The requested built-in library is not available on Dartium - mongodb

Question

I am trying to make a very simple application that looks up values in a database by using polymer elements to get input.
My main polymer class looks like this:
library index;
import 'package:polymer/polymer.dart';
import 'lookup.dart';
import 'dart:html';
#CustomTag('auth-input')
class AuthInput extends PolymerElement {
#observable String username = '';
#observable String password = '';
AuthInput.created() : super.created();
void login(Event e, var detail, Node target)
{
int code = (e as KeyboardEvent).keyCode;
switch (code) {
case 13:
{
Database.lookUp(username, password);
break;
}
}
}
}
and a secondary database helper class looks like this:
library database;
import 'package:mongo_dart/mongo_dart.dart';
class Database {
static void lookUp(String username, String password) {
print("Trying to look up username: " + username + " and password: " + password);
DbCollection collection;
Db db = new Db("mongodb://127.0.0.1/main");
db.open();
collection = db.collection("auth_data");
var val = collection.findOne(where.eq("username", username));
print(val);
db.close();
}
}
I keep getting this error and I cannot think of a way around it:
The requested built-in library is not available on Dartium.'package:mongo_dart/mongo_dart.dart': error: line 6 pos 1: library handler failed
import 'dart:io';
The strange thing is, I don't want to use dart:io. The code works fine either running database processes or running polymer processes. I can't get them to work together. I don't see why this implementation of the code will not run.

Answer 1

The first line at https://pub.dartlang.org/packages/mongo_dart says
Server-side driver library for MongoDb implemented in pure Dart.
This means you can't use it in the browser. Your error message indicates the same. The code in the package uses dart:io and therefore can't be used in the browser.
Also mongodb://127.0.0.1/main is not an URL that can be used from within the browser.
You need a server application that does the DB access and provides an HTTP/WebSocket API to your browser client.