LokiJS: insert existing value for index doesn't error - how to make unique indices?

Question

if I try to override an existing indexed field, I do not get an error. It should error, because it is not update()!

var loki = require('lokijs');
var db = new loki('test.json');
var users = db.addCollection('users', { indices: ['userID']});
users.insert(
   {
     'name': 'Anna',
     'userID': 1
   },
   {
     'name': 'Bernd',
     'userID': 2
   },
   {
     'name': 'Christa',
     'userID': 3
   });
db.save();
users.insert({'name': 'Dieter','userID': 2}); // this should error!!

How can I make an unique index to get an error when trying to inset an existing userID ?

Answer 1

var loki = require('lokijs');
var db = new loki('test.json');
var users = db.addCollection('users', { indices: ['userID']});
users.ensureUniqueIndex('userID');

users.on('error',function(obj){
  console.log('error ... adding 1 to userID');
  obj.userID = obj.userID+1;
  return obj;
});
users.insert(
   {
     'name': 'Anna',
     'userID': 1
   });
users.insert(
    {
     'name': 'Bernd',
     'userID': 2
   });
users.insert(   
  {
     'name': 'Christa',
     'userID': 3
   });
db.save();
console.log(users.data);
try {
users.insert({'name': 'Dieter','userID': 2}); // this should error!!

} catch(e){
  var i = 2+1;
  users.insert({'name': 'Dieter','userID': i}); // this should error!!

}
db.save();
db2 = new loki('test.json');
db2.loadDatabase({}, function () {
  var users2 = db2.getCollection('users')
  console.log(users2.data);
});

Either users.on('error',...) nor try{ users.insert...} catch(e){// id+1} handles the thrown error

That's my console:

[ { name: 'Anna',
    userID: 1,
    meta: { revision: 0, created: 1436186694342, version: 0 },
    '$loki': 1 },
  { name: 'Bernd',
    userID: 2,
    meta: { revision: 0, created: 1436186694342, version: 0 },
    '$loki': 2 },
  { name: 'Christa',
    userID: 3,
    meta: { revision: 0, created: 1436186694342, version: 0 },
    '$loki': 3 } ]
Duplicate key for property userID: 2
[ { name: 'Anna',
    userID: 1,
    meta: { revision: 0, created: 1436186694342, version: 0 },
    '$loki': 1 },
  { name: 'Bernd',
    userID: 2,
    meta: { revision: 0, created: 1436186694342, version: 0 },
    '$loki': 2 },
  { name: 'Christa',
    userID: 3,
    meta: { revision: 0, created: 1436186694342, version: 0 },
    '$loki': 3 },
  { name: 'Dieter',
    userID: 2,
    meta: { revision: 0, created: 0, version: 0 },
    '$loki': 4 } ]