callbacks and returns with CouchDB and nano.js

Question

I'm trying to write a small library with re-usable database calls with nano.

db.view('list', 'people', function(error, data) {
  if (error == null) {
    res.render('people/index', {
      people: data.rows
    });
  } else {
    // error
  }
});

That can get quite messy when having multiple requests:

db.view('list', 'people', function(error, people) {
  db.view('list', 'items', function(error, items) {
    db.view('list', 'questions', function(error, questions) {
      db.view('list', 'answers', function(error, answers) {
        ...
        res.render('people/index', {
          people: people.rows,
          items: items.rows,
          questions: questions.rows
          ...

So, the idea was to create a function:

var getPeople = function() {
  // do db calls here and return
}

res.render('people/index', {
  people: getPeople()
});

But that doesn't work.

How can I solve this and put everything into an external node-js-module.js file?

Answer 1

You got some great answers here already.

From the nano source code you have an example that might help:

• https://github.com/dscape/nano/blob/master/examples/bulk_transform.js

Also if you don't really understand how nodejs flow control works I can't recommend enough that you see this tutorial:

• http://nodetuts.com/tutorials/19-asynchronous-iteration-patterns.html#video

Better than using a tool is to use the tool understanding how it works :) Maybe you'll end up just coding your own control flow, that's what most of us ends up doing anyway.

Hope this helps, attached code for convenience.

  var db    = require('nano')('http://localhost:5984/emails')
    , async = require('async')
    ;

  function update_row(row,cb) {
    var doc = row.doc;
    delete doc.subject;
    db.insert(doc, doc._id, function (err, data) {
      if(err)  { console.log('err at ' + doc._id);  cb(err); }
      else     { console.log('updated ' + doc._id); cb(); }
    });
  }

  function list(offset) {
    var ended = false;
    offset = offset || 0;
    db.list({include_docs: true, limit: 10, skip: offset}, 
      function(err, data) {
        var total, offset, rows;
        if(err) { console.log('fuuuu: ' + err.message); rows = []; return; }
        total  = data.total_rows;
        offset = data.offset;
        rows   = data.rows;
        if(offset === total) { 
          ended = true;
          return; 
        }
        async.forEach(rows, update_row, function (err) {
          if(err) { console.log('something failed, check logs'); }
          if(ended) { return; }
          list(offset+10);
        });
    });
  }

  list();