Orm N Plus One Query (ARCH3079)

Key typescript.performance.orm-n-plus-one · Severity error · Category performance

Retired

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Iterating a query result and lazily accessing each item’s related record triggers a separate database query per iteration (N+1). Relationships should be eager-loaded.

Incorrect

const orders = await repo.find({ where: { active: true } });
for (const order of orders) {
  console.log(order.customer.name); // lazy query per iteration
}

Correct

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

Fix

Eager-load related data in a single query with relations / an eager join before the loop.