prawn pdf group, transaction and rollback method problems - ruby-on-rails

Question

I'm trying to create a pdf report using prawn in a rails application. There are lots of sections that contain user generated content that I want to try and group together. Sometimes this will go over more that one page which results in a cannot group error. I then tried to use a transaction so that in the event of an error I can rollback and then output the content without using the group method.
The problem is the rollback stuffs up the pages. It removes the extra page from the pdf but still has the wrong page count and outputs over lapping content when I try to redo it. I reset the y position after the rollback, as per the prawn documentation but I still get the problems.
eg. The following test code writes 2 pages of numbers, does a rollback to the start and then tries to write the same numbers again. It results in a single page pdf with the second page of numbers overlapping the first and a page count of 2. The page counts at the bottom of the page also overlap one another even though I'm using the prawn number_pages method
class TestReport < Prawn::Document
def to_pdf
font('Helvetica')
bounding_box([bounds.left, bounds.top - 50], :width => bounds.width, :height => bounds.height - 100) do
text 'begin'
y_pos = y
transaction do
begin
group do
64.times do|i|
text i.to_s
end
end
rescue
rollback
end
end
self.y = y_pos
64.times do|i|
text i.to_s
end
text 'end'
text page_number.to_s
end
page_numbers(1)
#render
end
def page_numbers(start)
string = "page <page> of <total>"
options = { :at => [bounds.right - 150, 40],
:width => 150,
:align => :right,
:start_count_at => start,
:color => "000000" }
number_pages string, options
end
end
def test_report
pdf = TestReport.new()
pdf.to_pdf
send_data pdf.render, filename: "test.pdf",
type: "application/pdf",
disposition: "inline"
end
The problems seem to be with transaction rollbacks. The main thing I want is to be able to use the group method. Is there another way?
Is my code wrong? Am I missing something or do transaction not currently work.
I'm currently using the master prawn branch in a ruby on rails application ( gem 'prawn', :git =>
'git://github.com/prawnpdf/prawn.git', :branch => 'master').

Answer 1

This question is quite old now, but I'll post an answer since it is one of the first hits on Google when searching for the exception.
Transactions still doesnt work with page breaks (v 1.0.0.rc2), so I created a helper method that tries to use grouping first and then if the exception occurs it just retries without grouping, making the content span more than one page.
def group_if_possible(pdf, &block)
begin
pdf.group { block.call }
rescue Prawn::Errors::CannotGroup
block.call
end
end
Example: Using it when creating a table:
group_if_possible(pdf) do
pdf.table(rows)
end
EDIT:
Grouping were removed from Prawn 1.x but there is an unofficial grouping gem that works well for Prawn 2:
https://github.com/ddengler/prawn-grouping

Answer 2

Looks like Brad Ediger answered your question on Google Groups, but for the benefit of anyone else looking for help with this, here's his response:
Sadly, transactions do not yet work correctly when they start new
pages or change the pages collection. It's a known issue:
https://github.com/prawnpdf/prawn/issues/268
-be