Comma is a CSV (ie. comma separated values) generation extension for Ruby objects, that lets you seamlessly define a CSV output format via a small DSL. Comma works well on pure Ruby objects with attributes, as well as complex ones such as ActiveRecord objects with associations, extensions, etc. It doesn’t distinguish between attributes, methods, associations, extensions, etc. - they all are considered equal and invoked identically via the Comma DSL description. Multiple different CSV output descriptions can also be defined.
When multiple objects in an Array are converted to CSV, the output includes generation of a header row reflected from names of the properties requested, or specified via the DSL.
CSV can be a bit of a boring format - the motivation behind Comma was to have a CSV extension that was simple, flexible, and would treat attributes, methods, associations, etc., all the same without the need for any complex configuration, and also work on Ruby objects, not just ActiveRecord or other base class derivatives.
An example Comma CSV enabled ActiveRecord class:
class Book < ActiveRecord::Base # ================ # = Associations = # ================ has_many :pages has_one :isbn belongs_to :publisher # =============== # = CSV support = # =============== comma do name description pages :size => 'Pages' publisher :name isbn :number_10 => 'ISBN-10', :number_13 => 'ISBN-13' blurb 'Summary' end end
Annotated, the comma description is as follows:
# starts a Comma description block, generating 2 methods #to_comma and # #to_comma_headers for this class. comma do # name, description are attributes of Book with the header being reflected as # 'Name', 'Description' name description # pages is an association returning an array, :size is called on the # association results, with the header name specified as 'Pages' pages :size => 'Pages' # publisher is an association returning an object, :name is called on the # associated object, with the reflected header 'Name' publisher :name # isbn is an association returning an object, :number_10 and :number_13 are # called on the object with the specified headers 'ISBN-10' and 'ISBN-13' isbn :number_10 => 'ISBN-10', :number_13 => 'ISBN-13' # blurb is an attribute of Book, with the header being specified directly # as 'Summary' blurb 'Summary' end
In the above example, any of the declarations (name, description, pages, publisher, isbn, blurb, etc), could be methods, attributes, associations, etc - no distinction during configuration is required, as everything is invoked via Ruby’s #send method.
You can get the CSV representation of any object by calling the to_comma method, optionally providing a CSV description name to use.
Object values are automatically converted to strings via to_s allowing you to reuse any existing to_s methods on your objects (instead of having to call particular properties or define CSV specific output methods). Header names are also automatically humanized when reflected (eg. Replacing _ characters with whitespace). The ‘isbn’ example above shows how multiple values can be added to the CSV output.
Multiple CSV descriptions can also be specified for the same class, eg:
class Book < ActiveRecord::Base # ================ # = Associations = # ================ has_many :pages has_one :isbn belongs_to :publisher # =============== # = CSV support = # =============== comma do name description pages :size => 'Pages' publisher :name isbn :number_10 => 'ISBN-10', :number_13 => 'ISBN-13' blurb 'Summary' end comma :brief do name description blurb 'Summary' end end
You can specify which output format you would like to use via an optional parameter to to_comma:
Book.limited(10).to_comma(:brief)
Specifying no description name to to_comma is equivalent to specifying :default as the description name.
You can pass options for FasterCSV, e.g.
Book.limited(10).to_comma(:style => :brief, :col_sep => ';', :force_quotes => true)
You can pass the :filename option and have Comma writes the CSV output to this file:
Book.limited(10).to_comma(:filename => 'books.csv')
For more complex relationships you can pass blocks for calculated values, or related values. Following the previous example here is a comma set using blocks (both with and without labels for your CSV headings):
class Publisher < ActiveRecord::Base # ================ # = Associations = # ================ has_one :primary_contact, :class_name => "User" #(basic user with a name) has_many :users end class Book < ActiveRecord::Base # ================ # = Associations = # ================ has_many :pages has_one :isbn belongs_to :publisher # =============== # = CSV support = # =============== comma do name description pages :size => 'Pages' publisher :name publisher { |publisher| publisher.primary_contact.name.to_s.titleize } publisher 'Number of publisher users' do |publisher| publisher.users.size end isbn :number_10 => 'ISBN-10', :number_13 => 'ISBN-13' blurb 'Summary' end end
In the preceding example, the 2 new fields added (both based on the publisher relationship) mean that the following will be added:
- the first example 'publishers_contact' is loaded straight as a block. The value returned by the lambda is displayed with a header value of 'Publisher' - the second example 'total_publishers_users' is sent via a hash and a custom label is set, if used in the first examples method the header would be 'Publisher', but sent as a hash the header is 'Number of publisher users'.
When used with Rails (ie. add ‘comma’ as a gem dependency), Comma automatically adds support for rendering CSV output in your controllers:
class BooksController < ApplicationController def index respond_to do |format| format.csv { render :csv => Book.limited(50) } end end end
You can specify which output format you would like to use by specifying a style parameter:
class BooksController < ApplicationController def index respond_to do |format| format.csv { render :csv => Book.limited(50), :style => :brief } end end end
When used with Rails 2.3.*, Comma also adds support for exporting named scopes:
class Book < ActiveRecord::Base named_scope :recent, lambda { { :conditions => ['created_at > ?', 1.month.ago] } } # ... end
Calling the to_comma method on the named scope will internally use Rails’ find_each method, instantiating only 1,000 ActiveRecord objects at a time:
Book.recent.to_comma
If you’re on Ruby 1.8.*, the FasterCSV gem is recommended for performance reasons.
gem install fastercsv
If you have any questions or suggestions for Comma, please feel free to contact me at crafterm@redartisan.com, all feedback welcome!