# Application Design

**URL:** <https://www.ruby-forum.com/t/application-design/95877>\
**Category:** Rails\
**Created:** [June 17, 2006, 4:20am UTC](https://www.ruby-forum.com/t/application-design/95877 "2006-06-17T04:20:43Z")\
**Posts on this page:** 9\
**Page:** 1

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**Author:** ![Laz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/ce73a5/32.png) [@Laz](https://www.ruby-forum.com/u/Laz)\
**Post date:** [June 17, 2006, 4:20am UTC](https://www.ruby-forum.com/t/application-design/95877/1 "2006-06-17T04:20:43Z")

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Hey,

I have a system that I am trying to design, it contains news articles,  
events, etc… There is model representing articles, one representing  
events, etc…

Articles or events can be active or inactive, so I can do a query to  
return all active articles, all articles or all inactive articles.

The question that I have is what would be the best way to design this.  
Right now I have each method (such as recent articles, featured  
articles, etc…) taking an ‘active’ parameter. This requires littering  
the code with method calls taking this parameter.

I have also thought about setting a class variable on the models to set  
whether active/inactive/all articles are returned, so that anytime you  
want to set the type returned you set this class variable and then call  
your functions (recent\_articles, etc…).

What I would like to know is if there are any suggestions as to a good  
practice to follow in how to implement this functionality, one of the  
ways I have stated or some other way that I haven’t considered.

I hope I have been clear. Thanks for the help in advance.

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<div class="post-metadata">

**Author:** ![Laz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/ce73a5/32.png) [@Laz](https://www.ruby-forum.com/u/Laz)\
**Post date:** [June 17, 2006, 6:30am UTC](https://www.ruby-forum.com/t/application-design/95877/2 "2006-06-17T06:30:58Z")

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Ditto, same question. Seems like there are 3 pretty obvious ways to do  
it…

But…

Is there a Ruby (e.g., elegant) Way to do this?

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<div class="post-metadata">

**Author:** ![Laz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/ce73a5/32.png) [@Laz](https://www.ruby-forum.com/u/Laz)\
**Post date:** [June 17, 2006, 9:36am UTC](https://www.ruby-forum.com/t/application-design/95877/3 "2006-06-17T09:36:03Z")

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On 6/16/06, Laz [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> The question that I have is what would be the best way to design this.  
> Right now I have each method (such as recent articles, featured  
> articles, etc…) taking an ‘active’ parameter. This requires littering  
> the code with method calls taking this parameter.

Use a method call with the ‘active’ parameter set to default  
def recent\_articles( since = 5.days.ago, is\_active = true )

that way when you call recent\_articles if you don’t specify a parameter  
it  
will use true and 5 days ago

I have also thought about setting a class variable on the models to set

> whether active/inactive/all articles are returned, so that anytime you  
> want to set the type returned you set this class variable and then call  
> your functions (recent\_articles, etc…).

This would be very bad when multiple requests are being served I think.  
Also you would still have to set the condition in each call to a method  
since you won’t know what state the class variable will be in. I would  
stay  
away from this one.

What I would like to know is if there are any suggestions as to a good

> practice to follow in how to implement this functionality, one of the  
> ways I have stated or some other way that I haven’t considered.
> 
> I hope I have been clear. Thanks for the help in advance.

–

> Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/).
> 
> * * *
> 
> Rails mailing list  
> removed\_email\_address@domain.invalid  
> [http://lists.rubyonrails.org/mailman/listinfo/rails](http://lists.rubyonrails.org/mailman/listinfo/rails)

I’m not 100% sure that I understand your problem but…

I’m assuming that something has recent articles, and active articles  
etc.  
I’ll assume it’s news ie news has\_many articles

So I think if you wanted to call news.articles and only return open ones  
To do this, in the News class

has\_many :articles, :conditions =\> { :active =\> true } # get only active  
articles with news.articles

has\_many :all\_articles, :class\_name =\> “Article” # get all articles  
associated with news with news.all\_articles

has\_many :inactive\_articles, :class\_name =\> “Article”, :conditions =\>  
{:active =\> false } #

has\_many :recent\_articles, :class\_name =\> “Article”, :conditions =\>  
“active  
= true AND published\_at \> #{5.days.ago}” # news.recent\_articles

I haven’t tested this so I’m not sure that it will do what you want but  
I  
think it should.

