Firestore unique index or unique constraint?

Question

Is it possible in Firestore to define an index with a unique constraint? If not, how is it possible to enforce uniqueness on a document field (without using document ID)?

Answer 1

Based on the documentation from this section https://cloud.google.com/firestore/docs/manage-data/add-data#set_a_document

You can simply add a custom identifier when adding document object to a collection as shown below:

const data = {
  name: 'Los Angeles',
  state: 'CA',
  country: 'USA'
};

// Add a new document in collection "cities" with ID 'LA'
const res = await db.collection('cities').doc('LA').set(data);

Using this https://cloud.google.com/firestore/docs/manage-data/add-data#node.js_4 as a reference when you use set as a method on your collection you can be able to specify an id for such document when you need to auto-generate an id you simply use the add method on your collection