Services

Services are the heart of every Feathers application. Services are objects or instances of classes that implement certain methods. Feathers itself will also add some additional methods and functionality to its services.

Service methods

Service methods are pre-defined CRUD and custom methods that your service provides or that have already been implemented by one of the database adapters. Below is an example of a Feathers service as a class or object.

import { feathers } from 'feathers'
import type { Application, Params, Id, NullableId } from 'feathers'

class MyServiceClass {
  async find(params: Params) {
    return []
  }
  async get(id: Id, params: Params) {}
  async create(data: any, params: Params) {}
  async update(id: NullableId, data: any, params: Params) {}
  async patch(id: NullableId, data: any, params: Params) {}
  async remove(id: NullableId, params: Params) {}
  async setup(app: Application, path: string) {}
  async teardown(app: Application, path: string) {}
}

const myServiceObject = {
  async find(params: Params) {
    return []
  },
  async get(id: Id, params: Params) {},
  async create(data: any, params: Params) {},
  async update(id: NullableId, data: any, params: Params) {},
  async patch(id: NullableId, data: any, params: Params) {},
  async remove(id: NullableId, params: Params) {},
  async setup(app: Application, path: string) {},
  async teardown(app: Application, path: string) {}
}

type ServiceTypes = {
  'my-service': MyServiceClass
  'my-service-object': typeof myServiceObject
}

const app = feathers<ServiceTypes>()

app.use('my-service', new MyServiceClass())
app.use('my-service-object', myServiceObject)

Service methods must use async/await or return a Promise and can have the following parameters:

• id — The identifier for the resource. A resource is the data identified by a unique id.
• data — The resource data.
• params - Additional parameters for the method call (see params)

Once registered, the service can be retrieved and used via app.service():

const myService = app.service('my-service')

const items = await myService.find()

const item = await app.service('my-service').get(1)

console.log('.get(1)', item)

params

params contain additional information for the service method call. Some properties in params can be set by Feathers already. Commonly used are:

• params.query - the query parameters from the client, passed as URL query parameters (see the HTTP chapter).
• params.route - route placeholder parameters (see HTTP params.route).
• params.provider - The transport (rest) used for this service call. Will be undefined for internal calls from the server (unless passed explicitly).
• params.headers - The HTTP headers connected to this service call if available.
• params.connection - If the service call has been made by a real-time transport (e.g. through SSE), params.connection is the connection object that can be used with channels.

.find(params)

service.find(params) -> Promise - Retrieves a list of all resources from the service. params.query can be used to filter and limit the returned data.

class MessageService {
  async find(params: Params) {
    return [
      {
        id: 1,
        text: 'Message 1'
      },
      {
        id: 2,
        text: 'Message 2'
      }
    ]
  }
}

app.use('messages', new MessageService())

.get(id, params)

service.get(id, params) -> Promise - Retrieves a single resource with the given id from the service.

import type { Id, Params } from 'feathers'

class TodoService {
  async get(id: Id, params: Params) {
    return {
      id,
      text: `You have to do ${id}!`
    }
  }
}

app.use('todos', new TodoService())

.create(data, params)

service.create(data, params) -> Promise - Creates a new resource with data. The method should return with the newly created data. data may also be an array.

A successful create method call emits the created service event with the returned data or a separate event for every item if the returned data is an array.

import type { Params } from 'feathers'

type Message = { text: string }

class MessageService {
  messages: Message[] = []

  async create(data: Message, params: Params) {
    this.messages.push(data)

    return data
  }
}

app.use('messages', new MessageService())

.update(id, data, params)

service.update(id, data, params) -> Promise - Replaces the resource identified by id with data. The method should return with the complete, updated resource data. id can also be null when updating multiple records.

A successful update method call emits the updated service event. If an array is returned, it will send an individual updated event for every item.

.patch(id, data, params)

service.patch(id, data, params) -> Promise - Merges the existing data of the resource identified by id with the new data. id can also be null indicating that multiple resources should be patched with params.query containing the query criteria.

A successful patch method call emits the patched service event with the returned data. When an array is returned when patching multiple items, it will send an individual patched event for every item in the array.

The method should return with the complete, updated resource data. Implement patch additionally (or instead of) update if you want to distinguish between partial and full updates and support the PATCH HTTP method.

.remove(id, params)

service.remove(id, params) -> Promise - Removes the resource with id. The method should return with the removed data. id can also be null, which indicates the deletion of multiple resources, with params.query containing the query criteria.

A successful remove method call emits the removed service event with the returned data or a separate event for every item if the returned data is an array.

.setup(app, path)

service.setup(app, path) -> Promise is a special method that initializes the service, passing an instance of the Feathers application and the path it has been registered on.

When calling app.setup all registered services setup methods will be called. If a service is registered afterwards, the setup method will be called immediately.

.teardown(app, path)

service.teardown(app, path) -> Promise is a special method that shuts down the service, passing an instance of the Feathers application and the path it has been registered on. If a service implements a teardown method, it will be called during app.teardown() or when unregistering the service via app.unuse.

Custom Methods

A custom method is any other service method you want to expose publicly. A custom method must have the signature of (data, params) with the same semantics as standard service methods (data is the payload, params is the service params). They can be used with hooks and must be async or return a Promise.

In order to register a public custom method, the names of all methods have to be passed as the methods option when registering the service with app.use()

import { feathers } from 'feathers'
import type { Id, Params } from 'feathers'

type CustomData = {
  name: string
}

class MyService {
  async get(id: Id, params: Params) {
    return {
      id,
      message: `You have to do ${id}`
    }
  }

  async myCustomMethod(data: CustomData, params: Params) {
    return data
  }
}

type ServiceTypes = {
  'my-service': MyService
}

const app = feathers<ServiceTypes>()

app.use('my-service', new MyService(), {
  // Pass all methods you want to expose
  methods: ['get', 'myCustomMethod']
})

See the HTTP API section on how to use those custom methods via HTTP.

Feathers functionality

When registering a service, Feathers (or its plugins) can also add its own methods to a service. Most notably, every service will automatically become an instance of an EventEmitter.

.hooks(hooks)

Register hooks for this service.

.publish(event, publisher)

Register an event publishing callback. For more information, see the channels chapter.

.on(eventname, listener)

Provided by the EventEmitter .on. Registers a listener method (function(data) {}) for the given eventname.

.emit(eventname, data)

Provided by the EventEmitter .emit. Emits the event eventname to all event listeners.

.removeListener(eventname)

Provided by the EventEmitter .removeListener. Removes all listeners, or the given listener, for eventname.