I was expecting some really tricky code, but it's just simple and clean. Thanks a lot. My links point to objects in the same bucket, so I'll store an array of object keys and I'll add the bucket name directly in the map function.
I did not find any doc about preloading javascript functions. Is it the same as storing JS files in a bucket and load them thanks to the "bucket" and "key" fields, as described in the "Map" paragraph of the Fast Track ? https://wiki.basho.com/display/RIAK/Loading+Data+and+Running+MapReduce+Queries -Nicolas On Sun, Jul 11, 2010 at 12:20 AM, Bryan Fink <br...@basho.com> wrote: > On Sat, Jul 10, 2010 at 4:45 PM, Nicolas Fouché <nico...@silentale.com> wrote: >> In the "one-to-very-many link associations" thread , Sean Cribbs talks >> about a map function which does link-walking from links stored in >> object contents. http://bit.ly/cKguqQ >> >> "Another way to cope with large numbers of links is to >> encapsulate them in the object itself, rather than in the headers. This >> removes >> the header-length/count limitation, but would require you to have a map >> function >> that understands the internals of the object. Also, you would need to deal >> with >> the larger size of the object, which could potentially slow down your >> request." >> >> Is there any chance someone shares the code of a map function doing >> this (custom-)link-walking ? > > Hi, Nicolas. Any function you have that returns a list of bucket-key > pairs, in the same format as the "inputs" list for the map/reduce > query, will work. For example, if you stored your object's links in a > "mylinks" field in it's value, like so: > > $ curl -X PUT -H "content-type:application/json" > http://localhost:8098/riak/example/foo --data @- > {"mylinks":[["example","bar"],["example","baz"]],"myval":1} > ^D > $ curl -X PUT -H "content-type:application/json" > http://localhost:8098/riak/example/bar --data @- > {"mylinks":[["example","baz"]],"myval":2} > ^D > $ curl -X PUT -H "content-type:application/json" > http://localhost:8098/riak/example/baz --data @- > {"mylinks":[["example","foo"]],"myval":3} > ^D > > Then you could use a very simple map function like: > function(v) { > return v.not_found ? [] : JSON.parse(v.values[0].data).mylinks; > } > > And then the link-walking is simple: > > carboy:riak bryan$ curl -X POST -H "content-type:application/json" > http://localhost:8098/mapred --data @- > {"inputs":[["example","foo"]],"query":[{"map":{"language":"javascript","source":"function(v) > { return v.not_found ? [] : JSON.parse(v.values[0].data).mylinks; > }"}},{"map":{"language":"javascript","source":"function(v) { return > [JSON.parse(v.values[0].data).myval]; }"}}]} > ^D > [2,3] > > That query uses two map phases to start at the example/foo object I > created above, and then follow the links it has to the example/bar and > example/baz, and extracting the "myval" field from the values of those > objects. > > I'd recommend adding a little defensive programming in to make sure > that "mylinks" is defined, and that it's a list of the proper shape. > It would also be a good idea to define these function in a file that > Riak would preload, instead of specifying them dynamically in the > query (for performance). But, you could also take it in another > direction: if you knew that all of your links were going to point to > objects in a certain bucket, you could store just the keys in the > object, and produce bucket-key pairs with a quick map function (e.g. > mykeys.map(function(k) { return ["otherbucket", k]; }) > > Hope that helps. > > -Bryan > _______________________________________________ riak-users mailing list riak-users@lists.basho.com http://lists.basho.com/mailman/listinfo/riak-users_lists.basho.com
