Railscasts - Rails 2.3 Extras

#152

Mar 09, 2009

29 comments

Rails 2.3 Extras

This episode finishes up this series on Rails 2.3. Here you will learn about several smaller additions in 2.3.

Tags: rails-2.3 active-record active-support

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gem install rails --source http://gems.rubyonrails.org

# find in batches
Product.count
Product.find_in_batches(:batch_size => 10) do |batch|
  puts "Products in batch: #{batch.size}"
end
Product.each(:batch_size => 10) do |product|
  puts product.name
end

# scoped_by
Product.scoped_by_price(4.99).size
Product.scoped_by_price(4.99).first
Product.scoped_by_price(4.99).scoped_by_category_id(3).first

# try method
Product.find_by_price(4.99).name
Product.find_by_price(4.95).name
Product.find_by_price(4.95).try(:name)
Product.find_by_price(4.99).try(:name)

# product.rb
default_scope :order => "name"

# categories_controller.rb
render 'new'
render 'products/edit'

<!-- products/index.html.erb -->
<%= render @products %>

<!-- products/show.html.erb -->
<%= render @product %>

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29 comments

1. Ubercow Mar 09, 2009 at 00:46

Very nice, I love the new 2.3 features

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2. Carl Mar 09, 2009 at 00:52

Those are some great features. I read a discussion somewhere that if you are using MySQL there can be a performance problem with the way the find in batches works with really large datasets (hundreds of thousands plus).

Many of these are features I can really see some great uses for in my projects already.

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3. Tex Mar 09, 2009 at 00:58

Great screencast as always !

Thanks Ryan !

I would like to see a screencast on i18n crud using globalize2 and Rails 2.3 nested form: is it possible ?

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4. Boblin Mar 09, 2009 at 01:43

I am waiting for nested models screencast too :)

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5. David Pierron Mar 09, 2009 at 02:41

Seems getting this RC2 from the listed source is returning RC1 for me. Is there a cache (DNS or something) that needs clearing to enable this new version for install?

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6. Markus Mar 09, 2009 at 04:07

Nice screencast. I'm on edge, but I did't realize that scoped_by_xxx was added (I still have to read the 2.3 release notes), it will clean once for all these one-purpose named scopes in model declaration.

One thing I noted while viewing your screencast is a important "detail" of the method .try I think you din't mention. .try changed from previous releases (I think it was already changed in RC1). Now only returns nil if you try(:something) over Nil, if you try(:something) over any other object, and :something it's not a method of that object, it will raise a NoMethodError. It's an important change to note, so it could lead to odd errors and to a misconception of the method purpose.

Thanks for all your awesome screencasts.

Cheers

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7. pimphamster Mar 09, 2009 at 09:39

Safari can’t open the page “http://media.railscasts.com/videos/152_rails_2_3_extras.mov” because it can’t find the server “media.railscasts.com”

I'm guessing there is just lots of traffic today

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8. Roger Mar 09, 2009 at 11:00

Thanks for railscasts!! What is the difference between scoped_by and find_by?

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9. Stephen Celis Mar 09, 2009 at 11:44

@Roger, you should check out the named_scope Railscast in the show notes. It should answer your question nicely.

The scoped_by method is just a dynamic way to return scopes, whereas find_by and find_all_by query the database and cannot be scoped any further.

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10. Stephen Celis Mar 09, 2009 at 11:45

P.S. Nice overview, Ryan! These are the cream of the crop!

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11. Allan Mar 09, 2009 at 16:42

Great screencasts.

How can I watch the video from Linux (Ubuntu) ?

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12. George Yacoub Mar 09, 2009 at 18:55

Thanks for the screencast Ryan.
+1 for globalize2 and Rails 2.3

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13. Jose Mar 10, 2009 at 12:18

Thanks for a great series, again

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14. Carl Mar 10, 2009 at 19:32

@Allan,

I use mplayer to watch the screencasts on Ubuntu. You can find some info here http://www.medibuntu.org/ about codecs that are sometimes needed to play some videos on Linux.

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15. Allan Mar 11, 2009 at 13:24

@Carl,

Thanks a lot. I'll look for it.

@Ryan,

I love your website design. Simple, pretty and effective. Thanks for all the greats screencasts. It's very useful for me.

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16. mk Mar 13, 2009 at 09:58

Hi Ryan,
I must say I really enjoy watching your screencasts and have benefited a lot from them, and I'd like to thank you for taking out time to do them. It can't be easy!

I have one request if you are able: would you be able to do a screencast on receiving email from a rails app?

Thanks and regards.
BTW What is the email that I can get to you on? [Please mail me] :)

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17. Andrew Vit Mar 15, 2009 at 13:25

Important: named_scope currently doesn't merge :order options. Hence, neither does default_scope...

The result is that if you set default_scope :order => "name" you will not be able to order by anything else in another scope, even if you specify a different order explicitly:

Product.by_price
Product.this_month :order => 'price'
# still ordered by name!

The only way to change the order is by setting it in the final find call, not a scope:

Product.all :order => 'price'
Product.this_month.all :order => 'price'

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18. Ozgur Mar 16, 2009 at 00:34

1)
I guess a nice use of default_scope would be while implementing "single table inheritance" structures.

I always had problems with the way rails handle it, but this way it is done behind the scenes. Perfect!

2)
In addition, I must say that I hated the way find_by_batches works. Splitting the badges according to a condition on id's is a bad idea. What if some records are deleted? Than batch sizes won't be predetermined. I would suggest the use of "LIMIT x, 10" syntax for a batch of size 10.
By the way this is true for MySQL, I don't know about the other DBMSs.

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19. justin Perkins Mar 17, 2009 at 17:23

This is for Rails 2.3.2 correct? I've got it running here and can't get the batch methods to work, instead I'm getting an undefined method exception when calling ModelName#each.

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20. Bill Burcham Mar 19, 2009 at 11:42

Yeah, I'd like to echo what Ozgur said. Without much analysis it seems to me that depending on object id's filling up the space from 1 up seems like a needless dependency on Rails implementation choices. AR#find already has support for :offset and :limit. Those seem preferable. Here's a class I find useful:

class Incrementally

 # Don't process every object in the database -- do it a few at a time
 def self.process( an_active_record_class, at_a_time = 1000)
 objects_count = an_active_record_class.count
 i = 0
 raise "at_a_time must be greater than 0" if at_a_time < 1
 until( i > objects_count)
 objects = an_active_record_class.find( :all, :offset => i, :limit => at_a_time)
 objects.each do |instance|
 if block_given?
 yield instance
 end
 end
 i += at_a_time
 end
 end
end # class

It could be made a lot nicer of course but you get the idea.

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21. mikhailov Apr 02, 2009 at 09:01

Excellent screencast!
As I see, the main goal batches process is get the number of objects from model like will_paginate.
Is it right?

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22. Marco Apr 10, 2009 at 07:34

Thanks Ryan,

A globalize2 screencast would be Great!

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23. Georg Ledermann Aug 17, 2009 at 03:16

Beware that .each has been renamed to .find_each after the screencast was published

http://github.com/rails/rails/commit/04333482bd665e4d4ced167ff4f566ecfc0cc919

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