 1: Identify proper error handling

   Validation errors require checking messages to understand what is wrong in the query.

2. Step 2: Fix the query syntax based on error details

   Correcting the query syntax resolves validation errors so the query can run.

3. Final Answer:

   Check the error messages and fix the query syntax -> Option C

4. Quick Check:

   Fix syntax after error check = correct handling [OK]

Hint: Fix query syntax after reading error messages [OK]

Common Mistakes:

• Ignoring errors and using bad data
• Restarting server does not fix query errors
• Deleting database is unrelated to validation errors

3. Given this GraphQL query snippet:
{ user(id: 1) { name age } }
If the schema does not define an age field for user, what validation error will occur?

medium

A. "Field 'age' is not defined on type 'User'"

B. "Syntax error near 'user'"

C. "Missing required argument 'id'"

D. "Server timeout error"

Solution

1. Step 1: Check the query fields against schema

   The query asks for age on user, but schema lacks this field.

2. Step 2: Identify the validation error message

   GraphQL reports that the field is not defined on the type.

3. Final Answer:

   "Field 'age' is not defined on type 'User'" -> Option A

4. Quick Check:

   Undefined field error = "Field 'age' is not defined on type 'User'" [OK]

Hint: Check if requested fields exist in schema [OK]

Common Mistakes:

• Confusing syntax errors with missing fields
• Assuming missing arguments cause this error
• Thinking server errors are validation errors

4. You wrote this GraphQL query:
{ product(id: ) { name price } }
It causes a validation error. What is the main problem?

medium

A. Missing value for the argument id

B. Incorrect field names name and price

C. Extra brackets around the query

D. No query operation keyword like query

Solution

1. Step 1: Inspect the argument syntax

   The argument id is empty; it needs a value like a number or string.

2. Step 2: Understand validation error cause

   GraphQL requires argument values; missing values cause syntax validation errors.

3. Final Answer:

   Missing value for the argument id -> Option A

4. Quick Check:

   Empty argument value causes validation error [OK]

Hint: Always provide values for required arguments [OK]

Common Mistakes:

• Thinking field names cause error here
• Assuming brackets are extra
• Believing 'query' keyword is mandatory

5. You want to query a list of books with optional filtering by author name. Your query is:

{ books(author: "Alice") { title author } }

But the schema defines author as a non-nullable field in Book, not as an argument for books. What validation error will you get?

hard

A. "Invalid query operation"

B. "Field 'author' must not be null"

C. "Missing required field 'title'"

D. "Unknown argument 'author' on field 'books'"

Solution

1. Step 1: Analyze the query arguments vs schema

   The query uses author as an argument to books, but schema does not allow this argument.

2. Step 2: Identify the validation error message

   GraphQL reports unknown argument errors when arguments are not defined on fields.

3. Final Answer:

   "Unknown argument 'author' on field 'books'" -> Option D

4. Quick Check:

   Invalid argument name causes unknown argument error [OK]

Hint: Check if arguments exist on queried fields in schema [OK]

Common Mistakes:

• Confusing field nullability with argument errors
• Assuming missing fields cause this error
• Thinking query operation keyword is missing