Data model
Firestore is a NoSQL, document-oriented database. Unlike a SQL database, there are no tables or rows. Instead, you store data in documents, which are organized into collections.
Each document contains a set of key-value pairs. Firestore is optimized for storing large collections of small documents.
All documents must be stored in collections. Documents can contain subcollections and nested objects, both of which can include primitive fields like strings or complex objects like lists.
Collections and documents are created implicitly in Firestore. Simply assign data to a document within a collection. If either the collection or document does not exist, Firestore creates it.
Documents
In Firestore, the unit of storage is the document. A document is a lightweight record that contains fields, which map to values. Each document is identified by a name.
A document representing a user alovelace
might look like this:
alovelace
first : "Ada"
last : "Lovelace"
born : 1815
Complex, nested objects in a document are called maps. For example, you could structure the user's name from the example above with a map, like this:
alovelace
name :
first : "Ada"
last : "Lovelace"
born : 1815
You may notice that documents look a lot like JSON. In fact, they basically are. There are some differences (for example, documents support extra data types and are limited in size to 1 MB), but in general, you can treat documents as lightweight JSON records.
Collections
Documents live in collections, which are simply containers for documents. For
example, you could have a users
collection to contain your various users, each
represented by a document:
users
alovelace
first : "Ada"
last : "Lovelace"
born : 1815
aturing
first : "Alan"
last : "Turing"
born : 1912
Firestore is schemaless, so you have complete freedom over what fields you put in each document and what data types you store in those fields. Documents within the same collection can all contain different fields or store different types of data in those fields. However, it's a good idea to use the same fields and data types across multiple documents, so that you can query the documents more easily.
A collection contains documents and nothing else. It can't directly contain raw fields with values, and it can't contain other collections. (See Hierarchical Data for an explanation of how to structure more complex data in Firestore.)
The names of documents within a collection are unique. You can provide your own keys, such as user IDs, or you can let Firestore create random IDs for you automatically.
You do not need to "create" or "delete" collections. After you create the first document in a collection, the collection exists. If you delete all of the documents in a collection, it no longer exists.
References
Every document in Firestore is uniquely identified by its location
within the database. The previous example showed a document alovelace
within
the collection users
. To refer to this location in your code, you can create a
reference to it.
Web version 9
import { doc } from "firebase/firestore"; const alovelaceDocumentRef = doc(db, 'users', 'alovelace');
Web version 8
var alovelaceDocumentRef = db.collection('users').doc('alovelace');
Swift
let alovelaceDocumentRef = db.collection("users").document("alovelace")
Objective-C
FIRDocumentReference *alovelaceDocumentRef = [[self.db collectionWithPath:@"users"] documentWithPath:@"alovelace"];
Kotlin
Android
val alovelaceDocumentRef = db.collection("users").document("alovelace")
Java
Android
DocumentReference alovelaceDocumentRef = db.collection("users").document("alovelace");
Dart
final alovelaceDocumentRef = db.collection("users").doc("alovelace");
Java
Python
Python
(Async)
C++
DocumentReference alovelace_document_reference = db->Collection("users").Document("alovelace");
Node.js
Go
PHP
PHP
To authenticate to Firestore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.
Unity
DocumentReference documentRef = db.Collection("users").Document("alovelace");
C#
C#
To authenticate to Firestore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.
Ruby
A reference is a lightweight object that just points to a location in your database. You can create a reference whether or not data exists there, and creating a reference does not perform any network operations.
You can also create references to collections:
Web version 9
import { collection } from "firebase/firestore"; const usersCollectionRef = collection(db, 'users');
Web version 8
var usersCollectionRef = db.collection('users');
Swift
let usersCollectionRef = db.collection("users")
Objective-C
FIRCollectionReference *usersCollectionRef = [self.db collectionWithPath:@"users"];
Kotlin
Android
val usersCollectionRef = db.collection("users")
Java
Android
CollectionReference usersCollectionRef = db.collection("users");
Dart
final usersCollectionRef = db.collection("users");
Java
Python
Python
(Async)
C++
CollectionReference users_collection_reference = db->Collection("users");
Node.js
Go
PHP
PHP
To authenticate to Firestore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.
