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LoopBack 4 April 2020 Milestone Update

· 8 min read
Deepak Rajamohan

Originally published on strongloop.com

In April, we focused mostly on completing migration activities, like the migration guide and other related tasks like running existing tests in a LoopBack 3 application after composing it within a LoopBack 4 application. But, that didn't stop us from exploring and adding some cool features.

We now have a new Express package, which enables modeling Express middleware functions as an interceptor chain. Also it is possible now to break a complex application into much smaller components and wire them in a main application. You can find more details on thsese below in Exploring new territories.

Also our community has published many LoopBack 4 extensions in NPM. Many of these extensions are addressing a variety of usecases like pub-sub messaging, mqtt, graphql, rate-limiting, authentication, logging, AWS cloud integration, etc. The extensibility of LoopBack in real time use cases are even surprising us and the possibilities seems to be endless.

Migration Guide​

We have made very good progress with migration guides and LoopBack 3 users should have a solid ground now to explore and migrate to LoopBack 4. The well used LoopBack 3 components are all covered with migrations examples and tutorials. There are certain components which are having fewer downloads per day, that are not covered yet. But we are pursuing steadily to address all migration questions.

Differences in Request-Response Cycle​

We have created a document describing the differences between the request-response cycle in LoopBack 3 and LoopBack 4. Those of you coming from LoopBack 3 will have a better understanding about how the request-response cycle works in LoopBack 4 compared to LoopBack 3.

The LoopBack 4 request-response cycle documentation contains the details in more depth for LoopBack 4.

Example to use Passport Strategies for Authentication in LoopBack 4​

A new Passport Login example is now available. It shows how to use Passport Strategies in LoopBack 4 as an independent authentication step in the application Sequence as well as standard express middleware. If you are using the loopback-component-passport in LoopBack 3, this example can help you migrate your application to LoopBack 4.

Booting Migration Guide​

Because of the architectural differences, the booting process is very different in LoopBack 3 and LoopBack 4. This document describes the differences and lists the various artifacts that take part in the booting process in LoopBack 4.

Custom Validation​

The data coercion and validation and access to data before writing to the databases sections of the LB3 to LB4 request-response migration guide deals with the topic of access and application of custom validation to data in Loopback 4.

Differences between LB3 and LB 4 CLI Commands​

The command line interfaces of LoopBack 3 and LoopBack 4 have some similarities, but also some differences. We have outlined these similarities and differences in Migrating CLI usage patterns.

Exploring New Territories​

The NEW Express Package and Enabling Express Middleware as Interceptors​

The new Express Package, has enabled injecting single and multiple express middleware functions as interceptors into Controller invocations and also as a middleware step in the application Sequence as follows:

The default sequence now has a Middleware step. It creates an invocation chain to call registered middleware handlers with the extension pattern. The sequence can be customized to have more than one Middleware step. Express middleware can also be wrapped as LB4 interceptors, which can in turn be added to global/class/method level. Move built-in cors and openapi endpoints as express middleware functions.

You can check the express middleware page in loopback docs.

Spike - Migrating OAuth2 Component​

In story #3959 we explored the possibility and evaluated the required effort to migrate module loopback-component-oauth2. Considering that LoopBack 4 currently focuses on the integration with third party OAuth 2.0 providers, and the module is complicated, we decide to defer the migration guide and demo a simplified server with OAuth 2.0 enabled on it.

You can find details about the mock server on page migration-auth-oauth2.

Running LoopBack 3 Tests when Mounted on a LoopBack 4 project​

With users being able to mount their LoopBack 3 tests on a LoopBack 4 project, we explored how they can also migrate their LB3 tests onto the LB4 project. Documentation is coming, but if you want to see how an example of how to do it now, see the spike. The spike demonstrates running LB3 tests in the lb3-application example.

Simplify your Complex Applications - Booting Component Applications​

Users can now break down a complex application into much smaller components and wire them all together in a main application, with a new feature to Boot up Component Applications.

APIConnect Extension​

The LoopBack APIConnect extension is now tested by publishing shopping app APIs, enhanced with the extension, on a IBM DataPower Gateway.

