graphql

Add a DataLoader per database or service boundary, constructed per request and placed on the context. Each batch function must return exactly keys.length values in the same order as keys, using null or an Error for misses. Batch list relationships into one grouped query keyed by parent id.

Use the Relay cursor Connection shape: edges with node and cursor, pageInfo with hasNextPage and endCursor, and first/after plus last/before arguments. Cursors must be opaque and encode the sort key plus a unique tiebreaker, with a default and server-enforced maximum page size.

An execution error at a non-null position propagates to its parent, and if every position from the root to the failure is non-null the entire data entry becomes null. Fix it by making positions that can fail independently nullable rather than adding try/catch in resolvers.

Yoga masks unexpected errors to 'Unexpected error.' by default and requires throwing GraphQLError for intended messages. Apollo Server passes messages through and includes stack traces unless NODE_ENV is production or test, so masking must be implemented via formatError.

Classify each change as additive or breaking, then use the additive equivalent: add a new field beside the old one, deprecate the old with a reason naming the replacement, and remove only after measured per-field usage reaches zero. Gate every change with a graphql-inspector diff.

Federation is infrastructure requiring a gateway, schema registry, and composition in CI. A single graph contributed to by multiple teams through one repository is a legitimate destination; federate only when team boundaries force it, not by default.