Unity
CollectionReference collectionRef = db.Collection("users");
C#
C#
To authenticate to Firestore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.
Ruby
For convenience, you can also create references by specifying the path to a
document or collection as a string, with path components separated by a forward
slash (/
). For example, to create a reference to the alovelace
document:
Web version 9
import { doc } from "firebase/firestore"; const alovelaceDocumentRef = doc(db, 'users/alovelace');
Web version 8
var alovelaceDocumentRef = db.doc('users/alovelace');
Swift
let aLovelaceDocumentReference = db.document("users/alovelace")
Objective-C
FIRDocumentReference *aLovelaceDocumentReference = [self.db documentWithPath:@"users/alovelace"];
Kotlin
Android
val alovelaceDocumentRef = db.document("users/alovelace")
Java
Android
DocumentReference alovelaceDocumentRef = db.document("users/alovelace");
Dart
final aLovelaceDocRef = db.doc("users/alovelace");
Java
Python
Python
(Async)
C++
DocumentReference alovelace_document = db->Document("users/alovelace");
Node.js
Go
PHP
PHP
To authenticate to Firestore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.
Unity
DocumentReference documentRef = db.Document("users/alovelace");
C#
C#
To authenticate to Firestore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.
Ruby
Hierarchical Data
To understand how hierarchical data structures work in Firestore, consider an example chat app with messages and chat rooms.
You can create a collection called rooms
to store different chat rooms:
rooms
roomA
name : "my chat room"
roomB
...
Now that you have chat rooms, decide how to store your messages. You might not want to store them in the chat room's document. Documents in Firestore should be lightweight, and a chat room could contain a large number of messages. However, you can create additional collections within your chat room's document, as subcollections.
Subcollections
The best way to store messages in this scenario is by using subcollections. A subcollection is a collection associated with a specific document.
You can create a subcollection called messages
for every room document in
your rooms
collection:
rooms
roomA
name : "my chat room"
messages
message1
from : "alex"
msg : "Hello World!"
message2
...
roomB
...
In this example, you would create a reference to a message in the subcollection with the following code:
Web version 9
import { doc } from "firebase/firestore"; const messageRef = doc(db, "rooms", "roomA", "messages", "message1");
Web version 8
var messageRef = db.collection('rooms').doc('roomA') .collection('messages').doc('message1');
Swift
let messageRef = db .collection("rooms").document("roomA") .collection("messages").document("message1")
Objective-C
FIRDocumentReference *messageRef = [[[[self.db collectionWithPath:@"rooms"] documentWithPath:@"roomA"] collectionWithPath:@"messages"] documentWithPath:@"message1"];
Kotlin
Android
val messageRef = db .collection("rooms").document("roomA") .collection("messages").document("message1")
Java
Android
DocumentReference messageRef = db .collection("rooms").document("roomA") .collection("messages").document("message1");
Dart
final messageRef = db .collection("rooms") .doc("roomA") .collection("messages") .doc("message1");
Java
Python
Python
(Async)
C++
DocumentReference message_reference = db->Collection("rooms") .Document("roomA") .Collection("messages") .Document("message1");
Node.js
Go
PHP
PHP
To authenticate to Firestore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.
Unity
DocumentReference documentRef = db .Collection("Rooms").Document("RoomA") .Collection("Messages").Document("Message1");
C#
C#
To authenticate to Firestore, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.
Ruby
Notice the alternating pattern of collections and documents. Your collections and documents must always follow this pattern. You cannot reference a collection in a collection or a document in a document.
Subcollections allow you to structure data hierarchically, making data easier to
access. To get all messages in roomA
, you can create a collection reference
to the subcollection messages
and interact with it like you would any other
collection reference.
Documents in subcollections can contain subcollections as well, allowing you to further nest data. You can nest data up to 100 levels deep.