Nested content_tag throws undefined method `output_buffer=` in simple helper - ruby-on-rails-3

Question

I'm trying to create a simple view helper but as soon as I try nest a couple of content tags it will throw NoMethodError: undefined method `output_buffer=' for
def table_for(list, &proc)
t = Table.new
proc.call(t)
t.render_column(list)
end
class Table
include ActionView::Helpers::TagHelper
attr_accessor :columns, :block
def initialize
#columns = Array.new
end
def col(name)
#columns << name
end
def render_column(list)
content_tag :table do
list.each do |c|
content_tag :td, c
end
end
end
end
Any hints of what's wrong? I've also seen that there's a XmlBuilder is that one better for my purpose?

Answer 1

ActionView::Base has built into it the Context module, which provides the methods output_buffer() and output_buffer=().
So you can solve your problem either by having your class do:
include ActionView::Context
Or even more simply:
attr_accessor :output_buffer

Answer 2

I think there were some changes about this in 3.0, but in previous versions the trick was to pass self:
def table_for(list, &proc)
Table.new(self)
# ...
def initialize(binding)
#binding = binding
#...
def render_column
#binding.content_tag :table do
# ...
end
end
I'm not sure if this is still how it's done in rails 3.
Another thing to fix in ordere for the code to work is to save the output of the inner content_tag somewhere, as with each the content is generated and then discarded. One of the possible solutions:
def render_column(list)
#binding.content_tag :table do
list.inject "" do |out, c|
out << #binding.content_tag(:td, c)
end.html_safe
end
end

Answer 3

With help from Nested content_tag throws undefined method `output_buffer=` in simple helper I ended up with the following solution inspired by the API for Formtastic.
<%= table_for(#users) do |t| %>
<% t.col :name %>
<% t.col :email %>
<% t.col :test, :value => lambda { |u| u.email }, :th => 'Custom column name' %>
<% t.col :static, :value => 'static value' %>
<% end %>
Using the output_buffer directly and probably reinventing the wheel the code looks like
module ApplicationHelper
def table_for(list, &block)
table = Table.new(self)
block.call(table)
table.show(list)
end
class Column
include ActiveSupport::Inflector
attr_accessor :name, :options
def initialize(name, options = {})
#name = name
#options = options
end
def td_value(item)
value = options[:td]
if (value)
if (value.respond_to?('call'))
value.call(item)
else
value
end
else
item[name]
end
end
def th_value
options[:th] ||= humanize(name)
end
end
class Table
include ActionView::Helpers::TagHelper
attr_accessor :template, :columns
def initialize(temp)
#columns = Array.new
#template = temp
end
def col(name, options = {})
columns << Column.new(name, options)
end
def show(list)
template.content_tag(:table) do
template.output_buffer << template.content_tag(:tr) do
columns.collect do |c|
template.output_buffer << content_tag(:th, c.th_value)
end
end
list.collect do |item|
template.output_buffer << template.content_tag(:tr) do
columns.collect do |c|
template.output_buffer << template.content_tag(:td, c.td_value(item))
end
end
end
end
end
end
end