# \*Lazy\* loading attributes

**URL:** <https://www.ruby-forum.com/t/lazy-loading-attributes/77535>\
**Category:** Rails\
**Created:** [November 28, 2006, 6:03pm UTC](https://www.ruby-forum.com/t/lazy-loading-attributes/77535 "2006-11-28T18:03:45Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![jonlog](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/db5fbb/32.png) [@jonlog](https://www.ruby-forum.com/u/jonlog)\
**Post date:** [November 28, 2006, 6:03pm UTC](https://www.ruby-forum.com/t/lazy-loading-attributes/77535/1 "2006-11-28T18:03:45Z")

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Imagine that I have a class Book, and a class Chapter, and Chapter has a  
text attribute that contains the text of the chapter. Is there a  
convenient railsy way to tell Chapter to only load chapter.text from the  
db when/if it’s specifically called for? For instance, if I’m using  
@book.chapters to build a TOC, I’m not the least bit interested in the  
chapter.text for all those chapters at this point, and am worried that  
loading all that extra data will slow down the app. I’m wondering if I  
can say something like…

class Chapter \< ActiveRecord::Base  
lazy\_load :text

or maybe…

class Book \< ActiveRecord::Base  
has\_many :chapters, :lazy\_load =\> [:text]

But so far the only option I can think of is to offload the text to it’s  
own model ChapterText that belongs\_to :chapter. I’ve been digging  
through the API off and on for a couple weeks now hoping to stumble on  
an elegant solution, but haven’t yet. So, I’m thinking it’s not  
currently possible, except for using an extra model. Ideas?

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**Author:** ![jonlog](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/db5fbb/32.png) [@jonlog](https://www.ruby-forum.com/u/jonlog)\
**Post date:** [November 28, 2006, 6:17pm UTC](https://www.ruby-forum.com/t/lazy-loading-attributes/77535/2 "2006-11-28T18:17:47Z")

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Jon G. wrote:

> ```
> lazy_load :text
> 
> ```
> 
> an elegant solution, but haven’t yet. So, I’m thinking it’s not  
> currently possible, except for using an extra model. Ideas?

I think the :select option for a find allows you to specify which  
columns to return. Something like…

Chapter.find(:all, :select=\>‘id, title’) will return Chapter objects  
with only the ‘id’ and ‘title’ populated.

Seems like it wouldn’t be too difficult to setup a class method that  
returns the names of all the columns without the ones you want to lazy  
load. You could then override the find method to automatically  
populate the ‘select’ option with these values.

Sounds like a good plugin exercise to me…

\_Kevin

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<div class="post-metadata">

**Author:** ![jonlog](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/db5fbb/32.png) [@jonlog](https://www.ruby-forum.com/u/jonlog)\
**Post date:** [November 28, 2006, 6:45pm UTC](https://www.ruby-forum.com/t/lazy-loading-attributes/77535/3 "2006-11-28T18:45:51Z")

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\_Kevin wrote:

> Sounds like a good plugin exercise to me…
> 
> \_Kevin

The problem there though, is that if you later try to access that data  
you didn’t load, ActiveRecord raises a “NoMethodError”, rather than  
going back to the database to get the data. I suppose if used very  
carefully though, that could be a viable option.

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<div class="post-metadata">

**Author:** ![jonlog](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/db5fbb/32.png) [@jonlog](https://www.ruby-forum.com/u/jonlog)\
**Post date:** [November 29, 2006, 1:17am UTC](https://www.ruby-forum.com/t/lazy-loading-attributes/77535/4 "2006-11-29T01:17:20Z")

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Jon G. wrote:

> > populate the ‘select’ option with these values.
> > 
> > Sounds like a good plugin exercise to me…
> > 
> > \_Kevin
> 
> The problem there though, is that if you later try to access that data  
> you didn’t load, ActiveRecord raises a “NoMethodError”, rather than  
> going back to the database to get the data. I suppose if used very  
> carefully though, that could be a viable option.

You might be able to use ‘method\_missing’ to load the ‘missing’ data  
when you need it.

\_Kevin