Backwards compat for users running map reduce jobs that use riak_kv_counter

[russelldb]

Also add similar convenience functions for 2.0+ data types to riak_kv_crdt.

[seancribbs]

typo "Backwards"

[seancribbs]

Will this raise an error if the type is a 2.0 counter instead of a 1.4 counter? What happens after the upgrade completes?

[russelldb]

no, you'll get a zero, like if you asked for a counter and it was a set, map, or regular riak_object

[seancribbs]

So these are helpful, but I'd really love to see riak_kv_mapreduce wrappers around these so you can actually use them without writing your own functions. That said, it's a "nice-to-have" and can wait.

I made this module to test with:

-module(crdtmr).
-export([map_value/3]).
-include_lib("riak_kv/include/riak_kv_types.hrl").

map_value(RObj, <<"legacy_counter">>, _) ->
    [ riak_kv_counter:value(RObj) ];
map_value(RObj, _, <<"legacy_counter">>) ->
    [ riak_kv_counter:value(RObj) ];
map_value(RObj, _, _) ->
    {Type, Value} = riak_kv_crdt:value(RObj),
    [ riak_kv_crdt_json:fetch_response_to_json(Type, Value, undefined, ?MOD_MAP) ].

Here's the JSON of a sample job I sent from the Ruby client:

{"inputs":["maps","test"],"query":[{"map":{"language":"erlang","keep":true,"module":"crdtmr","function":"map_value"}}]}

...and here was the output:

[{"type"=>"map", "value"=>{"likes_counter"=>10, "friends_set"=>["Joe", "Justin"]}}]

Running over counters with the 'legacy_counter' arg turned on verified that for a non-legacy counter you'll just get 0:

irb(main):068:0> mr.query.first.arg = 'legacy_counter'
=> "legacy_counter"
irb(main):069:0> mr.run
=> [0]
irb(main):070:0> mr.query.first.arg = nil
=> nil
irb(main):071:0> mr.run
=> [{"type"=>"counter", "value"=>13}]

Other than the missing functionality, this works as advertised. 👍

[russelldb]

I see what you mean (re MR wrappers.) The main aim here was to not break existing code, and provide similar support for migrating existing code to 2.0 data types. I'll try and add some funs to riak_kv_mapreduce as time permits though.

Thanks!