Validation errors in GraphQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all columns from the table named 'users'.

GraphQL

SELECT [1] FROM users;

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

Aeverything

Ball

Ccolumns

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using words like 'all' or 'columns' instead of '*'

Leaving the blank empty

The asterisk (*) is used in SQL to select all columns from a table.

2fill in blank

medium

Complete the code to filter rows where the age is greater than 30.

GraphQL

SELECT * FROM employees WHERE age [1] 30;

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

A<

B=

C>

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' which checks for equality

Using '<' which checks for less than

The '>' operator filters rows where the age is greater than 30.

3fill in blank

hard

Fix the error in the SQL query to count the number of orders.

GraphQL

SELECT COUNT([1]) FROM orders;

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

Acount

B*

Corders

Dorder_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using a column name that might have NULL values

Using the table name inside COUNT

Using COUNT(*) counts all rows in the table, which is the correct way to count orders.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps words to their lengths only if length is greater than 3.

GraphQL

{word: [1] for word in words if [2](word) > 3}

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

Alen(word)

Bword

Clen

Dword.length

Attempts:

3 left

💡 Hint

Common Mistakes

Using word.length which is not valid in Python

Using word instead of its length in the dictionary value

The dictionary comprehension maps each word to its length using len(word), and filters words where len(word) is greater than 3.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps uppercase keys to values only if value is greater than 0.

GraphQL

result = {{ [1]: [2] for k, v in data.items() if v [3] 0 }}

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

Ak.upper()

Bv

C>

Dk

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'k' instead of 'k.upper()' for keys

Using '<' instead of '>' in the condition

The comprehension maps uppercase keys (k.upper()) to their values (v) only if the value is greater than 0.

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