First commit.

.gitignore

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+*.gem
+.bundle
+Gemfile.lock
+pkg/*

.rvmrc

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+rvm use ruby-1.9.2-p0@mongoid_to_csv

Gemfile

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+source "http://rubygems.org"
+
+# Specify your gem's dependencies in mongoid_to_csv.gemspec
+gemspec

README.rdoc

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+= Mongoid.to_csv
+
+== Description
+
+A simple Mongoid::Base to_csv() class method that preserves scopes.
+to_csv() returns the entire contents including the header ready to be written to file.
+
+== Usage
+
+  # Assuming a Movie model with title and director_id columns.
+  Movie.to_csv
+  # would return:
+  title,director_id
+  title,director_id
+  Black Swan,0
+  Inception,1
+  The Fighter,2
+  The King's Speech,3
+  The Kids Are All Right,4
+
+  Movie.bad.to_csv
+  # would return:
+  title,director_id
+  The Kids Are All Right,4
+
+Note that #to_csv is called like a scope or query. The following will NOT give you the same results:
+
+  Movie.all.to_csv
+
+This will use Ruby's Array#to_csv method.
+
+=== Attribute#to_csv
+
+After a model object's attributes are collected, to_csv is called on the resulting array. However, this poses a problem because it will blindly convert the attributes to a string -- i.e. call to_s on them. If one of your attributes is a Date, then calling to_s may produce unwanted output. For example, if you have Date::DATE_FORMATS[:default] = '%d %B, %Y' your dates will have the month written out like 'January', 'February', etc. To counter this, this gem will make an attempt to call to_csv() on each attribute. To get YYYY-MM-DD output, you could do something like:
+
+  class Date
+    def to_csv
+      strftime('%Y-%m-%d')
+    end
+  end
+
+Note that object.send(attribute_name) is used, so datetime fields will be returned as ActiveSupport::TimeWithZone objects.
+
+== TODO
+
+* Options to specify columns to be included (currently, id and timestamp columns are excluded).
+* Combine with active_record_to_csv somehow since they are essentially doing the same thing.
+
+== Compatibility
+
+Tested with Mongoid v2.0.2
+
+http://gem-testers.org/gems/mongoid_to_csv
+
+== Related gems
+
+* https://github.com/ordinaryzelig/mongoid_csv
+* https://github.com/ordinaryzelig/orm_from_csv
+* https://github.com/ordinaryzelig/active_record_to_csv

Rakefile

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+require 'bundler'
+Bundler::GemHelper.install_tasks

lib/mongoid_to_csv.rb

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+require 'mongoid'
+require 'csv'
+
+module MongoidToCSV
+  # Return full CSV content with headers as string.
+  # Defined as class method which will have chained scopes applied.
+  def to_csv
+    csv_columns = fields.keys - %w{_id created_at updated_at _type}
+    header_row = csv_columns.to_csv
+    records_rows = all.map do |record|
+      csv_columns.map do |column|
+        value = record.send(column)
+        value = value.to_csv if value.respond_to?(:to_csv)
+        value
+      end.to_csv
+    end.join
+    header_row + records_rows
+  end
+end
+
+module Mongoid::Document
+  def self.included(target)
+    target.extend MongoidToCSV
+  end
+end
+
+# Define Relation#to_csv so that method_missing will not
+# delegate to array.
+class Mongoid::Relation
+  def to_csv
+    scoping do
+      @klass.to_csv
+    end
+  end
+end

lib/mongoid_to_csv/version.rb

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+module MongoidToCSV
+  VERSION = "0.1.0"
+end

