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GraphQL 19 errors

GraphQL Errors

Validation, depth limits, N+1 queries and fragment problems.

Understanding GraphQL errors

GraphQL returns HTTP 200 with an errors array far more often than it returns a non-2xx status, so clients that only check the status code silently ignore failures. Errors split into validation (the query does not match the schema, always fixable from the schema), authorisation (per-field resolvers rejecting), and performance guards (depth and complexity limits) which exist to protect the server from expensive queries.

How to debug GraphQL errors

  1. Always inspect the errors array, not just the HTTP status. Each entry carries a path that points at the exact field that failed.
  2. Validate the query against the schema locally before sending it. GraphQL IDEs and graphql-codegen catch every validation error at build time.
  3. For N+1 problems, enable resolver tracing or SQL logging and count queries per request. A DataLoader that batches by key is the standard fix.
  4. When you hit a depth or complexity limit, restructure the query rather than raising the limit. The limit is usually protecting the database from an unbounded traversal.
  5. Check whether the error is from the gateway or the subgraph in a federated setup; the two have separate schemas and separate authorisation.

Tools worth reaching for

  • GraphiQL / Apollo Sandbox
  • graphql-codegen
  • Apollo tracing
  • DataLoader

All 19 GraphQL errors

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