Unixmonkey.net

I’m in the process of upgrading a Rails app from 2 to 3, and this proved to be a stumbling block.

Creating a message of any kind would result in a message like this:

NoMethodError: undefined method `new' for "smtp":String
from gems/mail-2.2.15/lib/mail/message.rb:252:in `delivery_method'
from gems/actionmailer-3.0.0/lib/action_mailer/delivery_methods.rb:74:in `wrap_delivery_behavior'
from gems/actionmailer-3.0.0/lib/action_mailer/delivery_methods.rb:83:in `wrap_delivery_behavior!'
from gems/actionmailer-3.0.0/lib/action_mailer/base.rb:641:in `mail'
from app/mailers/developer_mailer.rb:22:in `email_error_message'

This behavior comes from a method named lookup_delivery_method in the Mail gem.
The problem is that this method assumes the ActionMailer::Base.delivery_method to return a symbol like :smtp instead of a string like “smtp”. The old behavior worked fine in Rails 2.x apps.

I have different mailer settings per environment and load the settings in pretty much the same way Redmine does, by looping over a yml config file and using send to set actionmailer settings. The solution is to make sure it is created as a symbol like so:

# Loads ActionMailer settings from config/email.yml
# and turns deliveries on only if configuration block is found
config_file = Rails.root.join('config','email.yml')
 
if File.file?(config_file)
  mailconfig = YAML::load_file(config_file)
 
  if mailconfig.is_a?(Hash) && mailconfig.has_key?(Rails.env)
  # enable deliveries
  ActionMailer::Base.perform_deliveries = true
 
  mailconfig[Rails.env].each do |key, value|
    if value.respond_to?(:symbolize_keys!)
      value.symbolize_keys!
    elsif value.respond_to?(:to_sym)
      value = value.to_sym
    end
    ActionMailer::Base.send("#{key}=", value)
  end
else
  # disable deliveries
  ActionMailer::Base.perform_deliveries = false
end

Did you know that Excel can open a plain-old HTML table file and treat it just like a native Microsoft XLS file?

I’ve been doing this for ages, and its quite simple to pull off; just name your file something.xls and send the html with the content-type of “application/vnd.ms-excel” (and even that is not strictly required).

Even functions are somewhat supported like so.

<table>
  <tr>
    <td>2</td>
    <td>3</td>
    <td>=sum(a1:b1)</td>
  </tr>
</table>

However, there are a few drawbacks to this worth sharing when trying to style the tables with CSS.

1) Multiple class names are not supported:

<style type='text/css'>
  td.foo { background-color: red; }
</style>
<td class='foo bar'></td>

Will not apply the background color. You have to use only a single class per element like so:

<style type='text/css'>
  td.foo { background-color: red; }
</style>
<td class='foo'></td>

2) Descendant selectors are not supported:

<style type='text/css'>
  tr.odd td { background-color: red; }
</style>
<tr class='odd'>
  <td></td>
</tr>

Will not apply the background color either. You will have to be very specific about the element you want to style.

3) Certain colors and properties don't work:
If you use a color like #ECECEC (a light gray), it will come out white, If you use #CCCCCC (a darker gray) it will work. Stick to the basics like #000000 (black) if you can.

4) You'll have to add your styles either inline or in an html <style> block.
This shouldn't come as a surprise, but linking to an external stylesheet won't work. Excel won't reach out to your server to style the content.

5) Granularity will not be easily achieved:
Styling something with a 1px border is going to translate into a .5pt border. That's just how Excel rolls I guess.

Try marking up an Excel workbook and using 'save as' -> 'html' and opening up the file to checkout the markup Excel uses. This can give you some clues to what is acceptable.

I hope these simple tips help someone in a similar situation, and keep them from using a heavy arcane library to generate excel files with some added styling.

I’ve been crawling over this Rails project and lately finding lots of places where clarity could be increased by using symbol_to_proc, so I thought I would share it a bit for those not in the know on this handy ruby shortcut.

