Railscasts - Eager Loading

1. Jake Apr 23, 2007 at 00:29

I always get excited when I see the (1) next to railscast in my RSS reader. Another great tip!

2. skycn Apr 23, 2007 at 00:31

so good ,thank you .
love it!

3. sintaxi Apr 23, 2007 at 00:40

I often refer back to these casts while I work. Thank you.

4. riki Apr 23, 2007 at 01:40

Thank you! These are great.

5. Rutra Apr 23, 2007 at 01:47

You are doing fantastic job, Thank you!

6. dima Apr 23, 2007 at 02:40

Thank you for your astonishing effort.
You give us a great educational place.

To all my new rails colleagues I recommend your screen casts as an easy to understand knowledge mine.

7. Ted Apr 23, 2007 at 06:17

Great stuff as usual.

I'd like to have seen the before and after results of including comment and user counts on the task list and how the database queries were affected when you added them to the find include.

8. Kevin Apr 23, 2007 at 06:20

Just to echo the praise above, thank you! I too look forward to seeing an update in my RSS reader; keep up the great work.

9. Ryan Bates Apr 23, 2007 at 07:47

Thanks everyone for the encouraging comments.

@Ted: I think you'll only see a boost in performance if you're displaying the comment and user name for each task in the list. Each task will need an additional query to fetch the comments, and each comment would need another query to fetch the user name. If you're displaying a significant number of tasks with comments then this can get out of control. Eager loading will reduce this all to one big query with lots of joins.

That said, if you're just displaying the number of comments and not the entire comment content, you won't see much of a boost in performance with eager loading because it will be fetching more information from the database (the content of the comment) and not just the number of comments. I cover this problem in the next episode.

10. Pablo Apr 23, 2007 at 07:55

Excelete trabajo, disfruto mucho viendo estos railcast y espero muy entusiasmado cada vez que hay uno nuevo.
Felicitaciones !!!

Excelent Work, I enjoy a lot seeing those railscast, Im awaiting very enthusiastic each time that there is a new one.
Congratulation !!!

11. Chris G Apr 23, 2007 at 08:39

Again, very helpful!

Railscasts has recently become my favourite TV show, im not kidding! Awesome job Ryan!

12. Hugh Apr 23, 2007 at 09:47

Nice screencast.

Do you ever get name clashes with eager loading? IE, since a project and a task both have the column 'name', when using eager loading you might get a Invalid SQL exception.

13. Xilo32 Apr 23, 2007 at 10:01

Hey Ryan,

Thank you for putting out great screencasts. Great work. Great quality. Awesome contribution to the community.

14. David Parker Apr 23, 2007 at 10:14

Ryan,

I really enjoy your screencasts. Keep up the great work!

15. Ryan Bates Apr 23, 2007 at 10:53

@Hugh,

Good point, I should have mentioned this in the screencast. You can avoid name clashes by specifying the table name in front of any mentioned column name. For example:

Topic.find(:all, :include => :project, :order => 'topics.name')

You can do the same in the conditions parameter and anywhere else.

Note to self: add some code formatting in comments.

16. Wandschrank Apr 23, 2007 at 13:40

You open my eyes. I am a better human now.

17. Luis Felipe Hurtado Apr 23, 2007 at 15:26

Como dice mi abuelita: "si vas a hacer algo, hazlo lo pero bien hecho". Este trabajo es excelente y de mucha calidad.

18. Daniel Steinsland Apr 23, 2007 at 16:27

I love Railscasts, it's a simple no fuzz approach to learning rails. I do wish I could watch the podcast on my Apple TV however. Just a thought. Keep up the good work!!!

19. Ryan Bates Apr 23, 2007 at 16:36

Railscasts are coming soon to an AppleTV or iPod near you.

20. Rebort Apr 23, 2007 at 16:52

Love the screencasts and the recent additions of the site.

Have you thought about doing screenshots or having sample code up next to each video?

The reason I ask -- I'm trying to remember something you did with a User model and the =|| operator, but I can't remember which video it was in!