We took the shopping example for a close-to-real-life scenario. This would help IBM APIConnect customers to develop their applications with LoopBack and manage them with IBM APIConnect.

Once LoopBack developers have their REST APIs created they could use the LoopBack APIConnect extension to enhance their OpenAPI spec with x-ibm- OpenAPI metadata. For the shopping example, we followed the steps in the example repository to deploy to IBM Cloud and then imported the OpenAPI specification to APIConnect with steps explained in the IBM developer portal.

Miscellaneous​

Extracting JWT Authentication to an Extension Module​

After creating the demo for JWT authentication in loopback4-shopping-example, and applied a similar auth system in access-control-migration, we think it's time to extract the JWT authentication system into a separate extension package, so that people can quickly mount a component to try out the feature.

Last month, we created the extension as authentication-jwt, and its usage is well documented in the README.md file.

Strong-Soap Features and Support​

Strong-Soap now supports validation of anonymous simple types and RPC suffixes.

Customizing Explorer Theme​

As many community users show the interests in changing the look of explorer, we introduced a configuration property called swaggerThemeFile to specify user provided .css themes. For example:

// Inside application constructor
// customize the swagger-ui
this.configure(RestExplorerBindings.COMPONENT).to({
  swaggerThemeFile: '/theme-newspaper.css',
});

You can check the complete guide in section customizing Swagger UI theme.

Move Datasource Configurations from .json to .ts File​

To align with existing typescript files and dynamic configuration of datasources, we have switched datasource configurations to .ts files from LoopBack 3 style json files. Please watch the video tutorial from Miroslav on migrating Migrate LoopBack 4 datasource config to TypeScript.

Build with TS Project-References​

LoopBack monorepo was configured in a hacky way to allow TypeScript to build individual packages. We have made changes to leverage TypeScript's Project-References. Project references are a new feature in TypeScript 3.0 that allow to structure TypeScript projects into smaller pieces.

Other Build Features​

Changes done to make default compilation target as ES2018 and enable all ES2020 features for lib configuration.

Complex OpenAPI Validations​

A list of AJV features have been added in the past few months including AJV keywords, AJV extensibility, AJV service provider and asynchronous validations.

Documentation​

Working with Data​

In LoopBack 4, models describe the shape of data, repositories provide behavior like CRUD operations, and controllers define routes. It's easy to manipulate and query data with LB4. However, for a long time LoopBack 4 documentation was missing the Woring with Data section and users were referencing the old docs in LoopBack 3. Even though LB3 has almost the same querying rules as LB4, the different styles between LB4 and LB3 sometimes are still causing confusion.

Gladly, we added that section with different filters under the page Usage Scenarios - Working with Data. For each filter, we introduced the basic usage with Node.js and REST APIs and also show examples of using both APIs. For instance, we have an example of showing how the limit filter works with Node.js API and also the corresponding example of using REST. 

Node.js API:

await orderRepository.find({limit: 5});

REST:

/orders?filter[limit]=5

Calling APIs with OpenAPI Specification​

If you want to connect to a REST service with an OpenAPI description, the OpenAPI connector would be what you need. We updated the documentation in the Calling other APIs and web services to include this usage. Besides, we added more configuration details in the OpenAPI connector docs page.

Community Contributions​

Added tsdocs for LoopBack Packages​

Autogenerated API docs had descriptions empty for all packages which now fixed by adding ts docs to all packages. Please take a look at the API docs to see the difference.

Consolidate Openapi Schema using a New Spec Enhancer​

LoopBack users will be able to automatically extract schemas used in multiple places into #/components/schemas and replace the references with a $ref, with a new OAS enhancer.

May Milestones​

This month, we would like to work on the remaining items for the migration guide epic, documentation improvement and more. For more detials, take a look at our May milestone list on GitHub.

Call to Action​

In 2020, we look forward to helping you and seeing you around! LoopBack's success depends on you. We appreciate your continuous support and engagement to make LoopBack even better and meaningful for your API creation experience. Here's how you can join us and help the project: