Relations in Prisma in NestJS - Performance & Optimization

Performance: Relations in Prisma

MEDIUM IMPACT

This affects database query speed and server response time when fetching related data.

Fetching related data with Prisma relations

NestJS

const users = await prisma.user.findMany({ include: { posts: true } });

Fetches users and their posts in a single query, reducing database calls.

📈 Performance GainSingle database query regardless of number of users, greatly improving response time.

Fetching related data with Prisma relations

NestJS

const users = await prisma.user.findMany();
for (const user of users) {
  user.posts = await prisma.post.findMany({ where: { authorId: user.id } });
}

This triggers one query per user, causing many database calls and slow response.

📉 Performance CostTriggers N database queries for N users, increasing server response time linearly.

Performance Comparison

Pattern	Database Queries	Server Response Time	Client Impact	Verdict
N+1 Query Pattern	N+1 queries	High latency	Slow interaction response	[X] Bad
Single Query with include	1 query	Low latency	Fast interaction response	[OK] Good

Rendering Pipeline

Relations in Prisma affect the server-side data fetching stage before rendering. Efficient queries reduce server processing time and speed up data delivery to the frontend.

→Data Fetching

→Server Response

→Client Rendering

⚠️ BottleneckMultiple database queries increase server response time and delay rendering.

Core Web Vital Affected

INP

This affects database query speed and server response time when fetching related data.

Optimization Tips

1Avoid fetching related data inside loops to prevent many database queries.

2Use Prisma's include or select to fetch relations in a single query.

3Reducing database queries improves server response and user interaction speed.

Performance Quiz - 3 Questions

What is the main performance issue with fetching related data in a loop with Prisma?

A It causes many database queries, increasing server response time.

B It reduces database queries to one, improving speed.

C It caches data on the client side automatically.

D It improves browser rendering speed.

DevTools: Network

How to check: Open DevTools, go to Network tab, filter XHR requests, and observe the number of API calls made when loading related data.

What to look for: Multiple repeated API calls indicate N+1 query problem; a single call with all data is optimal.