What is Firebase Firestore 'Reference' data type good for?

Question

I'm just exploring the new Firebase Firestore and it contains a data type called reference. It is not clear to me what this does.

• Is it like foreign key?
• Can it be used to point to a collection that is located somewhere else?
• If reference is an actual reference, can I use it for queries? For example can I have a reference that points directly to the user, instead of storing the userId in a text field? And can I use this user reference for querying?

Answer 1

Adding below what worked for me using references in Firestore.

As the other answers say, it's like a foreign key. The reference attribute doesn't return the data of the reference doc though. For example, I have a list of products, with a userRef reference as one of the attributes on the product. Getting the list of products, gives me the reference of the user that created that product. But it doesn't give me the details of the user in that reference. I've used other back end as a services with pointers before that have a "populate: true" flag that gives the user details back instead of just the reference id of the user, which would be great to have here (hopefully a future improvement).

Below is some example code that I used to set the reference as well as get the collection of products list then get the user details from the user reference id given.

Set a reference on a collection:

let data = {
  name: 'productName',
  size: 'medium',
  userRef: db.doc('users/' + firebase.auth().currentUser.uid)
};
db.collection('products').add(data);

Get a collection (products) and all references on each document (user details):

db.collection('products').get()
    .then(res => {
      vm.mainListItems = [];
      res.forEach(doc => {
        let newItem = doc.data();
        newItem.id = doc.id;
        if (newItem.userRef) {
          newItem.userRef.get()
          .then(res => { 
            newItem.userData = res.data() 
            vm.mainListItems.push(newItem);
          })
          .catch(err => console.error(err));
        } else {
          vm.mainListItems.push(newItem);  
        }

      });
    })
    .catch(err => { console.error(err) });

Hope this helps