README.md in csvbuilder-dynamic-columns-exporter-0.1.0 vs README.md in csvbuilder-dynamic-columns-exporter-0.1.1

@@ -1,33 +1,118 @@
-# Csvbuilder::Dynamic::Columns
+# Csvbuilder::Dynamic::Columns::Exporter
 
-Welcome to your new gem! In this directory, you'll find the files you need to be able to package up your Ruby library into a gem. Put your Ruby code in the file `lib/csvbuilder/dynamic/columns`. To experiment with that code, run `bin/console` for an interactive prompt.
+[Csvbuilder::Dynamic::Columns::Exporter](https://github.com/joel/csvbuilder-dynamic-columns-exporter) is part of the [csvbuilder-collection](https://github.com/joel/csvbuilder)
 
-TODO: Delete this and the text above, and describe your gem
+The Dynamic Columns Exporter contains the implementation for exporting a collection of objects within a variable group as a CSV file.
 
+For instance, any object belonging to categories.
+
 ## Installation
 
 Install the gem and add to the application's Gemfile by executing:
 
-    $ bundle add csvbuilder-dynamic-columns
+    $ bundle add csvbuilder-dynamic-columns-exporter
 
 If bundler is not being used to manage dependencies, install the gem by executing:
 
-    $ gem install csvbuilder-dynamic-columns
+    $ gem install csvbuilder-dynamic-columns-exporter
 
 ## Usage
 
-TODO: Write usage instructions here
+Let's consider a Developer with languages skill.
 
+```ruby
+class UserCsvRowModel
+  include Csvbuilder::Model
+  include Csvbuilder::Export
+
+  column :name, header: "Developer"
+
+  dynamic_column :skills
+
+  def skill(skill_name)
+    source_model.skills.where(name: skill_name).exists? ? "1" : "0"
+  end
+end
+```
+
+For each Row, a method called by the singular version name of the declared Dynamic Columns will be called to determine the cell's value. In our example: `skill` must be implemented in the Exporter Model.
+
+The `source_model` is provided and accessible within this method. In our example, it is the `User`. The File Exporter appends this object to the Row.
+
+The dynamic part of the headers must be provided through the context under the same key name as the declared Dynamic Columns, here `skills`.
+
+```ruby
+context = { skills: ["Ruby", "Python", "Javascript"] }
+
+exporter  = Csvbuilder::Export::File.new(UserCsvExportModel, context)
+
+exporter.headers
+# => ["Developer", "Ruby", "Python", "Javascript"]
+
+sub_context = {} # it merged to the context
+
+exporter.generate do |csv|
+  User.all.each do |user|
+    csv.append_model(user, sub_context) # user here is the source_model.
+  end
+end
+
+exporter.to_s
+# => "Developer,Ruby,Python,Javascript\Bob,1,0,0\n"
+```
+
+## Format Dynamic Columns
+
+Instead of taking care of the formatting directly in the dynamic cell method, here `skill`, it can be delegated to `format_dynamic_column_cells.`
+
+Consider the following rewrite:
+
+```ruby
+class UserCsvRowModel
+  include Csvbuilder::Model
+
+  column :name, header: "Developer"
+
+  dynamic_column :skills
+end
+```
+
+```ruby
+class UserCsvExportModel < UserCsvRowModel
+  include Csvbuilder::Export
+
+  def skill(skill_name)
+    source_model.skills.where(name: skill_name).exists?
+  end
+
+  class << self
+    def format_dynamic_column_cells(cells, _column_name, _context)
+      cells.map do |cell|
+        case cell
+        when true
+          "1"
+        when false
+          "0"
+        else
+          "N/A"
+        end
+      end
+    end
+  end
+
+end
+```
+
 ## Development
 
 After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.
 
 To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and the created tag, and push the `.gem` file to [rubygems.org](https://rubygems.org).
 
 ## Contributing
 
-Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/csvbuilder-dynamic-columns. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the [code of conduct](https://github.com/[USERNAME]/csvbuilder-dynamic-columns/blob/main/CODE_OF_CONDUCT.md).
+Bug reports and pull requests are welcome on GitHub at https://github.com/joel/csvbuilder-dynamic-columns. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the [code of conduct](https://github.com/[USERNAME]/csvbuilder-dynamic-columns/blob/main/CODE_OF_CONDUCT.md).
 
 ## License
 
 The gem is available as open source under the terms of the [MIT License](https://opensource.org/licenses/MIT).