Use Elasticsearch Update API

[llvtt]

This can replace the retrieve + apply strategy that we currently use in the Elastic DocManager. See the following:

• http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/docs-update.html
• http://elasticsearch-py.readthedocs.org/en/master/api.html#elasticsearch.Elasticsearch.update

We'll need something that can transform MongoDB "update specs" (e.g. {$set: {"x.y.z": 42}}) to Elasticsearch update scripts. I don't believe we can use partial documents (as opposed to scripts) to update docs stored in Elasticsearch, because there doesn't seem to be a way to nullify a field that way.

[xmasotto]

As Luke noted, there are two ways to apply updates using elastic search. One is to pass a partial document which will be merged with the document, which can add/update fields but not remove them. The second and more flexible option is to send a javascript snippet that will be execute and to produce the updated document. Unfortunately, dynamic scripting (sending the script as a string to the server) has some restrictions, and appears to be disabled by default. (http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/modules-scripting.html) I'm not sure what they mean by "sandboxed language", so I'll have to look into that more.

In order to support the full update functionality, we probably would need users to enable dynamic scripting in configuration, which might be undesirable for default behavior.

[vvaradhan]

@xmasotto From http://www.elasticsearch.org/blog/elasticsearch-1-3-0-released/ - groovy and Lucene expression are default sandboxed languages. Sandbox restricts the use of certain classes/methods - for example: java.lang.System and .getClass() in every object would be blocked and can't be used.

[vvaradhan]

@xmasotto As for default configuration, as of 1.3.0, it is defaulted to "sandbox".