@loopback/docs/site/Relation-generator.md

Documentation for LoopBack 4

---
lang: en
title: 'Relation generator'
keywords: LoopBack 4.0, LoopBack 4
sidebar: lb4_sidebar
permalink: /doc/en/lb4/Relation-generator.html
---

### Prerequisites

Important: Before running this generator, make sure the models, datasource, and
repositories involved in this relation exist. Then, inside your LoopBack
application, run the command from the root directory.

{% include content/generator-create-app.html lang=page.lang %}

### Synopsis

Adds a new `Relation` between existing source and target models in a LoopBack
application.

```sh
lb4 relation [options]
```

### Options

- `-h`, `--help`: Print the generator’s options and usage.
- `--skip-cache`: Do not remember prompt answers. Default: `false`.
- `--skip-install`: Do not automatically install dependencies. Default: `false`.
- `--force-install`: Fail on install dependencies error. Default: `false`.
- `--relationType`: Relation type.
- `--sourceModel`: Source model.
- `--destinationModel`: Destination model.
- `--foreignKeyName`: Destination model foreign key name.
- `--relationName`: Relation name.
- `-c`, `--config`: JSON file name or value to configure options.
- `-y`, `--yes`: Skip all confirmation prompts with default or provided value.
- `--format`: Format generated code using `npm run lint:fix`.

### Arguments

Defining lb4 relation in one command line interface (cli):

```sh
lb4 relation --sourceModel=<sourceModel>
--destinationModel=<destinationModel> --foreignKeyName=<foreignKeyName>
--relationType=<hasMany|belongsTo> [--relationName=<relationName>] [--format]
```

- `<relationType>` - Type of the relation that will be created between the
  source and target models.

- `<sourceModel>` - Name of the model to create the relationship from.

- `<destinationModel>` - Name of the model to create a relationship with.

- `<foreignKeyName>` - Property that references the primary key property of the
  destination model.

- `<relationName>` - Name of the relation that will be created.

### Interactive Prompts

The tool will prompt you for:

- **Relation `type` between models.** _(relationBaseClass)_ Prompts a list of
  available relations to choose from as the type of the relation between the
  source model and the target model. Supported relation types:

  - [HasMany](HasMany-relation.md)
  - [BelongsTo](BelongsTo-relation.md)

- **Name of the `source` model.** _(sourceModel)_ Prompts a list of available
  models to choose from as the source model of the relation.

- **Name of the `target` model.** _(targetModel)_ Prompts a list of available
  models to choose from as the target model of the relation.

- **Name of the `Source property`.** _(relationName)_ Prompts for the Source
  property name. Note: Leave blank to use the default.

  Default values:

  - `<targetModel><targetModelPrimaryKey>` for `belongsTo` relations, e.g.
    `categoryId`
  - plural form of `<targetModel>` for `hasMany` relations, e.g. `products`

- **Name of Foreign key** _(foreignKeyName)_ to be created in target model. For
  hasMany relation type only, default: `<sourceModel><sourceModelPrimaryKey>`.
  Note: Leave blank to use the default.

### Output

Once all the prompts have been answered, the CLI will update or create source
files for the Entities involved in the relation.

- Update source Model class as follows:
  `/src/models/${sourceModel-Name}.model.ts`
- Update target Model class as follows:
  `/src/models/${targetModel-Name}.model.ts`
- Update source Model Repository class as follows:
  `/src/repositories/${sourceModel-Repository-Name}.repository.ts`
- Update target Model Repository class as follows:
  `/src/repositories/${targetModel-Repository-Name}.repository.ts`
- Create a Controller for the new relation as follows:
  `/src/controllers/{sourceModel-Name}-{targetModel-Name}.controller.ts`
- Update `/src/controllers/index.ts` to export the newly created Controller
  class.