Firebase Firestore is a NoSQL document-based database that is part of the Firebase suite of products offered by Google. It allows you to store, retrieve, and manage data in the cloud, and provides real-time synchronization across devices.

In Firestore, documents are organized into collections, and each document is identified by a unique document ID. You can use document references to represent relationships between documents, and retrieve data from referenced documents without making additional requests by using the feature called "subcollections".

Here's an example of how you can get reference data without making additional requests using subcollections in Firestore:

Let's say you have a collection called "users" that contains documents representing user profiles, and each user document has a subcollection called "posts" that contains documents representing posts made by that user.

To retrieve a user's profile data along with their posts, you can use the get() method on the user document reference, and then use the collection() method on the user document reference to access the "posts" subcollection. Here's an example in JavaScript:

javascript
// Assuming you have a Firestore instance initialized and a user document reference const userRef = firebase.firestore().collection('users').doc('user_id'); // Retrieve user profile data userRef.get().then((userSnapshot) => { if (userSnapshot.exists) { const userData = userSnapshot.data(); console.log('User profile data:', userData); // Retrieve user's posts from the "posts" subcollection userRef.collection('posts').get().then((postsSnapshot) => { const postsData = []; postsSnapshot.forEach((postDoc) => { postsData.push(postDoc.data()); }); console.log('User posts:', postsData); }).catch((error) => { console.error('Error getting posts:', error); }); } else { console.error('User not found'); } }).catch((error) => { console.error('Error getting user profile data:', error); });

In this example, you retrieve the user profile data from the user document reference using the get() method, and then retrieve the user's posts data from the "posts" subcollection using the collection() method on the same user document reference. This way, you can retrieve the reference data without making additional requests to Firestore.

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