Connect Loopback to a Swagger-compliant API

Usage no npm install needed!

<script type="module">
  import loopbackConnectorSwagger from 'https://cdn.skypack.dev/loopback-connector-swagger';



The Swagger connector enables LoopBack applications to interact with other REST APIs described by the OpenAPI (Swagger) Specification v.2.0.


In your application root directory, enter:

$ npm install loopback-connector-swagger --save

This will install the module from npm and add it as a dependency to the application's package.json file.


To interact with a Swagger API, configure a data source backed by the Swagger connector:

With code:

  var ds = loopback.createDataSource('swagger', {
    connector: 'loopback-connector-swagger',
    spec: 'http://petstore.swagger.io/v2/swagger.json',

With JSON in datasources.json (for example, with basic authentication):

"SwaggerDS": {
    "name": "SwaggerDS",
    "connector": "swagger",
    "spec": "http://petstore.swagger.io/v2/swagger.json",
    "security": {
      "type" : "basic",
      "username": "the user name",
      "password": "thepassword"


As an experimental feature, loopback-connector-swagger is able to cache the result of GET requests.

Important: we support only one cache invalidation mechanism - expiration based on a static TTL value.

To enable caching, you need to specify:

  • cache.model (required) - name of the model providing access to the cache. The model should be extending loopback's built-in KeyValueModel and be attached to one of key-value datasources (e.g. Redis or eXtremeScale).

  • cache.ttl (required) - time to live for cache entries, the value is in milliseconds. Note that certain cache implementations (notably eXtremeScale) do not support sub-second precision for TTL.

Example configuration


  "SwaggerDS": {
    "connector": "swagger",
    "cache": {
      "model": "SwaggerCache",
      "ttl": 100
  "cache": {
    "connector": "kv-redis",


  "name": "SwaggerCache",
  "base": "KeyValueModel",
  // etc.


  "SwaggerCache": {
    "dataSource": "cache",
    "public": false

Data source properties

Specify the options for the data source with the following properties.

Property Description Default
connector Must be 'loopback-connector-swagger' to specify Swagger connector None
spec HTTP URL or path to the Swagger specification file (with file name extension .yaml/.yml or .json). File path must be relative to current working directory (process.cwd()). None
validate When true, validates provided spec against Swagger specification 2.0 before initializing a data source. false
security Security configuration for making authenticated requests to the API. The security.type property specifies authentication type, one of: Basic authentication (basic), API Key (apiKey), or OAuth2 (oauth2). basic


Basic authentication:

security: {
  type: 'basic', // default type, not to be changed
  username: 'the user name',
  password: 'password'

API Key:

security: {
  type: 'apiKey', // default type, not to be changed
  name: 'api_key',
  key: 'yourAPIKey',
  in: 'query' // or 'header'


  type: 'oauth2', // default type, not to be changed
  name: 'oauth_scheme',
  accessToken: 'sampleAccessToken', // access token
  in: 'query' // defaults to `header` if not set

Note: The value of the name property must correspond to a security scheme declared in the Security Definitions object within the spec document.

Creating a model from the Swagger data source

The Swagger connector loads the API specification document asynchronously. As a result, the data source won't be ready to create models until it is connected. For best results, use an event handler for the connected event of data source:

ds.once('connected', function(){
  var PetService = ds.createModel('PetService', {});

Once the model is created, all available Swagger API operations can be accessed as model methods, for example:

PetService.getPetById({petId: 1}, function (err, res){

How model methods are named for given Swagger API Operations:

This connector uses swagger-client which dominates the naming of generated methods for calling client API operations.

Following is how it works:

  • When operationId is present, for example:
paths: {
    operationId: weather.forecast

Here, as operationId is present in Swagger specification, the generated method is named equivalent to operationId.

Note: if operationId is of format equivalent to calling a nested function such as: weather.forecast, the resulting method name will replace . with _ i.e. weather.forecast will result into weather_forecast.This means you can call MyModel.weather_forecast() to access this endpoint programmatically.

  • When operationId is not provided in Swagger specification, the method name is formatted as following: <operationType (i.e. get, post, etc)> + _ + <path parts separated by underscores>

For example:


for above operation, the resulting method name will be: get_weather_forecast.

This means you can call MyModel.get_weather_forecast() to access this endpoint programmatically.

Extend a model to wrap/mediate API Operations

Once you define the model, you can wrap or mediate it to define new methods. The following example simplifies the getPetById operation to a method that takes petID and returns a Pet instance.

  PetService.searchPet = function(petID, cb){
    PetService.getPetById({petId: petID}, function(err, res){
      if(err) cb(err, null);
      var result = res.data;
      cb(null, result);

This custom method on the PetService model can be exposed as REST API end-point. It uses loopback.remoteMethod to define the mappings:

  PetService.searchPet, {
    accepts: [
      { arg: 'petID', type: 'string', required: true,
        http: { source: 'query' }
    returns: {arg: 'result', type: 'object', root: true },
    http: {verb: 'get', path: '/searchPet'}


Coming soon...