Prisma ORM Error P2002: Unique constraint failed

Identify: does your log match?

PrismaClientKnownRequestError:
Invalid `prisma.user.create()` invocation in
/app/src/routes/signup.ts:18:34

  15 const hash = await argon2.hash(body.password);
  16
  17 // create account
→ 18 const user = await prisma.user.create(
Unique constraint failed on the fields: (`email`)
  code: 'P2002',
  meta: { modelName: 'User', target: [ 'email' ] }

1. High

   Duplicate signup or double submit

   The user clicked twice or the client retried after a timeout. The first create already committed the email.

2. Medium

   findFirst then create race

   Two requests both check for an existing row, find none, and both call create. Only the database constraint stops the second.

3. Medium

   Seed script re-run on populated DB

   prisma db seed with create() instead of upsert() fails on the second run.

Fix

const user = await prisma.user.create({ data: { email, name } });
return Response.json(user);

import { Prisma } from '@prisma/client';

try {
  const user = await prisma.user.create({ data: { email, name } });
  return Response.json(user, { status: 201 });
} catch (e) {
  if (e instanceof Prisma.PrismaClientKnownRequestError && e.code === 'P2002') {
    return Response.json({ error: 'Email already registered' }, { status: 409 });
  }
  throw e;
}

Verify: reproduce it on purpose

$ node -e "const {PrismaClient}=require('@prisma/client');const p=new PrismaClient();(async()=>{await p.user.create({data:{email:'dup@x.io'}});await p.user.create({data:{email:'dup@x.io'}})})().catch(e=>console.log(e.code))"

Prevent

• Read e.meta.target to know which field collided.
• Disable the submit button while the request is in flight.
• Prefer upsert in seed scripts.