Rails added symbol_to_proc shorthand in version 1.1, and it is such a nice shortcut, that it became part of the Ruby language in version 1.8.7

So, anywhere you would normally use an iterator with a block like so:

people.collect { |p| p.name }

could be shortened to call like:

people.collect(&:name)

The difference may not look so dramatic in the above example, but how about this one:

   # classic
   prison.inmates.select{ |i| i.repeat_offender? }.select{ |i| i.offsenses }.collect{ |o| o.prosecution_fees }.sum

   # to_proc
   prison.inmates.select(&:repeat_offender?).select(&:offenses).collect(&:prosecution_fees).sum

Some people, including Rails core member pratik (http://m.onkey.org/2007/6/30/let-s-start-with-wtf)
Have criticized and advised against using this shortcut because it is roughly 4 times slower than doing without its syntax sugar.

Now, I would rather have a beautiful, understandable code base than a particularly fast one (after all, I *am* using Ruby), but the reason for the slowness is largely because of the implementation as shown below:

  class Symbol
    def to_proc
      Proc.new { |*args| args.shift.__send__(self, *args)
    end
  end

This implementation looks for arguments passed in and shifts self off of them before calling.
This allows for calling a method with arguments like so:

[1,2,3].inject(&:+)

I believe this represents a real edge case at the expense of a lot of speed, and Luke Redpath (http://lukeredpath.co.uk/blog/optimising-symbol-to_proc.html) has a lot of good to say about the topic, and even goes as far to present a patch for how this should be implemented for pure speed:

  class Symbol
  def to_proc
    @to_proc_proc ||= Proc.new { |obj| obj.__send__(self) }
  end
end

I’ve patched this in to my Rails project and not a single one of my tests failed, your mileage may vary, but even without the speed boost, I’ll continue to use :symbol.to_proc because I love it so.

I ran into an interesting issue today where a client viewing my Rails site would go to a link; and instead of seeing the html view rendered, it was skipping right to an alternate format in the respond_to block.

Clicking a link going to /orders, was instead taking them to /orders.xls, which I have in a respond_to block like so:

  def orders
    @orders = Order.all
    respond_to do |format|
      format.html # new.html.erb
      format.xls   # new.xls.erb
    end
  end

The client in question was using Internet Explorer. This provided a major clue.
It turns out that IE will send an HTTP_ACCEPT header listing all the stuff it can accept in the browser, and thus, because it can accept .xls files, it requests that format.

I’m experiencing this in a Rails 2.3.8 app, but documentation at railsguides.info states this behavior was changed in Rails 2.2. Perhaps an older plugin is switching it back on, I’ll have to investigate.

In any case, adding this line to application.rb solves the problem:

config.action_controller.use_accept_header = false

This causes it to behave as expected, where it uses the file extension alone to determine the format when there is a question which format to use.

For some complex searches, I find myself needing to build a query with some optional conditions that may or may not exist based on search terms.

I could concatenate an SQL string, but when we are dealing with user-supplied input, we need to parameterize the sql query with question marks (?) for binding parameters to to avoid SQL injection attacks.

But I may not know how many parameters I’m actually going to use in a query.

With a form like this:

Show me my friends: 
  living in: [   ]
  whose hobby is: () skating, () fishing, () basketball
  over: [  ] years old

  *(no required fields)

At first stab, you could try something like this:

User.friends.find(:all, :conditions => [
   'town LIKE ? AND hobby = ? AND age >= ?', 
   "%#{params[:town]}%", params[:hobby], params[:age] 
])

This would work, but only if all fields are filled out; otherwise the SQL generated would break looking like this if someone only filled in the name part of the form:

"SELECT * FROM users WHERE town LIKE "%indianapolis%" AND hobby = '' AND age >= ''"

There are some plugins like Ezra’s Ez-Where to handle query building; but how about we try using the built-in symbol key interpolation as described here in ActiveRecord to get the job done.

This lets you use named :symbols in place of question marks for binding.