Anyway -- thanks for sharing the knowledge and putting out a great site!

21. Ryan Bates Apr 23, 2007 at 16:58

@Rebort,

Great ideas, thanks. I'm trying not to add to the amount of work for each episode, but I'll give it some serious consideration.

The ||= operator is described in the very first episode on caching with instance variables.

22. Pepe Apr 24, 2007 at 00:04

Congratulations ;)
Ryan can you explain the link_to xxx, xxx_path(xxx)? I tried it and it didn't work.

23. Ryan Bates Apr 24, 2007 at 07:36

@Pepe, the "_path" method is called a named route. This is generated automatically when you are doing a RESTful design. I'll try to cover it in a future episode.

Great idea, thanks.

24. Shaliko Apr 24, 2007 at 08:26

Thank you!

Always great pleasure to studying your video. And always Malreaux them.

25. Jack Apr 24, 2007 at 16:54

Great cast as always!

26. Jack Apr 24, 2007 at 16:55

Have you ever considered getting more coders on board to contribute railcasts? I ask purely out of greed, I just can't get enough or RoR screencasts :)

27. RuMiL Apr 24, 2007 at 19:44

You rulez Ryan!
I love the railscasts, even when I don't speak english, I can understand and learn a lot more on every episode.

:)

28. Dougal Apr 24, 2007 at 21:32

Like many others, I get excited when ever my RSS reader shows there is a new screencast. Keep up the good work Ryan. Very helpful.

29. Ryan Apr 24, 2007 at 22:18

I enjoy the screencasts. Some of them I find to be a little too basic, but I often get something worthwhile out of them. I do, however, like the path you're taking--it seems like the topics are getting more and more in-depth.

As a future request, I would love to see a screencast or two on modules and mixins. I'm starting to get into meta-programming, but I find it really, really confusing in the beginning.

Keep up the good work!

30. J. Kyle Apr 24, 2007 at 23:43

Much thanks again and again and again, Ryan!

31. Warren Henning Apr 24, 2007 at 23:47

Just wanted to say that I appreciate you taking the time to make these screencasts.

Information delivered in little bite-sized chunks is often much more palatable than massive cram sessions.

32. Grant Neufeld Apr 25, 2007 at 05:31

Clear, concise, and very useful. Thanks for your excellent Railscasts.

What are you using to get the pretty-printed live display of your development.log in the Terminal?

What are you using to get command-key strokes displayed in that little popup near the top right?

Thanks!

33. Bryce Apr 25, 2007 at 08:20

Thanks for the great screencasts. It's like having another friend coding next to you. I've used a lot of your tips to clean up the code I'm working on and it's really helped out my development a ton.

Thanks,
Bryce

34. Ryan Bates Apr 25, 2007 at 08:25

@Jack, maybe someday I'll get more contributors to Railscasts, but at the moment I like to keep things simple and controllable.

@Ryan, an episode on modules and mixins is a great idea. I'll add it to my list. :)

@Grant, the live display of the development.log file is just coming from when I run "script/server", I guess mongrel is automatically set up to display this. If it's not displaying it for you, you can run this command (probably won't work on Windows)

tail -f log/development.log

The keystrokes are being displayed using KeyCastr.

http://stephendeken.net/software/keycastr/

Thanks for the encouraging comments folks!

35. Andy Apr 26, 2007 at 08:24

Simply wonderful. Your screencasts have become part of my rails learning toolkit, offering quick, clear and genuinely useful tips. Thanks.

36. Trueque Apr 27, 2007 at 02:04

Wonderful. This really better than any tutorial.

Thanks!!

37. Grant Neufeld Apr 27, 2007 at 08:09

Thanks for the answers. KeyCastr is a very good idea for screencasts.

I’ve been using Locomotive on Mac OS X for my Rails development, so I hadn’t been calling script/server directly. I had also just been opening my logs in Textmate or TextWrangler, so hadn’t realized there was pretty-printing that would pick up in tail.

