When handling errors with `whenLoaded()` in GraphQL, best practices focus on managing errors effectively within the GraphQL response structure while also addressing deeper relational loading challenges that `whenLoaded()` might present in frameworks like Laravel. Here is a detailed overview of best practices:
Understanding `whenLoaded()` in Context
`whenLoaded()` is typically used in Laravel resources to conditionally include related data only if the relationship is already loaded, avoiding unnecessary database queries. However, it has limitations with nested or deeper-than-one-level relations, which can cause N+1 query problems if not handled carefully[6]. This is relevant because errors can arise when relations are not loaded as expected or when deeper relations cause performance or data consistency issues.
Best Practices for Error Handling with `whenLoaded()` in GraphQL
1. Treat Errors as Part of the Data Schema
- Instead of relying solely on the default GraphQL `errors` array (which is schemaless and can be hard to track), model errors as part of your GraphQL schema using custom error types or interfaces. For example, define an `Error` interface and specific error types like `UserRegisterInvalidInputError` that implement it[1][2].
- This approach allows errors to be returned as part of the query data, enabling clients to handle errors as structured data rather than just messages.
2. Use Response Unions for Error and Success Types
- Return unions of success and error types from resolvers so that clients can distinguish between valid data and error states explicitly. This forces both backend and frontend to handle errors as data, improving scalability and clarity[2].
- For example, a resolver might return either a `User` type or a `UserNotVerifiedError` union member.
3. Provide Clear, Actionable Error Messages
- Ensure error messages are descriptive and instructive, helping clients understand what went wrong and how to resolve it[8].
- Include error `message`, `path`, and `locations` in the GraphQL error response to pinpoint where the error occurred in the query.
4. Use the `extensions` Field for Metadata
- Add structured metadata in the `extensions` field of GraphQL errors, such as error codes, timestamps, or severity levels. This helps clients programmatically handle errors and display appropriate UI feedback[3][8].
5. Gracefully Handle Partial Data with Errors
- GraphQL allows returning partial data alongside errors. Use this feature to deliver as much valid data as possible even if some parts fail (e.g., if a nested relation is not loaded or errors out). This improves user experience by avoiding full query failures[7][8].
- In the context of `whenLoaded()`, if a deeper relation is not loaded and cannot be fetched without causing N+1 problems, consider returning null or a default value with an accompanying error message.
6. Avoid N+1 Query Problems with Conditional Loading
- Since `whenLoaded()` only works on first-level relations, deeper relations should be checked with methods like `relationLoaded` and loaded conditionally using `when` or manual checks to avoid unexpected queries and errors[6].
- This prevents performance issues that can indirectly cause errors due to timeouts or resource limits.
7. Centralize Error Formatting and Logging
- Use server-side error formatting (e.g., Apollo Serverâs `formatError`) to ensure consistent error messages and to omit sensitive information before sending errors to clients[3].
- Log errors centrally to track recurring issues and improve reliability.
8. Document Expected Errors Clearly
- Use schema documentation and custom directives to inform clients about possible errors they might encounter, especially for operations involving conditional or nested relations[8].
Summary
Handling errors with `whenLoaded()` in GraphQL involves combining careful relational data loading strategies with robust GraphQL error handling best practices:
- Model errors as part of your schema using custom types and unions.
- Provide clear error messages and use the `extensions` field for metadata.
- Return partial data with errors to improve resilience.
- Avoid N+1 query problems by conditionally loading deeper relations.
- Centralize error formatting and logging.
- Document expected errors for client developers.
This approach ensures that errors related to conditional data loading with `whenLoaded()` are managed transparently, improving both backend reliability and frontend error handling experience.
Citations:
[1] https://testfully.io/blog/graphql-error-handling/
[2] https://www.reddit.com/r/graphql/comments/q8u69k/question_graphql_error_handling_best_practices/
[3] https://www.apollographql.com/docs/apollo-server/data/errors
[4] https://productionreadygraphql.com/2020-08-01-guide-to-graphql-errors/
[5] https://www.apollographql.com/docs/react/data/error-handling
[6] https://stackoverflow.com/questions/49965081/how-do-i-use-whenloaded-for-deeper-than-one-level-relations
[7] https://itnext.io/the-definitive-guide-to-handling-graphql-errors-e0c58b52b5e1
[8] https://daily.dev/blog/graphql-errors-understanding-the-basics