datatstore: Provide a way to get the generated ID from a Key object

[rakyll]

var key = ds.key('Kind', null)
ds.put({
  key: key,
  data: //...
}, function(err, key) {
   /// how to i read the key ID?
});

[stephenplusplus]

Any thoughts for how to provide this? An id property on the Key object? Exposing a getId method to return the last item in the path array (would that even work?)?

This also got me thinking. Well, 1: we don't have a put method, but I assume you meant save :) And 2: if it's not too much magic, we could update the key object reference passed in to save, as opposed to only returning a new key object in the callback. The callback would behave as it currently does, but would also update the original key object.

If you have an idea for an implementation, I'm happy to give it a shot.

[rakyll]

Exposing a getId method to return the last item in the path array (would that even work?)?

This would work.

But we should additionally provide a pseudo getter for the full path as well. Parent entity keys should be recoverable as well.

The callback would behave as it currently does, but would also update the original key object.

This doesn't fix the problem of not being able to read the ID. You would like to use the ID somewhere else (e.g. as a key to memcache or on the URL to the item's detail page).

We should at least have a getId and getPath before the release.

[rakyll]

Look what @proppy has done https://github.com/proppy/gcloud-node-todos/blob/master/server.js#L31 :)

[stephenplusplus]

This doesn't fix the problem of not being able to read the ID.

Nope, was just to be a convenience, since currently you would be left with 2 keys that were meant to refer to the same thing. I'll give it a shot, then run it by you via PR.

[stephenplusplus]

#175 should fix this issue. I'll work on the second part soon.

[stephenplusplus]

It sounds like we decided against providing this feature. The link to @proppy's code shows how you can get the id:

key.path_.pop(); // possibly `key.path.pop()` soon.

Re-open if I was mistaken, and this feature can be achieved reliably.