Thanks again!

38. InMan Apr 27, 2007 at 10:19

I have code in helper:
  def page_methods(page)
    str = " "
    str += ( link_to blabla ) unless page.first?
    str += ( link_to blublu ) unless page.last?
    str
end

I found that first? and last? makes new query to database. How can i tell to use already made page query where i fetch all data.

39. Ryan Bates Apr 27, 2007 at 15:02

@InMan,

Are you using some form of pagination here? I can't tell why it is querying with just that code. I suggest starting a thread on http://railsforum.com instead of discussing it here. That way you can post more code. I'll try to respond there if I know the answer.

40. InMan Apr 28, 2007 at 04:07

I forgot to say that i am using plugins:
acts_as_tree
acts_as_list :scope => :parent_id

41. Horatio Apr 30, 2007 at 02:34

I'll say it again...this is awesome! I have been digging to find an example of this in practice for a while! More specifically the multiple levels of including. Great job!

42. supaspoida May 16, 2007 at 16:33

Just wanted to say that your Railscasts have been helping me tremendously while trying to learn rails. I've worked my way out of several tough spots to grasp using them, thanks!

I had one question about this episode though. I am working on a gallery type page for my portfolio, and I am using eager loading to call up categories, projects, and images all at once. I am wondering if there is a way to limit just one of the models returned? For example I only want to retrieve 5 projects per page. Where would I put the limit condition? This is what I have in my category model right now:

def self.portfolio
find_all_by_parent_id(2, :include => { :projects => :images }, :conditions => 'images.default = true' )
end

Thanks!

43. Ryan Bates May 17, 2007 at 10:27

Very good question. AFAIK the limit clause in SQL is very limiting, and I don't think it's possible to do this with an SQL LIMIT (find :limit parameter). See if fetching all of the projects gives you decent performance. If not you could try not fetching the projects and doing a separate SQL query for each category, fetching the limited projects. This is a good way to go if you don't have many category models.

If you want to do this all in one query, I'm sorry I don't know how. I'm sure it's possible with a custom SQL query, but I'm not proficient enough with SQL to know.

44. sfty Aug 24, 2007 at 14:18

now that rails edge has query caching, eager loading may not always be the optimal solution, esp. with :select not working, one has to pull every column of all the tables :include'd.

see technoweenies "trick":
http://activereload.net/2007/5/23/spend-less-time-in-the-database-and-more-time-outdoors
http://pastie.caboo.se/63741

me thinks it would be really cool to have a follow-up on this episode. :)

45. sfty Aug 24, 2007 at 14:57

in context with my previous post, here I have another nice link concerning the problems with eager loading:

http://darwinweb.net/article/Free_Form_Manual_Eager_Loading

46. Matt Aug 27, 2007 at 08:49

Great episode! For anyone using eager loading on large databases, to get a huge performance boost you should set the column to index on the database of the attribute you're including, e.g. setting the task_id column in the projects table to be an index column using the sql command
ALTER TABLE `projects` ADD INDEX ( `task_id` )

47. Oscar Del Ben Oct 17, 2007 at 08:32

Thanks

48. shruthi Nov 11, 2007 at 17:25

Thank you very much. Its been of great help

49. smacak Nov 19, 2007 at 13:32

One word for you. Amazing! Thanks for these great screencasts. Keep up the good work.

50. Captain Zhan Mar 19, 2008 at 08:20

Simple but nice. Thank you for it.

51. Avishai Mar 27, 2008 at 20:58

Excellent tutorial :-)

Is it possible to get one piece of related data with out actually making a model for it? For example, I have Places and Countries, but I don't need/want a Country model, so I did Place.find(:all, :joins => 'LEFT JOIN countries ON places.country_id = countries.id'). The query executes, but I can't figure out how to access the resulting country name. Does anyone know?

Thanks!

52. kino May 23, 2008 at 01:51

Thus, the Ideal of pure reason proves the validity of the architectonic of natural reason.

Eager Loading

52 comments

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