Find lets you supply your conditions as a 2-element array with a string, and a corresponding hash like so:

User.friends.find(:all, :conditions => [ 
  'town LIKE :town AND hobby = :hobby AND age >= :age', 
  { :town => "%#{params[:town]}%" , :hobby => params[:hobby],  :age = params[:age] }
])

Again, this will work just fine if all fields are filled out; but how do we omit conditions and hash keys?

Our final SQL string can be built by joining conditions with AND (or OR if your app suggests it), and stuffing new key/value pairs into our arguments hash, or with Hash.merge!

First we’ll set up our search method like so:

def results
  conditions  = []
  arguments = {}
 
  unless params[:town].blank?
    conditions << 'town LIKE :town'
    arguments[:town] = "%#{params[:town]}%"
  end
 
  unless params[:hobby].blank?
    conditions << 'hobby = :hobby'
    arguments[:hobby] = params[:hobby]
  end
 
  unless params[:age].blank?
    conditions << 'age >= :age'
    arguments[:age] = params[:age]
  end
 
  all_conditions = conditions.join(' AND ')
 
  @user_friends = User.friends.find(:all, :conditions => [all_conditions, arguments])
end

An alternative is to use Hash.merge! like so:
(this will let you assign more than one key/value pair at a time or to combine hashes)

instead of:

arguments[:town]  = "%#{params[:town]}%"
arguments[:hobby] = params[:hobby]

  arguments.merge!({ 
    :town  => "%#{params[:town]}%",
    :hobby => params[:hobby]
  })

Maybe not as elegant as using a plugin, but certainly clear and flexible.

I’ve been playing around with Shoes (shoooes.net) lately as a way to put a cross-platform graphical user interface (GUI) on some of my small purpose-built command-line ruby scripts.

I find that it is quite easy to get started with, and lends a lot of flexibility to the way your program is structured and displayed. However, the structure feels a little bit alien compared to everyday ruby, and there are some gotcha’s you need to keep in mind while developing for Shoes.

I feel I must preface this article by saying that Shoes has excellent documentation, _why (the lucky stiff) turns documentation into its own art form. The manual, “Nobody Knows Shoes” reads a lot like a comic book, full of _why’s own original artwork and clippings from old-timey photos and art, and is complimented by the documentation at help.shoooes.net

I had a bit of trouble at first getting ActiveRecord to interface with a database from a straight port from one of my console apps because I glossed over the parts of the manual that detail the tricky behavior of the garbage collector reaping predefined classes after the app’s initial load.

The fix is pretty simple. Stick all your classes in an external file (or many) and load them using ‘require’.

Anyhow, here is a barebones example of a working implementation for using ActiveRecord in Shoes:

# in foo.rb
class Foo < ActiveRecord::Base
end
 
#in app.rb
Shoes.setup do
  gem 'activerecord'
  require 'active_record'
  ActiveRecord::Base.establish_connection(
    :adapter   => 'sqlite3',
    :dbfile    => 'foos_db.sqlite3'
  )
  require 'foo'
end
Shoes.app do
  @foos = Foo.find(:all)
  para @foos
end

Now, this example requires there is an existing sqlite database with a foos table, change out the establish_connection parameters to connect to any other database. The gem ‘activerecord’ statment tells shoes to install the activerecord gem into the shoes ruby library if it isn’t already there.

If you don’t already have a database, and just want to use a db to act as a storage layer for your app, then you might want to use ActiveRecord::Schema.define to create a database and setup the tables the same way you do for Rails migrations.

Here is a more complete example of an app to keep track of notes using ActiveRecord as the backend. I like the “base class that inherits from Shoes” pattern, so I’m using that here.

