How to rename a column in a collection in Mongodb using MongoMapper? - mongodb

Question

Mongodb gives an option for renaming a column name as follows
db.collection.update({},{'$rename'=> {'old_name' => 'new_name'}}, false,true)
Is it possible for using MongoMapper to do the same? The documentation doesn't specify anything.
I also tried getting the Mongodb connection handle from MongoMapper as
connection = MongoMapper.connection
db = MongoMapper.database
collection = db.collection('collection_name')
collection .update(....)
and doing the same query but it doesn't work.

Answer 1

MongoMapper uses the 10gen Ruby driver, and MongoMapper::Document provides access to the underlying driver objects.
The following working test shows that you can use Model.collection.update to do what you want, to rename a field for the model 'Model'. Make sure to use the :multi => true option to update if you want to update/rename more than a single document.
app/models/model.rb
class Model
include MongoMapper::Document
end
test/unit/model_test.rb
require 'test_helper'
class ModelTest < ActiveSupport::TestCase
def setup
Model.remove
end
test "rename" do
puts "Model.collection.class: #{Model.collection.class}"
puts "Model.database.class: #{Model.database.class}"
Model.create( 'old_name' => 'name value 0', 'another_key' => 'another value 0' )
Model.create( 'old_name' => 'name value 1', 'another_key' => 'another value 1' )
assert_equal(2, Model.where( 'old_name' => { '$exists' => true } ).count)
Model.collection.update( {}, { '$rename' => { 'old_name' => 'new_name' } }, :multi => true )
assert_equal(0, Model.where( 'old_name' => { '$exists' => true } ).count)
p Model.all
end
end
$ rake test
Rack::File headers parameter replaces cache_control after Rack 1.5.
Run options:
# Running tests:
Model.collection.class: Mongo::Collection
Model.database.class: Mongo::DB
[DEPRECATED] The 'safe' write concern option has been deprecated in favor of 'w'.
[#<Model _id: BSON::ObjectId('5101809d7f11ba1256000001'), another_key: "another value 0", new_name: "name value 0">, #<Model _id: BSON::ObjectId('5101809d7f11ba1256000002'), another_key: "another value 1", new_name: "name value 1">]
.
Finished tests in 0.012344s, 81.0110 tests/s, 162.0220 assertions/s.
1 tests, 2 assertions, 0 failures, 0 errors, 0 skips