PrismaClientKnownRequestError: Unique constraint failed on the fields: (`email`)

You’re trying to insert a duplicate value in a unique column.

Why this happens

Your Prisma schema has a @unique attribute on a field (like email), and you’re attempting to create a record with a value that already exists. This also happens with @@unique compound constraints, or when race conditions cause two concurrent requests to insert the same value before either commits.

Fix 1: Use upsert

await prisma.user.upsert({
  where: { email: 'alice@example.com' },
  update: { name: 'Alice Updated' },
  create: { email: 'alice@example.com', name: 'Alice' },
});

Fix 2: Check before inserting

const existing = await prisma.user.findUnique({
  where: { email: 'alice@example.com' },
});
if (!existing) {
  await prisma.user.create({ data: { email: 'alice@example.com', name: 'Alice' } });
}

Fix 3: Handle the error

try {
  await prisma.user.create({ data });
} catch (e) {
  if (e.code === 'P2002') {
    console.log('Email already exists');
  }
}

Alternative solution: Use createMany with skipDuplicates

When inserting multiple records, skip duplicates silently:

await prisma.user.createMany({
  data: users,
  skipDuplicates: true,
});

Prevention

• Validate uniqueness on the frontend before submitting (e.g., check if email is taken during registration).
• Always handle P2002 errors in your API layer and return a user-friendly 409 Conflict response.

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