One of the framework features that attracts application developers is productivity. In Loopback 4 the command line interface plays an important role to achieve it. If you are building a Loopback 4 application that interacts with a database and exposes CRUD operations, your flow might be as follows:

  • Create an Application
  • Add a Datasource
  • Add a Model
  • Add a Repository
    • Needs a Datasource and a Model
  • And finally add a Controller
    • Needs a Model and a Repository

Usually, after defining your datasource(s) you start defining your model(s) based on your design and then create the repositories that will serve as the glue between datasources and models to finally create the controllers that will be interacting with client applications, executing business logic and invoking repository methods.

To support this flow completely and start achieving productivity, we welcome the recently addition to the CLI options, lb4 repository. This option is very powerful and can accept multiple models, infer their ID property and generate a repository for each of them in one single command.

The team is working very hard in the underlying code to support these options and make the framework more stable on each release, knowing in advance that reliability is also a priority for any real world project.

NOTE: We usually create the models first and then we move toward the rest of the components such as repositories, thus, having the option to accept multiple models can really save us a lot of time.

Command Line Arguments

For now, let’s assume we already have a Datasource named ds which is coming from the property name located in the src/datasources/ds.datasource.json and a Model named MyModel declared in the src/repositories/my-model.repository.ts file.

We can create a repository with the following command line:

lb4 repository --datasource ds --model myModel

Note: The final repository name match automatically the associated model, however you can also specify a custom name with lb4 repository myRepoName.

The file my-model.repository.ts will be created in src/repositories and its content is listed below.

import { DefaultCrudRepository, juggler } from "@loopback/repository";
import { MyModel } from "../models";
import { DsDataSource } from "../datasources";
import { inject } from "@loopback/core";

export class MyModelRepository extends DefaultCrudRepository<
> {
  constructor(@inject("datasources.ds") dataSource: DsDataSource) {
    super(MyModel, dataSource);

NOTE: As you can see in the listing above, lb4 repository extends automatically either DefaultCrudRepository or DefaultKeyValueRepository depending upon the datasource selected.

You will notice that one of the lb4 repository features is the ability to infer the ID property from the model file in src/models. In the listing above, you see that this property name is id but can be any name, it is really up to your database design.

In case lb4 repository could not infer the ID property name, it will prompt you for it.

? **Please enter the name of the ID property for MyModel:** (id)

By default it suggests the id property name but you can type any name that reflects your design strategy.

You also have the option to specify the IDproperty name from the command line with the --id as follows.

lb4 repository myrepo --datasource ds --model myModel --id mykey

Interactive Prompts

If you specify an invalid Datasource or Model or simply you don’t specify any from the command line, CLI will prompt and guide you through interactive prompts. Let’s run the following command:

lb4 repository

CLI will read the src/models and src/datasources directories, and then will present you the option to select the Datasource and then the model(s) that you want a repository to be generated for.

Select a DataSource

? **Please select the datasource** (Use arrow keys)
> DsDatasource

Note: As you can see, in the interactive prompt above, the full data source class name is showed in the list.

Select Model(s)

Next it will prompt you for the model(s). Here you are able to select more than one model using the space bar and the arrow keys to move up and down.

? **Select the model(s) you want to generate a repository**
◯ Product
◯ Item
❯◯ MyModel
❯◯ Customer

Notice that models MyModel and Customer were selected above. CLI will create two repositories with a set of final messages as follows:

create src/repositories/customer.repository.ts
create src/repositories/my-model.repository.ts
update src/repositories/index.ts
update src/repositories/index.ts

Repositories Customer,MyModel were created in src/repositories/

I hope you find in lb4 repository and the rest of the CLI options a useful tool to achieve productivity in your next project.

Call for Action

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