Support Multi Search API

[mpenet]

see http://www.elasticsearch.org/guide/reference/api/multi-search.html

I don't think you support it yet (I didn't see it in the docs).
It uses the same format as bulk, so maybe it's something to think about when implementing #11

[michaelklishin]

I did not implement it in 1.0 because it seemed like a non-essential feature we also did not have good API ideas for. Now it's time. Hopefully in 1.1. I agree that it can learn a lot from what is done for #11.

[michaelklishin]

Also, feel free to take a crack at it, following #11 implementation as a guideline.

[mpenet]

I think I will wait for you to release the native client support, this could prevent doing the work twice (I could be wrong, I am not really familiar with Elastisch codebase). But yeah I agree it's really not something essential, just something missing (I have no use for it personally).

[boutros]

I have a need for multi search. Is anyone working on this?

[michaelklishin]

Not that I'm aware of.

[boutros]

Ok, I'll have a go at it

[boutros]

I finally got around to looking into this today. I made a first draft modelled after the bulk API:
https://github.com/boutros/elastisch/commits/multi-search

Example usage:

(require '[clojurewerkz.elastisch.rest.multi :as multi]
         '[clojurewerkz.elastisch.query :as query]
         '[clojurewerkz.elastisch.rest :as esr])

(def queries-with-headers
  [{:index "people"} {:query (query/match-all) :size 1}
   {:index "articles"} {:query (query/match-all) :size 1}])

(esr/connect "http://localhost:9200")

(multi/search queries-with-headers)
=> {:responses [...]}

The headers must be interleaved with the queries. Maybe we should make helper functions for when headers are empty/not needed? eg. when using the multi/search-with-index version, when all queries targets the same index.

I haven't worked with the native client yet, but I assume it easily can be done. Should add some tests and docs too. Anyway, the supplied solution fulfills my needs, but please let me know what else is missing.

I'm neither a Clojure nor Elasticsearch expert, so I'd appreciate if someone could see if this make sense.

[michaelklishin]

Looks like a good starting point. I have a question: what keys will be present in the returned map? Can we simply return a list/sequence or the map is necessary for some reason?

Thank you!

[boutros]

:responses is the only key in the result map, so you are right it would be better to just return the seq of the query responses. The only exception would be if the requests fails completely, in which case an object with an error message will be returned instead, according to the ES docs: http://www.elasticsearch.org/guide/reference/api/multi-search/

I have never experienced such failure. I couldnt really find how failures in general are handled in Elastisch - is it mainly left to the user to deal with?

The order of the responses matches the order of queries, so that's how you identify which is which.

[michaelklishin]

Non-2xx or 3xx responses will result in an exception.

[boutros]

Right, so then the search functions only have to consider the "happy path", and can safely discard the map and simply return a vector of the responses.

I'll write some test cases and docs tomorrow

[michaelklishin]

Thank you!

[michaelklishin]

Fixed for HTTP client with #33.