CODEWITHSUNDEEP
javascripterlangcouchdb
Colfax
Colfax

Reputation: 177

Translate couchdb replication filter from javascript to erlang

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;
    }
}

Upvotes: 1

Views: 256

Answers (1)

ryan1234
ryan1234

Reputation: 7275

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.

Upvotes: 1

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