mongoid_to_csv.gemspec

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+# -*- encoding: utf-8 -*-
+$:.push File.expand_path("../lib", __FILE__)
+require "mongoid_to_csv/version"
+
+Gem::Specification.new do |s|
+  s.name        = "mongoid_to_csv"
+  s.version     = MongoidToCSV::VERSION
+  s.platform    = Gem::Platform::RUBY
+  s.authors     = ["Jared Ning"]
+  s.email       = ["[email protected]"]
+  s.homepage    = "https://github.com/ordinaryzelig/mongoid_to_csv"
+  s.summary     = %q{Simple Mongoid Model to_csv() class method that preserves scopes}
+  s.description = %q{Simple Mongoid Model to_csv() class method that preserves scopes}
+
+  s.rubyforge_project = "mongoid_to_csv"
+
+  s.files         = `git ls-files`.split("\n")
+  s.test_files    = `git ls-files -- {test,spec,features}/*`.split("\n")
+  s.executables   = `git ls-files -- bin/*`.split("\n").map{ |f| File.basename(f) }
+  s.require_paths = ["lib"]
+
+  s.add_dependency 'mongoid', '>= 2.0.0.rc.7'
+
+  s.add_development_dependency 'rspec', '2.6.0'
+  s.add_development_dependency 'mongo', '>= 1.3.1'
+  s.add_development_dependency 'bson_ext'
+end

spec/database.rb

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+# Initialize/connect.
+host = 'localhost'
+port = Mongo::Connection::DEFAULT_PORT
+database_name = 'mongoid_to_csv'
+connection = Mongo::Connection.new(host, port)
+# Drop database if it exists.
+connection.drop_database(database_name)
+db = connection.db(database_name)
+Mongoid.database = db

spec/mongoid_to_csv_spec.rb

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+require 'spec_helper'
+
+describe MongoidToCSV do
+
+  before :all do
+    [
+      'Black Swan',
+      'Inception',
+      'The Fighter',
+      "The King's Speech",
+      'The Kids Are All Right'
+    ].each_with_index do |title, i|
+      Movie.create!(
+        :title => title,
+        :released_on => Date.new(2010, 1, i + 1)
+      )
+    end
+  end
+
+  it 'should convert records to csv' do
+    Movie.to_csv.should eq(content_of(fixtures_file('movies.csv')))
+  end
+
+  it' should preserve scope' do
+    Movie.bad.to_csv.should eq(content_of(fixtures_file('movies_bad.csv')))
+  end
+
+  it 'should not include id and timestamp fields' do
+    header = Movie.to_csv.lines.first
+    header.should_not =~ /^id|created_at|updated_at/
+  end
+
+  it 'should call to_csv on each attribute if it responds to it' do
+    date = Movie.limit(1).first.released_on
+    csv_string = Movie.limit(1).to_csv
+    csv_string.should include(date.to_csv)
+    csv_string.should_not include(date.to_s)
+  end
+
+end

spec/spec_helper.rb

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+require 'pathname'
+
+require File.join(Pathname(__FILE__).dirname.expand_path, '../lib/mongoid_to_csv')
+
+require 'database'
+
+# require support .rb files.
+Dir[File.expand_path("../support/**/*.rb", __FILE__)].each {|f| require f}
+
+RSpec.configure do |config|
+  config.include Macros
+end

spec/support/fixtures/movies.csv

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+title,released_on
+Black Swan,2010/01/01
+Inception,2010/01/02
+The Fighter,2010/01/03
+The King's Speech,2010/01/04
+The Kids Are All Right,2010/01/05

spec/support/fixtures/movies_bad.csv

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+title,released_on
+The Kids Are All Right,2010/01/05

spec/support/macros.rb

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+module Macros
+
+  def content_of(file)
+    file.read
+  end
+
+  def fixtures_file(file_name)
+    File.open(File.join(Pathname(__FILE__).dirname.expand_path, 'fixtures', file_name))
+  end
+
+end

spec/support/models/date.rb

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+class Date
+  def to_csv
+    strftime('%Y/%m/%d')
+  end
+end

spec/support/models/movie.rb

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+class Movie
+
+  include Mongoid::Document
+
+  field :title
+  field :released_on, type: Date
+  include Mongoid::Timestamps
+
+  scope :bad, where(:title  => 'The Kids Are All Right')
+
+end