Optional Field Control

Configure how optional Prisma fields are validated using different Zod patterns.

Use Cases

API with Null Values

When your API accepts explicit null values alongside undefined/omitted fields:

generator zod {
  provider = "prisma-zod-generator"
  optionalFieldBehavior = "nullish"  # default
}

model User {
  id   Int     @id
  name String?
  bio  String?
}

Generated schema accepts all these patterns:

// All valid
{ id: 1, name: "John", bio: "Developer" }
{ id: 1, name: null, bio: undefined }
{ id: 1 } // name and bio omitted

Strict No-Null API

When you want to reject explicit null values:

generator zod {
  provider = "prisma-zod-generator"
  optionalFieldBehavior = "optional"
}

Generated validation:

// Valid
{ id: 1, name: "John" }
{ id: 1 } // name omitted

// Invalid - null rejected
{ id: 1, name: null } // ❌ Validation error

Always-Present Fields

When optional fields must always be included in requests:

generator zod {
  provider = "prisma-zod-generator"
  optionalFieldBehavior = "nullable"
}

Generated validation:

// Valid
{ id: 1, name: "John", bio: "Developer" }
{ id: 1, name: null, bio: null }

// Invalid - fields must be present
{ id: 1 } // ❌ Missing name and bio

Configuration Options

Generator Block

generator zod {
  provider = "prisma-zod-generator"
  optionalFieldBehavior = "nullish" | "optional" | "nullable"
}

JSON Config

{
  "optionalFieldBehavior": "nullish"
}

Comparison Table

Behavior	Zod Output	Accepts undefined	Accepts null	Allows Omitted
nullish	.nullish()	✅	✅	✅
optional	.optional()	✅	❌	✅
nullable	.nullable()	❌	✅	❌

Migration Example

Changing from the legacy .optional().nullable() pattern:

Before:

// Legacy behavior (equivalent to nullish)
name: z.string().optional().nullable();

After with explicit configuration:

// With optionalFieldBehavior = "nullish"
name: z.string().nullish();

// With optionalFieldBehavior = "optional"
name: z.string().optional();

// With optionalFieldBehavior = "nullable"
name: z.string().nullable();

Type Safety

All behaviors maintain compatibility with Prisma types:

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

// Prisma type: { name?: string | null }
const data: Prisma.UserCreateInput = {
  id: 1,
  name: null, // Prisma allows null
};

// All optionalFieldBehavior settings accept this
UserCreateInputSchema.parse(data); // ✅ Always works