Using Type.Module with fastify addSchema

[iamchathu]

export const customerSchemaModule = Type.Module({
    Customer: Type.Object(
        {
            customerId: Type.String({
                format: 'uuid',
                description: 'Customer ID',
            }),
            name: Type.String({
                minLength: 3,
                description: 'Customer name',
                examples: ['John Doe'],
            }),
        },
        {
            additionalProperties: false,
            $id: 'Customer',
            description: 'A customer object',
        },
    ),

  ...
});

---

fastify.addSchema(customerSchemaModule.Import('Customer'));

Is throwing an error

/.pnpm/fastify@5.3.3/node_modules/fastify/lib/schemas.js:29
    throw new FST_ERR_SCH_MISSING_ID()
    ^
FastifyError [Error]: Missing schema $id property

[potatohoney-p]

The $id: 'Customer' is inside the imported schema's $defs.Customer. The object returned by Import('Customer') has $defs and $ref, but no root $id, which is what Fastify's addSchema() checks. See the TypeBox import implementation and Fastify's check.

For your existing module, add a distinct ID to the imported wrapper, preserving its definitions and reference:

fastify.addSchema({
  ...customerSchemaModule.Import('Customer'),
  $id: 'CustomerApi',
});

fastify.post('/customers', {
  schema: {
    body: { $ref: 'CustomerApi#' },
    response: {
      200: { $ref: 'CustomerApi#' },
    },
  },
}, async (request) => request.body);

CustomerApi identifies the wrapper; Customer still identifies the definition inside it. Don't reuse Customer as the wrapper ID: that collides with the existing definition when Fastify compiles the route. This follows Fastify's shared-schema reference pattern.

Also, Import('Customer', { $id: 'CustomerApi' }) does not set the wrapper's ID in 0.34.x: those options apply to the imported definition instead.

Verified with Fastify 5.3.3 and @sinclair/typebox 0.34.33 / 0.34.52, using Fastify's default validator and serializer: valid requests return 200, invalid UUIDs/short names return 400, and references to another definition in the same module work for both nested request validation and response serialization. The same tests pass with Fastify 5.11.0 and TypeBox 0.34.52.

This addresses the Type.Module API in @sinclair/typebox 0.34.x; the newer typebox package has a different API.