> For the complete documentation index, see [llms.txt](https://guilhermesantos.gitbook.io/niro-health/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://guilhermesantos.gitbook.io/niro-health/modules/imports-by-interface.md).

# Imports by interface

Implementation flexibility and prevent circular dependency.

Imports by interface provide greater implementation flexibility and prevent circular dependency. With interface implementation, it's much easier to test our module, as we can create services that implement this interface.

### Understand how it works.

Using `Nest`, you can implement interfaces instead of the service, and with that, the service starts to implement this interface, for example.

{% code title="cats.interface.ts" %}

```typescript
export interface ICatsService {
  getName(): string;
}
```

{% endcode %}

{% code title="cats.service.ts" %}

```typescript
import { Injectable } from '@nestjs/common';
import type { ICatsService } from './cats.interface';

@Injectable()
export class CatsService implements ICatsService {
  getName() {
    return 'Niro';
  }
}
```

{% endcode %}

To inject our service into another, it would look like this.

{% code title="app.module.ts" %}

```typescript
import { Module } from '@nestjs/common';
import { AppController } from './app.controller';
import { AppService } from './app.service';
import { CatsService } from './cats/cats.service';

@Module({
  controllers: [AppController],
  providers: [
    AppService,
    {
      provide: 'ICatsService',
      useClass: CatsService,
    },
  ],
})
export class AppModule {}
```

{% endcode %}

{% code title="app.service.ts" %}

```typescript
import { Inject, Injectable } from '@nestjs/common';
import type { ICatsService } from './cats/cats.interface';

@Injectable()
export class AppService {
  constructor(
    @Inject('ICatsService')
    private readonly catsService: ICatsService,
  ) {}

  getName() {
    return this.catsService.getName();
  }
}
```

{% endcode %}