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LoopBack 4 July 2019 Milestone Update

· 9 min read
Agnes Lin

Originally published on

This July 20th was the 50th anniversary of The Moon Landing and the famous quote, "That's one small step for man, one giant leap for mankind." This great, memorable event reminds me that every task the LoopBack team finishes will end up enhancing our project. From starting to build new features such as inclusion, to enriching the documentation, we believe that we are making LoopBack better by taking all these small steps!

We finished up 85 story points this month. See the July milestone for an overview of what we have worked on, and read on for more details.

Improvements of Developer Experience

Improvement of @loopback/cli

  • The original CLI version is now stored in the .yo.rc.json file. This allows users to check the version of CLI when upgrading their dependencies. See PR #3338 for details.

  • We refactored the way that the property generator is invoked in the model generator. Now when generating a new model, the loop prompts for adding properties are more robust. See PR #412 for more information.

  • For the CLI lb4 app can now handle a hyphened path and will generate default names properly. See PR #2092 for more details.

New Features in @loopback/context

@config Decorator

In PR #3329, we introduce new config metadata, which allows @config.* to be resolved from a binding other than the current one. For example, before we could inject @config this way:

export class MyRestServer {
// injects `RestServerConfig.port` to the target
host: string,

Now this kind of injection can be done this way:

export class MyRestServer {
// Inject the `` from the application config
@config({fromBinding: 'application', propertyPath: ''})
host: string,

Parameter Injection

The module Context didn't use the invocation context to resolve parameter injection. This might limit some use cases such as @inceptors which couldn't rebind new values. With this implementation, you can use options.skipParameterInjection to resolve parameter injection.

New Options for JSON Schema Generation

We enabled the exclude and optional options to JsonSchemaOptions.


The exclude option takes in an array of model properties which you can exclude from your requestBody. For example, you can exclude the id property from the body of a POST request:

POST /todos

async create(
content: {
'application/json': {
schema: getModelSchemaRef(Note, {exclude: ['id']}),
note: Omit<Note, 'id'>,
): Promise<Note> {
// ...

Any new generated controllers scaffolded by lb4 controller will have the id property excluded by default. See PR #3297 for details.

We also added support for excluding a custom primary key name (not the default id) in PR #3347.


The optional option takes in an array of model properties which you can mark optional in your requestBody. For example, you can mark the foreign key property from the body of a POST request as optional:

POST /todo-lists/{id}/todos

async create(
@param.path.number('id') id: number,
content: {
'application/json': {
schema: getModelSchemaRef(Todo, {
exclude: ['id'],
optional: ['todoListId'],
todo: Omit<Todo, 'id'>,
): Promise<Todo> {
// ...

If this option is set and is not empty, it will override the partial option. See PR #3309 for details.

Simplifying @requestBody

The current @requestBody() only takes in an entire request body (with very nested content object) or infers the schema from the parameter type. To simplify the signature so that users can describe the schema with concise configure options, we explored a new signature in a spike story: @requestBody(spec, model, schemaOptions). Most of the discussions are tracked in PR #3398, and additional opinions and feedback are welcomed before we start implementing the simplified decorator.

Adding Cloud Native Features

To provide observability for LoopBack 4 applications deployed to a cloud environment, we start to add more integrations to expose health, metrics, and distributed tracing data. These packages are positioned as extensions to the framework.

The Health extension has been released as an experimental feature. Two more PRs are up for review:

Documentation Improvements

More Detailed Content for @model and @property Decorators

As we always try to beef up the documentation for LB4, this month we improved docs of the decorators @model and @property. Before we were simply using docs from LB3 site. However, since the implementation structures are different for LB3 and LB4, some parts of the docs are not precise or correct for LB4. We updated the documentation with more details and pointed out the differences between LB3 and LB4. We also added more links so that users can find more references and join the dicussion on GitHub with us. More details are in PR #3354.

Supporting and Documenting Transactions

We also worked on bridging the gap between LoopBack 3 and 4 in terms of exposing transactions from repositories in PR #3397. We've introduced sugar API beginTransaction() at the repository level, which delegates work to the data source that belongs to it to start a transaction.

With it, we've created TransactionalRepository interface that is meant to be used with connectors that support transactions and DefaultTransactionalRepository which can be used for CRUD repositories that support transactions. Once a transaction object is obtained from beginTransaction(), it can be passed into any CRUD calls made for the models attached to the backing datasource. The user can then either call commit() or rollback() actions for the transaction object to persist or revert the changes made.

Note that only select SQL connectors support transactions to use this feature. For more information, check out the documentation.

Connector Reference

Connector reference pages that were missing in the LoopBack 4 docs have been added now. Check issue #2598 for more details.

Code Base Improvements

Running Shared Tests in Connectors

This month we continued refactoring the tests for mysql, mssql, and oracle connectors in LoopBack 3 so that they can run the imported juggler tests in both 3.x and 4.x versions. Now our mongodb, postgresql, kv-redis, cloudant, mysql, mssql, and oracle connectors run shared tests.

Fixing CI Failures

Other Changes

  • We updated our templates and existing examples to leverage getModelSchemaRef in PR #3402.

  • We updated our oracle connector to oracledb v4.0.0 in PR #186.

  • We tested/enabled Node.js 12 for some of our connectors.

  • We fixed an edge case where replaceById was not working for MongoDB database when the data came from the REST API layer. Check issue #3431 and issue #1759 for more details.

  • We removed the source code of @loopback/openapi-v3-types package from our monorepo. This package was deprecated last month in favor of openapi3-ts and @loopback/openapi-v3. Check PR #3385 for more details.

  • We fixed automigrate & autoupdate to wait until the datasource is connected to the database. This addressed a bug in the npm script migrate (scaffolded by lb4 app), where errors thrown by the database migration were not caught correctly and thus the script did not indicate the failure via a non-zero exit code. Check issue #1756 for more details.

  • We improved the type definition of toJSON helper from @loopback/testlab to better support union types like MyModel | null (e.g. as returned by Repository findOne method). Check PR #3823 for more details.

  • We fixed REST API to better handle the case where a custom basePath is configured via app.basePath() API. As a result, the server entry in OpenAPI spec now correctly includes the configured base path again. Check PR #3266 for more details.

  • We fixed a MongoDB connector bug which caused the id from the input data object to be deleted. See issue #3267 for more details.

After many weeks in making, Miroslav finally finished researching how to resolve included models when querying datasources. This concluded the spike issue #2634.

The essence:

  • We will introduce a concept of InclusionResolver functions. These functions implement the logic for fetching related models.
  • Base repository classes (e.g. DefaultCrudRepository) will handle inclusions by calling resolvers registered for individual relations.
  • Model-specific repositories (e.g. TodoRepository scaffolded in your project) will register inclusion resolvers for relations that are allowed to be traversed.
  • LoopBack will provide built-in inclusion resolvers for each relation type we implement (hasMany, belongsTo, hasOne at the time of writing).

The spike PR #3387 shows a proof-of-concept implementation and includes high-level description of the proposed design in the SPIKE document, where you can find more details.

Team Changes

Our LoopBack core maintainer Biniam is leaving to join the API Connect team. His hard work and dedication were an important part of our team. We appreciate the inspiration he gave us and all the contributions he's made. We believe that he will do an outstanding job in the next phase of his career!

Looking for User References

We have updated our website with our users and their testimonials. If you would like to be a part of it, see the details in this GitHub issue.

What's Next?

If you're interested in what we're working on next, you can check out the August milestone.

Call to Action

LoopBack's future 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: