N Plus One Query (ARCH3050)

Key typescript.orm.n-plus-one-query · Severity warning · Category orm

Running a separate query for each element inside a loop produces one list query plus N follow-up queries. This is the classic ORM performance killer; fetch related data in a single round-trip.

Incorrect

const orders = await orderRepo.find();
for (const order of orders) {
  // A separate SELECT per order
  const customer = await customerRepo.findOneBy({ id: order.customerId });
  console.log(customer.name);
}

Correct

const orders = await orderRepo.find({ relations: { customer: true } });
for (const order of orders) {
  console.log(order.customer.name);
}

Fix

Eager-load related data with relations/include and drop the per-iteration queries.