Add support for key_as_string for term aggregation

[ppf2]

The REST API term aggregation returns key_as_string as a "friendly" timestamp in addition to key (epoch time) in the response. But key_as_string is getting skipped in NEST. Would be nice to add key_as_string to KeyItem so that it can be retrieved as a field from KeyItem along with Key and DocCount.

"aggregations": {
      "test": {
         "buckets": [
            {
               "key": 1373814509000,
               "key_as_string": "2013-07-14T15:08:29.000Z",
               "doc_count": 1
            },
            {
               "key": 1371222509000,
               "key_as_string": "2013-06-14T15:08:29.000Z",
               "doc_count": 1
            }
         ]
      }
   } 

[ppf2]

Actually, will help further if we provide a way to return the key value as a .net DateTime object.

[gmarz]

@ppf2, the reason for skipping key_as_string is to keep backwards compatibility with earlier versions of ES where that property doesn't exist. See #730 for some background.

I agree we should support key_as_string and handle this better. I'm also +1 for providing a way to retrieve the key as a DateTime object (if it is one).

Thanks for reporting this!

[gmarz]

@ppf2 I just pushed 8505c4f which adds support for key_as_string.

[ppf2]

@gmarz thx!

[gmarz]

@ppf2 no problem.

Also, on second thought, in regards to providing a way to retrieve a key as DateTime, I think it might be best to leave that up to the user. The problem is that a key could be other values other than a date (numeric, text) and NEST shouldn't make any assumptions.

What do you think?

[gmarz]

@ppf2 closing this unless you have any objections to the above. Feel free to re-open if so.