Alternatively you could make some class methods on your articles or  
instance  
methods on your News class etc

class Article \< ActiveRecord::Base

```
class << self
   def recent_articles
       find( :all, :conditions => "published_at > #{5.days.ago}" )
    end
end

```

…  
end

Call this via Article.recent\_articles

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<div class="post-metadata">

**Author:** ![Laz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/ce73a5/32.png) [@Laz](https://www.ruby-forum.com/u/Laz)\
**Post date:** [June 17, 2006, 9:47am UTC](https://www.ruby-forum.com/t/application-design/95877/4 "2006-06-17T09:47:14Z")

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Thanks Daniel,

Yea, the first examples you showed is the way I’m basically doing it  
now, except not using true or false, because I need 3 options (active,  
inactive, all).

Your second comment about having to keep track of the state of the  
object (i.e. whether it is in active/inactive/all state) was a point  
bothering me in that implementation, but I was wondering if the state  
monitoring would be offset by the fact that most of the time when these  
methods are called, it is within a small method itself, therefore just  
setting the state at the beginning of that method may not have been hard  
to keep track of. Any thoughts on this?

Your third suggestion looks interesting, I hadn’t thought of that, have  
to give that one some thought now.

Thanks for the reply. If you have any more thoughts on what I said or  
any others, don’t hesitate. I’m trying to broaden my programming skills  
by learning from best practices and getting good feedback. Thanks again  
Daniel.

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<div class="post-metadata">

**Author:** ![Laz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/ce73a5/32.png) [@Laz](https://www.ruby-forum.com/u/Laz)\
**Post date:** [June 17, 2006, 9:36am UTC](https://www.ruby-forum.com/t/application-design/95877/5 "2006-06-17T09:36:07Z")

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Is there a newsgroup more suited to this question that I should have  
posted it or is this one ok?

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<div class="post-metadata">

**Author:** ![Laz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/ce73a5/32.png) [@Laz](https://www.ruby-forum.com/u/Laz)\
**Post date:** [June 17, 2006, 10:15am UTC](https://www.ruby-forum.com/t/application-design/95877/6 "2006-06-17T10:15:31Z")

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On 6/17/06, Laz [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> monitoring would be offset by the fact that most of the time when these  
> methods are called, it is within a small method itself, therefore just  
> setting the state at the beginning of that method may not have been hard  
> to keep track of. Any thoughts on this?

Setting the state on an instanciated object is no problem. That status  
effects only that object. You could then put an instance method on it  
to  
query its state. But putting the state as a class variable will mean  
that  
if every instance of that object sets the class variable and you read a  
couple of hundred instances of article from your db you could be in all  
sorts of strife… especially if there is someone else reading those  
objects  
and changing their state at the same time. If you check the state in  
the  
method, then go to use it, it may have changed you just don’t know.  
Class  
variables are good for things like allowable states.  
@@states = [“active”,“inactive”, “something else”]

in you db table (and with rails therefore an instanciated object) for  
Articles you presumably have a column called status. You can determine  
what that status is set to by using

@my\_article.status

This will return the status of the article. You could also define an  
instance method that looks more like a question

def is\_active?  
self.status == “active”  
end

This will return true if the status of the article is set to “active”  
by a  
call to @my\_article.is\_active?

The things that you can do with this are very flexible.

Say you set up the is\_active? method above and you have a collection of  
Articles in a variable.  
say you used  
articles = Articles.find(:all )

You can split these into active and inactive by using  
active\_articles, inactive\_articles = articles.partition{ |a|  
a.is\_active? }  
Partition is a method of the Enumerable module.

Then you could select recent articles by  
recent = active\_articles.select{ |a| a.publised\_at \> 5.days.ago }

There are many ways to get the functionality that your after… Many  
more  
than I know about. Which one to use is probably the tricky part.

Do you use the has\_many option from the previous post. It may hit the  
db a  
few more times. But if you grab the Articles as above via a find(:all)  
and  
there are big articles and plenty of them, then your memory usage may be  
too  
much. You could alleviate that by

articles = Articles.find(:all, :limit =\> 100, :order =\> “published\_at  
DESC”  
)

either way, if this is going to be something that you do regularly it is  
best, I believe, to wrap it up into a method. This will keep the logic  
in  
one place, and if you need to change it you will know exaclty where to  
go.

Your third suggestion looks interesting, I hadn’t thought of that, have

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<div class="post-metadata">

**Author:** ![Laz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/ce73a5/32.png) [@Laz](https://www.ruby-forum.com/u/Laz)\
**Post date:** [June 17, 2006, 10:41am UTC](https://www.ruby-forum.com/t/application-design/95877/7 "2006-06-17T10:41:51Z")

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You are right Daniel, what I should have been saying was instance  
variable. It is a per-object reference that I was thinking about. My  
mistake. So in that case then, would you think that it might be better  
design to keep the active state stored as that instance variable,  
therefore avoiding passing it into all the method calls, or keeping it  
explicitly in the method calls?

