How to Generate Auto ID in Firestore: Simple Guide

In Firestore, you can generate an automatic unique ID by using the add() method on a collection, which creates a new document with a generated ID. Alternatively, use doc() without arguments to get a reference with an auto-generated ID before setting data.

Syntax

Firestore provides two main ways to generate an automatic ID for a new document:

• collectionRef.add(data): Adds a new document with an auto-generated ID and sets the data.
• collectionRef.doc(): Creates a document reference with a new auto-generated ID without data. You can then use set() to add data.

Both methods ensure unique IDs without manual input.

javascript

const docRef = collectionRef.doc();
const autoId = docRef.id;
await docRef.set(data);

// Or simpler:
await collectionRef.add(data);

Example

This example shows how to add a new user document with an auto-generated ID using add(). It also shows how to get the ID when using doc() and set().

javascript

import { getFirestore, collection, addDoc, doc, setDoc } from 'firebase/firestore';

const db = getFirestore();
const usersRef = collection(db, 'users');

// Using add() to generate ID and add data
async function addUser() {
  const userData = { name: 'Alice', age: 30 };
  const docRef = await addDoc(usersRef, userData);
  console.log('User added with ID:', docRef.id);
}

// Using doc() to get auto ID, then set data
async function addUserWithDoc() {
  const newDocRef = doc(usersRef); // auto ID generated
  const userData = { name: 'Bob', age: 25 };
  await setDoc(newDocRef, userData);
  console.log('User added with ID:', newDocRef.id);
}

addUser();
addUserWithDoc();

Output

User added with ID: XyZ123abc
User added with ID: AbC456def

Common Pitfalls

Common mistakes when generating auto IDs in Firestore include:

• Trying to set a document with an empty string or manual ID instead of letting Firestore generate it.
• Using doc(id) with a fixed string which can cause ID collisions.
• Not awaiting asynchronous calls like addDoc() or setDoc(), leading to unexpected behavior.

Always use add() or doc() without parameters for unique IDs and await the promises.

javascript

/* Wrong way: manually setting empty string ID */
const wrongDocRef = collectionRef.doc(''); // Not recommended
await wrongDocRef.set(data);

/* Right way: auto ID generation */
const rightDocRef = collectionRef.doc();
await rightDocRef.set(data);

Quick Reference

Summary tips for generating auto IDs in Firestore:

• Use collectionRef.add(data) for quick add with auto ID.
• Use collectionRef.doc() to get a new ID reference before setting data.
• Always await asynchronous Firestore calls.
• Avoid manual or empty string IDs to prevent collisions.

Key Takeaways

Use collectionRef.add(data) to create a document with an auto-generated ID easily.

Use collectionRef.doc() without arguments to get a new document reference with an auto ID before setting data.

Always await Firestore async calls like addDoc() and setDoc() to ensure proper execution.

Avoid manually setting document IDs as empty strings or fixed values to prevent conflicts.

Auto-generated IDs are unique and safe for concurrent writes.