---
title: subcollection
description: Pipeline source helper that targets a subcollection relative to the current document context.
next: /firestore/pipelines/sdk-compatibility
previous: /firestore/pipelines/timestamp-extract
---

`subcollection()` creates a **detached pipeline** aimed at a subcollection path relative to each parent document in the outer pipeline. The returned pipeline has no database instance and cannot be executed directly. Embed it in another pipeline with `toScalarExpression()` or `toArrayExpression()`.

Import from the pipelines entry point:

```js
import {
  subcollection,
  field,
  countAll,
  average,
} from '@react-native-firebase/firestore/pipelines';
```

# Basic example

```js
import { getFirestore } from '@react-native-firebase/firestore';
import {
  execute,
  field,
  subcollection,
  countAll,
  average,
} from '@react-native-firebase/firestore/pipelines';

const db = getFirestore('your-enterprise-database-id');

const snapshot = await execute(
  db
    .pipeline()
    .collection('restaurants')
    .addFields(
      subcollection('reviews')
        .aggregate(countAll().as('reviewCount'), average('rating').as('avgRating'))
        .toScalarExpression()
        .as('reviewSummary'),
    )
    .select('name', field('reviewSummary')),
);

snapshot.results.forEach(row => {
  const summary = row.data().reviewSummary;
  console.log(row.data().name, summary.reviewCount, summary.avgRating);
});
```

# Options object

Pass a `SubcollectionStageOptions` object when you need raw stage options:

```js
subcollection({ path: 'reviews', rawOptions: {} });
```

# Related helpers

| Helper                      | Use when                                           |
| --------------------------- | -------------------------------------------------- |
| `subcollection`             | Target a subcollection relative to each parent doc |
| `toScalarExpression()`      | Embed a nested pipeline as a single scalar field   |
| `toArrayExpression()`       | Embed a nested pipeline as an array of documents   |
| `SubcollectionStageOptions` | Options type for the subcollection source stage    |

# Upstream reference

See the [firebase-js-sdk `subcollection` declaration](https://firebase.google.com/docs/reference/js/firestore_pipelines#subcollection) for overload signatures and nested pipeline usage.