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.