N+1 Query

Database calls inside loops

warningPerformanceno-n-plus-one

Why this matters

A database query inside a loop makes N+1 round trips to the database. For 100 items, that's 101 queries instead of 1. Response times grow linearly with data size.

✗ Bad

const posts = await db.post.findMany();
for (const post of posts) {
  // One query per post — N+1!
  const author = await db.user.findUnique({
    where: { id: post.authorId },
  });
  post.author = author;
}

✓ Good

const posts = await db.post.findMany({
  include: { author: true },
});
// Single query with JOIN — no N+1

How to fix

Use eager loading (include/join), batch queries (WHERE id IN), or DataLoader to fetch related data in a single query instead of per-item.

All rules