gh-djankies-claude-configs-prisma-6/skills/optimizing-query-selection/references/n-plus-one-prevention.md

N+1 Prevention Guide

Anti-Patterns

Over-fetching

Problem:

const user = await prisma.user.findUnique({
  where: { id },
  include: {
    posts: {
      include: {
        comments: {
          include: {
            author: true,
          },
        },
      },
    },
  },
})

Issue: Fetches thousands of records, massive data transfer

Fix: Use select with limits

const user = await prisma.user.findUnique({
  where: { id },
  select: {
    id: true,
    name: true,
    posts: {
      select: {
        id: true,
        title: true,
        _count: {
          select: {
            comments: true,
          },
        },
      },
      take: 10,
      orderBy: {
        createdAt: 'desc',
      },
    },
  },
})

Inconsistent Selection

Problem:

const posts = await prisma.post.findMany({
  include: {
    author: true,
  },
})

Issue: Full author object when only name needed

Fix: Select specific fields

const posts = await prisma.post.findMany({
  select: {
    id: true,
    title: true,
    author: {
      select: {
        name: true,
      },
    },
  },
})

Selecting Then Filtering

Problem:

const users = await prisma.user.findMany()
const activeUsers = users.filter(u => u.status === 'active')

Issue: Fetches all users, filters in application

Fix: Filter in database

const activeUsers = await prisma.user.findMany({
  where: { status: 'active' },
  select: {
    id: true,
    name: true,
    email: true,
  },
})

Prevention Strategies

1. Always load relations upfront - Never query in loops
2. Use select with relations - Don't fetch unnecessary fields
3. Add take limits - Prevent accidental bulk loads
4. Use _count - Don't load relations just to count
5. Test with realistic data - N+1 only shows at scale