Field-level errors in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Identify the field-level error in this GraphQL query response

Given this GraphQL query response, which field contains an error?

{
  "data": {
    "user": {
      "id": "123",
      "email": null,
      "name": "Alice"
    }
  },
  "errors": [
    {
      "message": "Email not found",
      "path": ["user", "email"]
    }
  ]
}

A There are no field-level errors in this response

B The 'id' field has an error because it is missing

C The 'email' field has an error because it is null and reported in errors

D The 'name' field has an error because it is a string

💡 Hint

Look at the 'errors' array and see which field path it points to.

The 'errors' array shows an error message for the 'email' field. The 'email' field is null, indicating a field-level error.

🧠 Conceptual

intermediate

Understanding field-level errors in GraphQL

What does a field-level error in a GraphQL response mean?

A Only a specific field failed, but other data is returned successfully

B The client sent an invalid authentication token

C The server did not understand the query syntax

D The entire query failed and no data is returned

💡 Hint

Field-level errors allow partial data with some fields failing.

Field-level errors mean that some fields in the response failed, but the rest of the data is still returned.

📝 Syntax

advanced

Which GraphQL error response is correctly formatted for a field-level error?

Choose the valid GraphQL error response that shows a field-level error for the 'price' field.

A { "data": { "product": { "price": 100 } }, "errors": [{ "message": "Price error" }] }

B { "data": { "product": { "price": null } }, "errors": [{ "message": "Price not available", "path": ["product", "price"] }] }

C { "data": null, "errors": [{ "message": "Price not available" }] }

D { "error": "Price field missing" }

💡 Hint

Field-level errors include a 'path' to the field and partial data.

Option B shows partial data with 'price' null and an error message with a path to 'price', which is the correct format for field-level errors.

🔧 Debug

advanced

Find the mistake causing the field-level error in this GraphQL schema snippet

Given this GraphQL schema snippet, why might the 'email' field cause a field-level error?

type User {
  id: ID!
  name: String!
  email: String
}

query {
  user(id: "1") {
    id
    name
    email
  }
}

A The 'email' field is non-nullable but the resolver returns null

B The 'id' field is not defined in the schema

C The 'name' field is missing in the query causing the error

D The 'email' field is nullable but the resolver returns null without error handling

💡 Hint

Nullable fields can return null but may cause errors if not handled properly.

The 'email' field is nullable, so it can be null. If the resolver returns null due to an error but does not handle it, a field-level error can appear.

❓ optimization

expert

How to minimize field-level errors in a complex GraphQL query?

You have a complex GraphQL query fetching multiple nested fields. Which approach best reduces field-level errors?

A Implement detailed error handling in each resolver to return partial data and clear error messages

B Remove all nullable fields from the schema to avoid nulls in responses

C Use error masking to hide all errors and always return null for failed fields

D Disable error reporting in the GraphQL server to prevent errors from reaching clients

💡 Hint

Good error handling helps clients understand and handle partial failures.

Implementing detailed error handling in resolvers allows returning partial data with clear error messages, minimizing unexpected field-level errors.