# in note.rb
class Note < ActiveRecord::Base
end
 
# in app.rb
Shoes.setup do
  gem 'activerecord' # install AR if not found
 
  require 'active_record'
  require 'fileutils'
 
  ActiveRecord::Base.establish_connection(
    :adapter   => 'sqlite3',
    :dbfile    => 'shoes_app.sqlite3'
  )
 
  # create the db if not found
  unless File.exist?("shoes_app.sqlite3")
    ActiveRecord::Schema.define do
      create_table :notes do |t|
        t.column :message, :string
      end
    end
  end
 
end
 
class ShoesApp < Shoes
  require 'note'
 
  url '/', :index
 
  def index
    para 'Say something...'
    flow do
      @note = edit_line
      button 'OK' do
        Note.new(:message => @note.text).save
        @note.text = ''
        @result.replace get_notes  
      end
    end
    @result = para get_notes
  end
 
  def get_notes
    messages = []
    notes = Note.find(:all, :select => 'message')
    notes.each do |foo|
      messages << foo.message
    end
    out = messages.join("n")
  end
 
end
 
Shoes.app :title => 'Notes', :width => 260, :height => 350

Here’s a screenshot:

There you are; a cross-platform desktop app that doesn’t require a full-on build environment, and can be distributed with the source exposed for later improvements.

The first time this runs, it installs Activerecord, requires it, establishes a connection, creates the table unless one already exists. Then it shows a form to add notes followed by all the existing notes in the database. Adding a new note refreshes the notes shown.

This isn’t exactly a polished app with full CRUD, but should prove a good introduction to Shoes for someone used to working with ActiveRecord.

I’ve got some data in an excel file that I need to put in the database and its far too much to do by hand, what will I do?

Lets throw some ruby at the problem!

First, excel it too darn complicated and proprietary a format to even mess with unless you are creating something really worth it, so lets open that .xls with Excel or OpenOffice and do a File -> Save As -> .csv (comma separated values) to get a file that is easier to work with.

Now, we could write our own CSV parser since its such a simple format, but why futz with it when someone else has already put out a good library for that will likely be more error tolerant? Lets use FasterCSV, as its pretty well-known.

Install by issuing:

sudo gem install fastercsv

Now you can just fire up script/console of your Rails app and type in the below, or just put this in a database migration to slurp up all that good spreadsheet data.

The below assumes you have a ‘users’ table with fields name, address, and email that are also rows in your excel file. Adjust as necessary.

require 'fastercsv'
FasterCSV.foreach("#{RAILS_ROOT}/myfile.csv") do |row|
  record = User.new(
    :name    => row[0], # first column of csv file
    :address => row[1], # second column
    :email   => row[2]  # third
  )
  record.save
end

That’s pretty awesome; now how can I export that stuff in the database back out to Excel again?

Lets use Ruport, the Ruby report gem!

sudo gem install acts_as_reportable

Toss the require statement somewhere obvious (like environment.rb or above the model you want to export), and put ‘acts_as_reportable’ in your model declaration.

require 'ruport'
class User < ActiveRecord::Base
  acts_as_reportable
end

Now I can do this kind of stuff to export to a csv file (again with script/console, but a migration should work equally well):

content = User.report_table.as(:csv) # convert your model table to CSV

or

content = User.report_table_by_sql("SELECT name, address, email FROM users").as(:csv)

Then write that to a file like so:

file = File.open("#{RAILS_ROOT}/report.csv", "w") # open file
file.print(content) # print that csv content to the open file
file.close          # close the file

Open that CSV file with Excel and amaze the sales team, your boss, or whoever.

This is a narrow view of what we can do with FasterCSV and Ruport, but I’m sure you can see how you could build out a format.csv in a respond_to block in a Rails controller, or have a setter in your model that sucks in an uploaded CSV to create some records.

These are some pretty great libraries, and I’m very glad they were able to help me load, combine, query and output some data I’d been working with in a pinch.

I hope this post serves to help someone else in a similar situation.

Sure, I haven’t even turned it on in more than 5 years, and I certainly didn’t use it very much back then either. Its been sitting in the bottom of the storage closet doing no one any good, yet it pains me just a bit to let it go.

Not because I won’t ever be able to turn it on again, as it was pretty likely I never again would, but because just having it gave me a small sense of “Hey, I was there. In that short time where computing had been pushed into the living rooms before it was practical, before the internet as we know it existed, where operating the computer was only a few steps away from programming it.”

