Polymer 1.x + Firebase 2.x: How to push or put dat

Question

Using Polymerfire, I want to add new nodes to a Firebase without overwriting data. (I call this push or put behavior.)

In other words. I want to start with this:

State A

my-app
 |
 - emails
    |
    + email1@example,com
    + email2@example,com

And finish with this.

State B

my-app
 |
 - emails
    |
    + email1@example,com
    + email2@example,com
    + email3@example,com
    + email4@example,com

But when I start with State A and do this:

<firebase-document
    id="doc"
    app-name="app"
    data="{{data}}">
</firebase-document>
...
this.$.doc.save('/', 'emails');

I wind up with this:

State B

my-app
 |
 - emails
    |
    + email3@example,com
    + email4@example,com

Notice the starting data: email1@example,com and email2@example,com were deleted.

Here is the Polymerfire documentation. But it doesn't mention anywhere how to accomplish this type of push or put-type method to insert data into a node.

How can I accomplish this?

Edit

The answer by @motss suggests:

this.$.doc('/emails');

instead of

this.$.doc('/', 'emails');

But that does not work because it adds a random auto key as follows:

State B

my-app
 |
 - emails
    |
    - -hvOxpxwjpWHBYGj-Pzqw
       |
       + email3@example,com
       + email4@example,com

Note the added key: -hvOxpxwjpWHBYGj-Pzqw thereby destroys the indexing feature of the data structure.

Answer 1

As far as I know, the save method does things differently in two ways:

1. To set new data into current location.
2. To push new data into current location.

In order to push new data, you have to submit no key as the second argument in the save method:

// This will push new data into the location /emails.
this.$.doc('/emails');

// To set new data (replacing) at location /emails.
this.$.doc('/', 'emails');

Hope this helps IIRC. Correct me if i'm wrong.

Answer 2

I'm going to assume here that the emails are used as keys for objects and are not an array (since you can't have arrays in a Firebase Realtime Database). If that's the case, you probably want something like:

<firebase-query
  id="emails"
  app-name="my-app"
  path="/emails"
  data="{{emails}}">
</firebase-query>
<script>
  // ...
  this.$.emails.ref.child('email3@example,com').set({new: 'data'});
  // ...
</script>

If you don't want to actually query the emails but just want to insert data, that's easy as well using the JS SDK:

firebase.database().ref('emails').child('email3@example,com').set({new: 'data'});

For a third option, you can use <firebase-document> with a path:

<firebase-document
  app-name="my-app"
  path="/emails/[[emailKey]]"
  data="{{emailData}}">
</firebase-document>
<script>
  // ...
  this.emailKey = 'email3@example,com';
  this.emailData = {new: 'data'};
  // ...
</script>