map_function.js

function(doc) {
  if ( doc["couchrest-type"] == "Account" ) {
    emit(doc._id, ["Account", doc]);
  }
  if ( doc["couchrest-type"] == "Contact" ) {
    emit(doc.account_id, ["Contact", doc]);
  }
}

reduce_function.js

function(account_id, results, rereduce) {
  contacts = [];
  var account;
  
  if( rereduce ) {
    return results;
  } else {

    for(var i=0; i< results.length; i++){
      if( results[i][0] == "Contact" ){
        contacts.push(results[i][1]);
      }
      if ( results[i][0] == "Account" ) {
        account = results[i][1];
      }
    }
    if(account) {
      account.contacts = contacts;
      return account;
    } else { return null; }
  }
}