The Commodore 128 was a gift to me from a lawyer who also hadn’t used it in years, but used it as a high-end word processor, as the backspace keys on typewriters left a tell-tale sign that you had definitely erased something (and with a pocketknife, you could probably tell what).

It wasn’t my first Commodore, though. I got a secondhand Vic-20 when I was about 8. It came with a manual that was little more than a “How to program basic” with some sample code to write some simple games, and some atari-like cartridges with games like “space invaders”, and “adventure”. I was a big fan of the text-based games. I later ended up tearing it apart to check out its innards, and left it broken for too long that circuit boards and small parts went missing.

I remember getting in trouble for “hacking” in school the first time we were taken to the new computer lab equipped with early apple’s running basic, and I had instructed the computer to run an infinite loop of the below program I had learned from my trusty Commodore manual.

10 PRINT "TOMMY STINKS"
20 GOTO 10

I had a friend whose father was an avid computer geek in these mid-to-late 80’s days, who would pirate video games by tuning his ham-radio to a station that broadcast the analog signal he could tape onto a cassette he could read back into the computer.

I don’t know if I’m reminiscing, or just trying to hold on to the memory of the way things were because they were so drastically different from today. The information economy and the internet as we know it has forever changed the way we work, play, and live.

Anyhow, I’ll miss the Commodore all the same; but I’m happy it found a new home, freed up some of my closet space, and helped me put down the deposit on my new apartment.

I took a bunch of pictures before putting it up on eBay, you can see them all here: https://unixmonkey.net/Commodore/

The web is a generally free and open place for all types of communication, but if you put your email address on 1 website, you can expect an email-harvesting robot spider to find that address and send it to its spammer overlords.

Once on a spammer’s list, you can expect to get all kinds of interesting stock tips, products to enhance your manhood, and friendly letters from Nigerian diplomats.

If you simply have too little to do in the day, this can be a great way to meet new people and start a career in day trading. However, some of us are just too darn busy to stop what we are doing every 2/3rds of a second to check our email; but still need it for keeping in contact with friends, family, and business contacts.

From a few tips pulled from the web, I set to create a nice link helper for Ruby / Rails intended to display email links that work indistinguishably from regular mailto: links, and even gracefully downgrade for users without javascript.

Lets not even display the email address on the page at all, and use a little javascript to render the email address after the fact by breaking it up and putting it back together with javascript.

# Takes in an email address and (optionally) anchor text,
# its purpose is to obfuscate email addresses so spiders and
# spammers can't harvest them.
def js_antispam_email_link(email, linktext=email)
    user, domain = email.split('@')
    # if linktext wasn't specified, throw email address builder into js document.write statement
    linktext = "'+'#{user}'+'@'+'#{domain}'+'" if linktext == email 
    out =  "<noscript>#{linktext} #{user}(at)#{domain}</noscript>n"
    out += "<script language='javascript'>n"
    out += "  <!--n"
    out += "    string = '#{user}'+'@'+'#{domain}';n"
    out += "    document.write('<a href='+'ma'+'il'+'to:'+ string +'>#{linktext}</a>'); n"
    out += "  //-->n"
    out += "</script>n"
    return out
end

This is probably good enough for 90% of those robots, but you know if one spammer gets your address, he will likely share (or sell) your email to all his friends. The weak spot in this looks like the noscript version, lets fuzz that up a bit by converting to HTML character entities.

One of the earliest and simplest ways to obfuscate an email address is by converting each character into its HTML equivalent. This makes the source look nasty, but will be correctly rendered by the browser that the end-user is none the wiser.

An address like abc@example.com will look like this in the source:

abc@example.com

Let’s build a simple method to convert a plaintext string into something like the above. I’m going to cheat and only convert a-z and A-Z and leave @ signs, dots, dashes, etc. alone.

