Iron-data-table fails to populate data from databinding

Question

The following code taken from this demo works in my app:

https://saulis.github.io/iron-data-table/demo/index.html

<template is="dom-bind">
  <iron-ajax
      url="https://saulis.github.io/iron-data-table/demo/users.json"
      last-response="{{users}}"
      auto>
  </iron-ajax>
  <iron-data-table id="items"
                   selection-enabled 
                   items="[[users.results]]">
    <data-table-column name="Picture" width="50px" flex="0">
      <template>
        <img src="[[item.user.picture.thumbnail]]">
      </template>
    </data-table-column>
    <data-table-column name="First Name">
      <template>[[item.user.name.first]]</template>
    </data-table-column>
    <data-table-column name="Last Name">
      <template>[[item.user.name.last]]</template>
    </data-table-column>
    <data-table-column name="Email">
      <template>[[item.user.email]]</template>
    </data-table-column>
  </iron-data-table>
</template>

But when I change the data source from an iron-ajax call to an internal data binding {{items}}, it does not work.

items-list.html

<template is="dom-bind">
  <iron-data-table id="items"
                   selection-enabled
                   data-source="[[items]]">
    <data-table-column name="Comment" width="50px" flex="0">
      <template>[[item.comment]]</template>
    </data-table-column>
    <data-table-column name="Total">
      <template>[[item.total]]</template>
    </data-table-column>
    <data-table-column name="Merchant">
      <template>[[item.merchant]]</template>
    </data-table-column>
  </iron-data-table>
</template>

I expect the table to populate with data. Instead, the table and column headers render but the data does not populate the table.

A couple of points: I am using Firebase to store the data. And the polymerfire/firebase-query element (in the shown element's parent databound element) to fetch the {{items}} data.

What direction should I head to try to solve this?

Edit

The following describes how and what I am setting to the items variable:

The data structure inside my Firebase is as follows.

https://console.firebase.google.com/project/my-app/database/data

my-app
 |
 - users
    |
    - userid-123
       |
       - nodeid-abc
       |  |- comment: "foo"
       |  |- merchant: "bar"
       |  |- date: "2016-07-02"
       |  |- total: 123
       - nodeid-xyx
          |- comment: "baz"
          |- merchant: "bat"
          |- date: "2016-07-15"
          |- total: 999

I pull that data into my app via Polymerfire firebase-query element in a parent element.

overview-page.html

<firebase-query
    id="query"
    app-name="my-app"
    path="/users/[[user.uid]]"
    data="{{items}}">
</firebase-query>
<items-list id="list"
    items="[[items]]"
    filters="[[filters]]">
</items-list>

I know the {{items}} data is making its way to the list-items element because I set up a button to log the data to the console.

items-list.html

<button on-tap="show">Show</button>
show: function() {
  console.log('items', this.items);
},

When I press the Show button, the console logs the following:

console.log

items
0: Object
   $key: "nodeid-abc"
   comment: "foo"
   merchant: "bar"
   date: "2016-07-02"
   total: 123
1: Object
   $key: "nodeid-xyx"
   comment: "baz"
   merchant: "bat"
   date: "2016-07-15"
   total: 999

Interestingly enough, when I log the same information for the working code example:

show: function(){
  console.log('users', this.users);
}

I get:

console.log

users undefined

Go figure. Obviously, there is something I'm not understanding. Looks like the {{items}} databinding is registering after the iron-data-table renders and, for some reason, the databinding is not updating in the iron-data-table after it registers in the iron-list element.

Edit2

Here is the entire dom-module definition of the items-list element.

<link rel="import" href="../bower_components/polymer/polymer.html">
<link rel="import" href="../bower_components/iron-data-table/iron-data-table.html">
<link rel="import" href="../bower_components/iron-data-table/default-styles.html">

<dom-module id="items-list">
  <template>
    <button on-tap="show">Show</button>
    <template is="dom-bind">
      <iron-data-table items="[[items]]">
        <data-table-column name="Comment">
          <template>[[item.comment]]</template>
        </data-table-column>
        <data-table-column name="Merchant">
          <template>[[item.merchant]]</template>
        </data-table-column>
      </iron-data-table>
    </template>
  </template>
  <script>
    (function() {
      'use strict';
      Polymer({
        is: 'items-list',
        properties: {
          items: {
            type: Array,
            notify: true,
          },
        },
        show: function() {
          console.log('items', this.items);
        },
      });
    })();
  </script>
</dom-module>

Answer 1

You need to remove the extra <template is="dom-bind"> element, it's encapsulating the <iron-data-table> in a separate binding scope. dom-bind isn't needed because you have a binding scope from the dom-module

I assume you copied the dom-bind elements from the demo examples, where they are needed because there isn't a custom element wrapped around the <iron-data-table>. You can see more info on that here: https://www.polymer-project.org/1.0/docs/devguide/templates#dom-bind