Translate couchdb replication filter from javascript to erlang

Question

I have a replication filter in JavaScript which is running too slowly, and it was suggested that I try re-writing it in erlang.

I've set up the environment, and am able to successfully execute simple erlang views in the futon "temp_view" dialog, but I'm not having any luck translating my JavaScript function to erlang.

Can anyone suggest how the following might best be re-written in erlang? Any help would be greatly appreciated.

function(doc, req) {
    if (doc.date && doc.user_id && (doc.user_id == req.query.userid) && (doc._id.indexOf(\"_design\") != 0)){
        var doc_month = "" + doc.date[1];
        if(doc_month.length == 1) {
            doc_month = "0" + doc_month;
        }
        var doc_day = "" + doc.date[2];
        if(doc_day.length == 1) {
            doc_day = "0" + doc_day;
        }
        var req_month = "" + req.query.month;
        if(req_month.length == 1) {
            req_month = "0" + req_month;
        }
        var req_day = "" + req.query.day;
        if(req_day.length == 1) {
            req_day = "0" + req_day;
        }
        var doc_datestring = doc.date[0] + "-" + doc_month + "-" + doc_day;
        var req_datestring = req.query.year + "-" + req_month + "-" + req_day;

        return (doc_datestring >= req_datestring);
    } else {
        return false;
    }
}

score 1 · Accepted Answer · answered Jan 10 '13 at 00:39

I just finished writing something that I believe is similar to your javascript function. I have a year and a month field in my documents - both represented as integers.

This is what I ended up with:


{
   "_id": "_design/fast_segmenting",
   "language": "erlang",
   "filters": {
       "by_year_month": "... see below for erlang function ..."
   }
}

Kind of ugly, so here is the Erlang filter function in a better format:


fun({Doc}, {Req}) -> 
    {Query} = proplists:get_value((<<\"query\">>, Req), 
    Month = list_to_integer(binary_to_list(proplists:get_value((<<\"month\">>, Query))), 
    Year = list_to_integer(binary_to_list(proplists:get_value((<<\"year\">>, Query))), 

    case {proplists:get_value((<<\"pubMonth\">>, Doc), proplists:get_value((<<\"pubYear\">>, Doc)} of 
        {Month, Year} -> true; 
        _ -> false 
    end 
end.

The most fun was discovering that the values in the Query object are binaries in Erlang, which is why we need to convert them to integers.

Translate couchdb replication filter from javascript to erlang

1 Answers1