# HTML encodes ASCII chars a-z, useful for obfuscating
# an email address from spiders and spammers
def html_obfuscate(string)
  output_array = []
  lower = %w(a b c d e f g h i j k l m n o p q r s t u v w x y z)
  upper = %w(A B C D E F G H I J K L M N O P Q R S T U V W X Y Z)
  char_array = string.split('')
  char_array.each do |char|  
    output = lower.index(char) + 97 if lower.include?(char)
    output = upper.index(char) + 65 if upper.include?(char)
    if output
      output_array << "&##{output};"
    else 
      output_array << char
    end
  end
  return output_array.join
end

now in our js_antispam_email_link method we can “encrypt” the user and domain before sending to the browser like so:

def js_antispam_email_link(email, linktext=email)
  user, domain = email.split('@')
  user = html_obfuscate(user)
  domain = html_obfuscate(domain)
  ...

Not bad, but many spiders these days can still decode HTML entities and get at that address, so lets build up our defenses a bit more by adding some methods to really screw with those spiders.

We’ll write a method that encrypts a string with ROT13 and puts that on the webpage, and use some javascript to decrypt that on page display. ROT13 is a really simple cipher where you take characters a-z and shift them by half the alphabet.

This is a really simple one-liner borrowed from Jay Komineck

# Rot13 encodes a string
def rot13(string)
  string.tr "A-Za-z", "N-ZA-Mn-za-m"
end

Lets use this to really beef up our link helper by using some javascript that can decipher this. JS code taken from Allan Odgaard

string = '#{email}'.replace(/[a-zA-Z]/g, 
  function(c){ 
    return String.fromCharCode(
      (c <= 'Z' ? 90 : 122) >= (c = c.charCodeAt(0) + 13) ? c : c - 26
    );
  });

Now we’ve got some pretty strong defense against those pesky robots and by using simple HTML character encoding and lightweight ROT13 ciphering it shouldn’t be too taxing on your webserver to spit out a page with a few emails on it. Less sophisticated browsers still get the contact info and everyone is a little bit happier to come home to a (relatively) clean inbox.

Here’s the whole shebang put together, put this in application_helper.rb if using rails:

# Rot13 encodes a string
def rot13(string)
  string.tr "A-Za-z", "N-ZA-Mn-za-m"
end
 
# HTML encodes ASCII chars a-z, useful for obfuscating
# an email address from spiders and spammers
def html_obfuscate(string)
  output_array = []
  lower = %w(a b c d e f g h i j k l m n o p q r s t u v w x y z)
  upper = %w(A B C D E F G H I J K L M N O P Q R S T U V W X Y Z)
  char_array = string.split('')
  char_array.each do |char|  
    output = lower.index(char) + 97 if lower.include?(char)
    output = upper.index(char) + 65 if upper.include?(char)
    if output
      output_array << "&##{output};"
    else 
      output_array << char
    end
  end
  return output_array.join
end
 
# Takes in an email address and (optionally) anchor text,
# its purpose is to obfuscate email addresses so spiders and
# spammers can't harvest them.
def js_antispam_email_link(email, linktext=email)
  user, domain = email.split('@')
  user   = html_obfuscate(user)
  domain = html_obfuscate(domain)
  # if linktext wasn't specified, throw encoded email address builder into js document.write statement
  linktext = "'+'#{user}'+'@'+'#{domain}'+'" if linktext == email 
  rot13_encoded_email = rot13(email) # obfuscate email address as rot13
  out =  "<noscript>#{linktext}<br/><small>#{user}(at)#{domain}</small></noscript>n" # js disabled browsers see this
  out += "<script language='javascript'>n"
  out += "  <!--n"
  out += "    string = '#{rot13_encoded_email}'.replace(/[a-zA-Z]/g, function(c){ return String.fromCharCode((c <= 'Z' ? 90 : 122) >= (c = c.charCodeAt(0) + 13) ? c : c - 26);});n"
  out += "    document.write('<a href='+'ma'+'il'+'to:'+ string +'>#{linktext}</a>'); n"
  out += "  //-->n"
  out += "</script>n"
  return out
end

I hope this helps out somebody out there, please leave a comment if you have any suggestions.

If you’ve ever wanted to keep track of revisions to document files or images in your Rails app, you are likely to want to use Acts_as_versioned, which is the authority on versioning database records, and Attachment_fu, which is the authority on uploading files with Rails.

