将CouchDB的javascript视图转换为erlang

问题描述

我需要一些帮助，将以下CouchDB视图从javascript转换为erlang。我需要它们在erlang，因为在javascript视图使用所有可用的堆栈内存和崩溃couchjs（请参阅这个bugreport ）。

I need some help with translating the following CouchDB views from javascript to erlang. I need them in erlang, because in javascript the view uses all of the available stack memory and crashes couchjs (see this bugreport https://issues.apache.org/jira/browse/COUCHDB-893).

我在javascript中的当前地图功能是：

The current map functions I have in javascript are:

sync / transaction_keys

function(doc) {
  if(doc.doc_type == "Device") {
      for(key in doc.transactions)
          emit(key, null);
  }
}

和同步/转录

function(doc) {
  if(doc.doc_type == "Device") {
      for(key in doc.transactions) {
          t = doc.transactions[key];
          t.device = doc.device;
          emit(key, t);
     }
  }
}

一个示例文档将是：

{
   "_id": "fcef7b5c-cbe6-31af-8363-2b446a7e4cf2",
   "_rev": "3-c90abd075404a75744fd3e5e4f04ebad",
   "device": "fcef7b5c-cbe6-31af-8363-2b446a7e4cf2",
   "doc_type": "Device",
   "transactions": {
       "79fe8630-c0c0-30c6-9913-79b2f93e3e6e": {
           "timestamp": 1309489169533,
           "version": 10008,
           "some_more_data" : "more_data"
       }
       "e4678930-c465-76a6-8821-75a3e888765a": {
           "timestamp": 1309489169533,
           "version": 10008,
           "some_more_data" : "more_data"
       }
   }
}

基本上sync / transaction_keys发出事务字典和同步/事务的所有键都会发出事务字典中的所有条目。

Basically sync/transaction_keys emits all keys of the transaction dictionary and sync/transaction does emit all entries in the transaction dictionary.

不幸的是，我从来没有使用过Erlang d很快就重写这个代码，所以任何帮助都是非常受欢迎的。

Unfortunately I never used Erlang before and I need to rewrite that code pretty soon, so any help is very welcomed.

提前感谢。

推荐答案

我刚刚做了你的第二个（越复杂的一个）。第一个可以从那里轻松推断：

I just did your second one (the more complicated one). The first can easily be extrapolated from there:

fun({Doc}) ->
        %% Helper function to get a toplevel value from this doc.
        F = fun(B) -> proplists:get_value(B, Doc) end,
        %% switch on doc type
        case F(<<"doc_type">>) of
            <<"Device">> ->
                %% Grab the transactions from this document
                {Txns} = F(<<"transactions">>),
                lists:foreach(fun({K,V}) ->
                                      %% Emit the key and the value as
                                      %% the transaction + the device
                                      %% id
                                      {T} = proplists:get_value(K, Txns),
                                      Emit(K, {[{<<"device">>, F(<<"device">>)} | T]})
                              end,
                             Txns);
            _ -> false %% Not a device -- ignoring this document
        end
end.

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