Documentation (v4.2.1)

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. Type Provider packages follow a @fastify/type-provider-{provider-name} naming convention.

The following inference packages are supported:

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']
        }
    } as const // don't forget to use const !

}, (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.

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' }
          },
        } as const
      }
    }, (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 bellow:

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

const server = Fastify({
    ajv: {
        customOptions: {
            strict: 'log',
            keywords: ['kind', 'modifier'],
        },
    },
}).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 works! 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({
    ajv: {
        customOptions: {
            strict: 'log',
            keywords: ['kind', 'modifier'],
        },
    },
}).withTypeProvider<TypeBoxTypeProvider>()

registerRoutes(server)

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

type FastifyTypebox = FastifyInstance<
  RawServerDefault,
  RawRequestDefaultExpression<RawServerDefault>,
  RawReplyDefaultExpression<RawServerDefault>,
  FastifyLoggerInstance,
  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
  });
}