The problem is that they don’t know about each other and will step on each other’s toes without some changes. This article serves as a quick introduction to each, and shows how to make the two plugins get along like best friends.

Acts_as_versioned was written by Rails Core Team member Rick Olsen (who also wrote attachment_fu and Restful_authentication among others) that essentially makes a mirror table of the one you want to version, and keeps every version of the record you are updating.

Say I have a document table with fields like this:

Acts_as_versioned will add a column “version”, and a separate table “document_versions”.

The document_versions table will look a bit like this

Setting up acts_as_versioned is pretty simple, I got most of my introduction to it from urbanhonking.com

Now every time you update the original document, the changes are saved in your main documents table, and the version column is incremented by 1.

After a few edits of the document, you’ll see the versioning information in the Document_versions table add up.

Great! We can now use some of acts_as_versioned’s built-in methods for determining if there are older versions, and be able to view or even revert to them.

Now lets add the ability to upload a file to attach to a document record with attachment_fu.

Attachment_fu is another plugin that makes uploading files and keeping track of them in the database relatively simple.

A good intro to attachment_fu can be found on Mike Clark’s blog

Attachment_fu would require a few changes to our documents table:

Don’t forget to add the same fields to your documents_versions table, too.

Once we’ve added the right file fields to the new and edit forms, and image_tag or download link on the show view, we’ve got working file uploads. Nice.

Try to edit a record by attaching a new file, the new file is displayed and the record is preserved as an older version in the versioned table. But if you try to view the old version…wait a minute? Where did my version 1 file go!

That’s right, attachment_fu deletes the old file when you add a new one (as it should if you aren’t versioning your data). Attachment_fu’s rename_file method is the one responsible for deleting (or renaming) the old file when a new one is added, so lets monkeypatch that in our model to not do anything.

def rename_file
end

Now, it will only overwrite the file if the filename is the same. Lets store each version in its own folder to keep them from clobbering each other by monkey-patching the path files get written to in our model also:

def attachment_path_id
  "/#{id}/v#{version}/"
end
def partitioned_path(*args)
  attachment_path_id + args.to_s
end

This changes the public path from /0000/0001/rep08.jpg to /1/v1/rep08.jpg

Now, if we want to display the image, we cannot use the ‘public_filename’ method, because it is only given to the Document model, and not the Document_Version model.

That’s okay, because with our new path arrangement, we can reliably predict where the old versions of the files will be kept. You can show them with some code similar to this in your views:

<% for version in @document.versions %>
 
  Version <%= version.version %>
  <%= image_tag("/documents/#{@document.id}/v#{version.version/" + version.filename) %>
  <hr />
 
<% end %>

Now, when we delete a record, attachment_fu only knows about the current document, and will leave behind orphaned files and folders from the old versions. Lets fix that by having it get rid of the document id folder.

Rails reserves some special methods (callbacks) for performing actions before or after other major actions, lets tap into that by defining a method that will magically get called every time we delete a record.

def after_destroy
  FileUtils.rm_rf(RAILS_ROOT + "/public/documents/#{id}/")
end

This translates into the shell command rm -rf and deletes our ID directory and everything inside it.

Hooray!

As a wrap up, lets look at our complete Document model:

class Document < ActiveRecord::Base
  acts_as_versioned
  has_attachment :storage => :file_system
 
  def rename_file
  end
 
  def attachment_path_id
    "/#{id}/v#{version}/"
  end
 
  def partitioned_path(*args)
    attachment_path_id + args.to_s
  end
 
  def after_destroy
    FileUtils.rm_rf(RAILS_ROOT + "/public/documents/#{id}/") if id
  end
 
end

I’ve whipped up a sample Rails app demonstrating the points and code in this article. It uses Rails 2.0.2 with the sqlite3 database.

Download it here: Attachments_versioned (240kb .zip)

I hope this saves some work for someone who wants to leverage these two excellent plugins by Rick Olsen (technoweenie) on the same model without having them fight too much.