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Pascual Vila

Frontend Instructor // Code Syllabus

Common Pitfalls & Errors

The Error //

Opening a new database connection inside the context function on every request

// Wrong: opens a brand new connection on every request
context: () => ({ models: connectToDatabase() })

// Correct: connect once at startup, reuse the same models in every request
const models = await connectToDatabase();
const server = new ApolloServer({ typeDefs, resolvers, context: () => ({ models }) });

The Solution //

Apollo Server calls the context function once per incoming request. If context: () => ({ models: connectToDatabase() }) actually opens a fresh connection each time instead of reusing an existing pool, the database gets hammered with new connection overhead on every single GraphQL request, quickly exhausting the connection limit under real traffic. Initialize the database connection/pool once at server startup, and only pass the already-connected models into context.

The Error //

Forgetting to return the Promise from a resolver

// Wrong: DB call happens but its result is discarded
getUser: (parent, { id }, { models }) => {
  models.User.findById(id); // missing 'return'
}

// Correct
getUser: (parent, { id }, { models }) => {
  return models.User.findById(id);
}

The Solution //

A resolver that calls an async database method but doesn't return its result (or forgets 'return' in a block-bodied arrow function) leaves GraphQL with nothing to await — the field resolves to null or undefined even though the database call actually succeeded. Every resolver must explicitly return the value or Promise it produces.