On 16 November 2016 at 17:40, Vikram Lalit <vikramla...@gmail.com> wrote:
> Hi - I am trying to leveraging CRDT sets to store chat messages that my > distributed Riak infrastructure would store. Given the intrinsic > conflict-resolution, I thought this might be more beneficial than me > putting together a merge implementation based on the causal context. > > However, my data model requires each chat message to be associated to > something like a post, hence I was thinking of having the post reference as > the bucket, and chat references as keys in that bucket. With of course the > bucket-type datasource equated to 'set'. Unfortunately though, from the > documentation, I'm not able to ascertain how to associate a created set > with an existing bucket and a new key reference if I use the Erlang client. > This seems possible for other languages but not for Erlang, with the Basho > doc mentioning "%% Sets in the Erlang client are opaque data structures > that collect operations as you mutate them. We will associate the data > structure > with a bucket type, bucket, and key later on.". > > Subsequent code only seems to fetch the set from the bucket / key but > where exactly is the allocation happening? > > {ok, SetX} = riakc_pb_socket:fetch_type(Pid, {<<"sets">>,<<"travel">>}, << > "cities">>). > > Perhaps I'm missing something, or is there a code snippet that I can > leverage? > > Thanks! > > Hi Vikram, Please have a look at the following snippet, that shows the complete set of operations used to update a CRDT set with the Erlang client: update_crdt_set(Server, BType, Bucket, Key, Val) -> T = unicode:characters_to_binary(BType), B = unicode:characters_to_binary(Bucket), K = unicode:characters_to_binary(Key), {ok, Pid} = riakc_pb_socket:start_link(Server, 8087), Set = case riakc_pb_socket:fetch_type(Pid, {T, B}, K) of {ok, O} -> O; {error, {notfound, set}} -> riakc_set:new() end, Set1 = riakc_set:add_element(unicode:characters_to_binary(Val), Set), {ok, {set, Vals, _Adds, _Dels, _Ctx}} = riakc_pb_socket:update_type( Pid, {T, B}, K, riakc_set:to_op(Set1), [return_body]), Vals. The set is updated with riakc_set:add_element/2, and sent back to the server with riakc_pb_socket:update_type/5, which in turn takes an argument returned from riakc_set:to_op/1. More information and samples can be found in the Riak documentation [0] and the Riak Erlang client API docs [1][2]. Please let me know if this answered your question. Kind Regards, Magnus [0]: http://docs.basho.com/riak/kv/2.1.4/developing/data-types/sets/ [1]: https://basho.github.io/riak-erlang-client/riakc_set.html [2]: https://basho.github.io/riak-erlang-client/riakc_pb_socket.html#update_type-5 -- Magnus Kessler Client Services Engineer Basho Technologies Limited Registered Office - 8 Lincoln’s Inn Fields London WC2A 3BP Reg 07970431
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