Was there more to your comment as it seems to have been cut off, I think  
the forum may have gone down for a second.

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<div class="post-metadata">

**Author:** ![Laz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/ce73a5/32.png) [@Laz](https://www.ruby-forum.com/u/Laz)\
**Post date:** [June 17, 2006, 9:55pm UTC](https://www.ruby-forum.com/t/application-design/95877/8 "2006-06-17T21:55:55Z")

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Thanks for the help Daniel. Greatly appreciated. Maybe I can repay the  
favour one day.

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<div class="post-metadata">

**Author:** ![Laz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/ce73a5/32.png) [@Laz](https://www.ruby-forum.com/u/Laz)\
**Post date:** [June 17, 2006, 2:09pm UTC](https://www.ruby-forum.com/t/application-design/95877/9 "2006-06-17T14:09:04Z")

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On 6/17/06, Laz [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> You are right Daniel, what I should have been saying was instance  
> variable. It is a per-object reference that I was thinking about. My  
> mistake. So in that case then, would you think that it might be better  
> design to keep the active state stored as that instance variable,  
> therefore avoiding passing it into all the method calls, or keeping it  
> explicitly in the method calls?

In my opinion it is definitley good practice for an object to know it’s  
state. In theoretical OOP design, an object should not allow other  
objects  
access to it’s internal workings. It should provide a way for other  
objects  
to ask it what a property is set to, and also tell it to update it’s  
properties. Basically an object should be responsible for it’s data.  
There  
are many tutorials on OOP design on the web and I suggest that you take  
the  
time to read some of them. They are generally very good. The Pickaxe  
and  
Why’s Poignant guide are good. (Whys book is different but informative).  
[http://www.ruby-doc.org/docs/ProgrammingRuby/](http://www.ruby-doc.org/docs/ProgrammingRuby/)  
[http://poignantguide.net/ruby/](http://poignantguide.net/ruby/)

Other book resources for ruby can be found at  
[http://new.ruby-lang.org/en/documentation/book-list/](http://new.ruby-lang.org/en/documentation/book-list/)

This is a very important concept in Ruby since everything is an object  
and  
basically works this way. So an instance variable regarding status  
should  
be hidden from other objects, but accessible with instance methods to  
get  
status and set status. ie I ask an article, are you active? and it  
tells me  
if it is.

In rails whatever fields the db table has, the corresponding model will  
be  
endowed with getter and setter methods for each field automatically 🙂

That means that if you have a status field in your database table, then  
the  
model will already have the methods required to access it and set it.

@my\_model.status # returns the status variable  
@my\_model.status = “inactive” # to set the status

To make it’s state persistant (save it to the db) @my\_model.save!

ActiveRecord is very nice for this. But this by itself doesn’t help you  
find them which I believe was the subject of your initial post. To do  
this  
you use the find method provided by the ActiveRecord class. Since you  
model  
inherits from this class, your model gets a find method too. If you  
have a  
time where you are regularly performing the same action for a given  
outcome,  
then convinience methods are good.

def self.active\_articles  
find(:all, :conditions =\> { :active =\> true }  
end

By declaring this you can now use  
Article.active\_articles

If you decide to change the definition of what makes an article active,  
you  
don’t need to surf your code and find everywhere you did

my\_method\_to\_find\_articles( “active” ) or  
find(:all, :conditions =\> { :active =\> true } )

which may appear many times in many files to change the logic.

If in your code you aske the Article class or some parent object to get  
all  
the active articles when you want them, then you can change your logic  
in  
one place whenever required.

def self.active\_articles  
find( :all, :conditions=\> { :active =\> true, :archive =\> false }  
end

This is commonly refered to as DRY (Don’t Repeat Yourself) and makes  
code  
more readable and maintainable.

I am certainly no expert on this. I am new to programming in general  
and  
it’s not my day job. I really suggest you try looking at the Wiki on  
[www.rubyonrails.org](http://www.rubyonrails.org) and also try to find some blogs about this stuff.  
People who know it much better than I do have put a lot of time into  
explaining these concepts and you can learn a lot by reading their  
blogs.  
The rails blog is a good source.  
[http://weblog.rubyonrails.org/](http://weblog.rubyonrails.org/)  
and they also link to good blogs to get you started.

Cheers

Was there more to your comment as it seems to have been cut off, I think