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Version: v4.28.x

Type-Providers

Type Providers​

Type Providers are a TypeScript only feature that enables Fastify to statically infer type information directly from inline JSON Schema. They are an alternative to specifying generic arguments on routes; and can greatly reduce the need to keep associated types for each schema defined in your project.

Providers​

Type Providers are offered as additional packages you will need to install into your project. Each provider uses a different inference library under the hood; allowing you to select the library most appropriate for your needs. Official Type Provider packages follow a @fastify/type-provider-{provider-name} naming convention, and there are several community ones available as well.

The following inference packages are supported:

See also the Type Provider wrapper packages for each of the packages respectively:

Json Schema to Ts​

The following sets up a json-schema-to-ts Type Provider

$ npm i @fastify/type-provider-json-schema-to-ts
import { JsonSchemaToTsProvider } from '@fastify/type-provider-json-schema-to-ts'

import fastify from 'fastify'

const server = fastify().withTypeProvider<JsonSchemaToTsProvider>()

server.get('/route', {
    schema: {
        querystring: {
            type: 'object',
            properties: {
                foo: { type: 'number' },
                bar: { type: 'string' },
            },
            required: ['foo', 'bar']
        }
    }

}, (request, reply) => {

    // type Query = { foo: number, bar: string }

    const { foo, bar } = request.query // type safe!
})

TypeBox​

The following sets up a TypeBox Type Provider

$ npm i @fastify/type-provider-typebox
import { TypeBoxTypeProvider } from '@fastify/type-provider-typebox'
import { Type } from '@sinclair/typebox'

import fastify from 'fastify'

const server = fastify().withTypeProvider<TypeBoxTypeProvider>()

server.get('/route', {
    schema: {
        querystring: Type.Object({
            foo: Type.Number(),
            bar: Type.String()
        })
    }
}, (request, reply) => {

    // type Query = { foo: number, bar: string }

    const { foo, bar } = request.query // type safe!
})

See also the TypeBox documentation on how to set up AJV to work with TypeBox.

Zod​

See official documentation for Zod type provider instructions.

Scoped Type-Provider​

The provider types don't propagate globally. In encapsulated usage, one can remap the context to use one or more providers (for example, typebox and json-schema-to-ts can be used in the same application).

Example:

import Fastify from 'fastify'
import { TypeBoxTypeProvider } from '@fastify/type-provider-typebox'
import { JsonSchemaToTsProvider } from '@fastify/type-provider-json-schema-to-ts'
import { Type } from '@sinclair/typebox'

const fastify = Fastify()

function pluginWithTypebox(fastify: FastifyInstance, _opts, done): void {
  fastify.withTypeProvider<TypeBoxTypeProvider>()
    .get('/', {
      schema: {
        body: Type.Object({
          x: Type.String(),
          y: Type.Number(),
          z: Type.Boolean()
        })
      }
    }, (req) => {
        const { x, y, z } = req.body // type safe
    });
  done()
}

function pluginWithJsonSchema(fastify: FastifyInstance, _opts, done): void {
  fastify.withTypeProvider<JsonSchemaToTsProvider>()
    .get('/', {
      schema: {
        body: {
          type: 'object',
          properties: {
            x: { type: 'string' },
            y: { type: 'number' },
            z: { type: 'boolean' }
          },
        }
      }
    }, (req) => {
      const { x, y, z } = req.body // type safe
    });
  done()
}

fastify.register(pluginWithJsonSchema)
fastify.register(pluginWithTypebox)

It's also important to mention that once the types don't propagate globally, currently is not possible to avoid multiple registrations on routes when dealing with several scopes, see below:

import Fastify from 'fastify'
import { TypeBoxTypeProvider } from '@fastify/type-provider-typebox'
import { Type } from '@sinclair/typebox'

const server = Fastify().withTypeProvider<TypeBoxTypeProvider>()

server.register(plugin1) // wrong
server.register(plugin2) // correct

function plugin1(fastify: FastifyInstance, _opts, done): void {
  fastify.get('/', {
    schema: {
      body: Type.Object({
        x: Type.String(),
        y: Type.Number(),
        z: Type.Boolean()
      })
    }
  }, (req) => {
    // it doesn't work! in a new scope needs to call `withTypeProvider` again
    const { x, y, z } = req.body
  });
  done()
}

function plugin2(fastify: FastifyInstance, _opts, done): void {
  const server = fastify.withTypeProvider<TypeBoxTypeProvider>()

  server.get('/', {
    schema: {
      body: Type.Object({
        x: Type.String(),
        y: Type.Number(),
        z: Type.Boolean()
      })
    }
  }, (req) => {
    // works
    const { x, y, z } = req.body
  });
  done()
}

Type Definition of FastifyInstance + TypeProvider​

When working with modules one has to make use of FastifyInstance with Type Provider generics. See the example below:

// index.ts
import Fastify from 'fastify'
import { TypeBoxTypeProvider } from '@fastify/type-provider-typebox'
import { registerRoutes } from './routes'

const server = Fastify().withTypeProvider<TypeBoxTypeProvider>()

registerRoutes(server)

server.listen({ port: 3000 })
// routes.ts
import { Type } from '@sinclair/typebox'
import {
  FastifyInstance,
  FastifyBaseLogger,
  RawReplyDefaultExpression,
  RawRequestDefaultExpression,
  RawServerDefault
} from 'fastify'
import { TypeBoxTypeProvider } from '@fastify/type-provider-typebox'

type FastifyTypebox = FastifyInstance<
  RawServerDefault,
  RawRequestDefaultExpression<RawServerDefault>,
  RawReplyDefaultExpression<RawServerDefault>,
  FastifyBaseLogger,
  TypeBoxTypeProvider
>;

export function registerRoutes(fastify: FastifyTypebox): void {
  fastify.get('/', {
    schema: {
      body: Type.Object({
        x: Type.String(),
        y: Type.Number(),
        z: Type.Boolean()
      })
    }
  }, (req) => {
    // works
    const { x, y, z } = req.body
  });
}