How to use js libs (like underscorejs) in your CouchDB views

Sometimes, in CouchDB you have to do some data manipulation in the map/reduce functions, that involves array manipulation, summing timestamps, grouping and so on.

But CouchDB doesn’t offer a native way to do that. So you have to code all by your bare hands, like this:

//SOME DATA
var array = ["Juan", "Marisa", "James", "Juan", "Marcos"];

//CODE FOR GROUPING
result = {};
//BASICALLY YOU ITERATES OVER AN ARRAY
for(a in array){
  //IF THE INDEX IS ALREADY IN THE RESULT OBJECT, JUST ADD ONE
  if(result[array[a]])result[array[a]]++;
  //ELSE , YOU ADD A NEW ENTRY IN THE RESULT OBJECT
  else result[array[a]]=1;
}

//AT THIS POINT YOU HAVE THE RESULT OBJECT FILLED WITH PAIRS
/*
{
  "Juan" : 2,
  "Marisa" : 1, 
  "James": 1
  "Marcos": 1
}
*/

But this is not usual nowadays, where you have so many production-ready js libraries like underscorejs to do all the hard work for you.

When I faced this problem at the first time I found only 1 post that have mentioned it (CommonJS Modules in CouchDB by Caolan McMahon) which explains how to use this feature (Since version 1.1, it offers a way to use CommonJS 1.0 modules) in a CouchDB Database.

I just simply  picked up the whole minified source of underscorejs and pasted in the design document/ views / lib / libname  field of the design document that I want.

It will be like this:

UnderscoreJS lib in CouchDB

You can do this with any library you want, since it follows the CommonJS Modules Specification.

And the code above in the post will be:

function(doc) {
  //IMPORTING THE LIB
  var _ = require("views/lib/underscorejs");
  //MOCKING DATA
  var array = ["Juan", "Marisa", "James", "Juan", "Marcos"];

  //INSTEAD OF DOING MANUAL OPERATIONS I SIMPLY CALL:
  var grouped = _.countBy(array, function(i){
      return i;
  });

  //AT THIS POINT YOU HAVE THE RESULT OBJECT FILLED WITH PAIRS 
  /* 
     { 
       "Juan" : 2, 
       "Marisa" : 1, 
       "James": 1, 
       "Marcos": 1 } 
  */

  //THAT YOU CAN EMIT TO REDUCE LIKE THIS.
  emit(doc._id, grouped); 
}

A print showing the result:

A Map function with UnderscoreJS

Another example is the momentjs lib, it can be helpful when you need to do some date/time manipulation.

But there are 2 issues in this feature:

#1 –  You can’t import the libs in the reduce function;

#2 – Like Caolan said, there’s still no support for caching of evaluated modules, that means require a module will be evaluated every time (a bit inneficient);

That’s it for now, please leave comments if you know some related techniques or alternatives for importing libs in CouchDB.

Resources:

CouchDB CommonJS Modules

CommonJS Module Specification 10.0

Jira Ticket about the second issue