I'm experimenting with Riak by trying to port a simple a/b testing framework
that's currently SQL backed. Since I'm using Ripple/riak-client my code
below are in Ruby/JS.
The domain model is fairly simple. I have visitors, which get created for
any user who hits the site, visitors see alternatives (currently these are
ActiveRecord objects) and are tracked by creating experiences (the joining
of a alternative ID and a visitor). Finally, as visitors do things we track
events, which are distinguished from one another by their classes.
Here is a simplified version of the model code:
class Riak::Visitor
include Ripple::Document
many :events, :class_name => "Riak::Event"
end
class Riak::Event
include Ripple::Document
end
class Riak::ShareEvent < Riak::Event
include Ripple::Document
end
class Riak::Experience
include Ripple::Document
one :visitor, :class_name => "Riak::Visitor"
property :alternative_id, Integer, :presence => true
end
My problem is that I'd like to collect the set of visitors who have shared,
or more generally I'd like to return a set of visitors after narrowing down
the list by linking in specific kind of events. Well, my real problem is
that I still don't quite grok MapReduce, but this is what I'm trying to
accomplish.
The riak-client code is included below (see visitors_who_shared). It returns
a list of all visitors found in the map phase where keep is true. This isn't
surprising, but I'm not sure how to get the visitors if I don't “keep” them
in that phase.
Thanks in advance for any help. I'm also happy RTFM and would appreciate
specific suggestions for doing nontrivial MR jobs in JavaScript.
class Riak::Alternative #not a riak doc
attr_accessor :ar_id
def initialize(ar_id)
self.ar_id = ar_id
end
def visitors_who_shared
Riak::MapReduce.new(Ripple.client).
add("riak_experiences").
map(map_filter_by_alternative).
link(:bucket => 'riak_visitors', :keep => true).
link(:bucket => 'riak_events').
map("function(v){ return [[v.bucket, v.key]]; }").
map(map_share_events).
run
end
def map_share_events
f = <<FUNCTION
function(v){
var data = JSON.parse(v.values[0].data);
if(data._type != "Riak::ShareEvent" ){
return [];
}else{
return [[v.bucket, v.key]];
}
}
FUNCTION
end
def map_filter_by_alternative
f = <<FUNCTION
function(v){
var data = JSON.parse(v.values[0].data);
if(data.alternative_id != #{self.ar_id} ){
return [];
}else{
return [[v.bucket, v.key]];
}
}
FUNCTION
end
end
Riak::Alternative.new(1).visitors_who_shared
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