Add flag to exclude instance properties from enumeration

[flacnut]

We would like to be able to have certain properties not get serialized by JSON.stringify. Eg:

orm.define('user', {
    login: {
      type: 'text',
      required: true,
    },
    password: {
      type: 'text',
      required: true,
      enumerable: false   // <--- Supported with this PR
    },
   // ... other properties
});

expressApp.get('/user', (req, res) => {
  orm.user.get(req.userId, (err, user) => {
    if (err) { /*500*/ }
    res.send(user); // will call JSON.stringify - we don't want to send the password!
  });
});

Currently we have a serialize() method declared on the user definition which only includes properties we want. We call res.send(user.serialize()) but this isn't recursive, is quite unclean, and can potentially allow us to 'leak' secret properties if we are forgetful to call .serialize().

When this merges I will update the Wiki accordingly.

[dxg]

I really like this idea, but it would be better to handle this at the source as we do with required so that every property has enumerable set.

Also, this PR needs some tests.

[flacnut]

Nice, I'll move this code this week. I'll also add some tests (I tried to run them on my macbook but had some issues. I'll investigate further...)

[flacnut]

prop may be undefined when key is value on a 'hasMany' relationship.

[flacnut]

@dxg Updated - I was trying to find where the required: true tests are to put the enumerable: true tests beside it. This was the next best location I could find.

[dxg]

👍