# DRY and engines

**URL:** <https://www.ruby-forum.com/t/dry-and-engines/54297>\
**Category:** Engines\
**Created:** [February 28, 2006, 10:28pm UTC](https://www.ruby-forum.com/t/dry-and-engines/54297 "2006-02-28T22:28:47Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![masschel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/aca169/32.png) [@masschel](https://www.ruby-forum.com/u/masschel)\
**Post date:** [February 28, 2006, 10:28pm UTC](https://www.ruby-forum.com/t/dry-and-engines/54297/1 "2006-02-28T22:28:47Z")

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Hello,

I’m using the UserEngine in my Rails application, in casu Riki. In the  
page to create a new book, the administrator can select the book  
administrator for that book, or create a new one if it does not exists.  
In that case I link\_to /user/new, but in the normal case I get  
redirected to /user/list, whereas I would like to be redirected back to  
the /book/create page. I solved this in the following way:

1. I added at the top of my create.rhtml (or in the create action)  
session[‘return-to’] = ‘/books/create’

2. And I changed the new action in the user controller to

In that case I get redirected back to the create book page. This is one  
way, but I have the feeling that it is not the most elegant. I could of  
course copy the complete new action, but this goes against the DRY  
principle, and against the reusability of Engines. In the end, I might  
have copied all code inside my rails application. This follows a  
discussion I had with Jay:

> Another thing to think about: You want the engine to be easily  
> extensible without folks having to modify the actual engine files, or  
> cut-and-paste \>huge swaths of code. So keeping subroutines short (and  
> thus keeping overrides granular) is even more important than it is in  
> “normal” code. \>UserEngine does a good job of keeping the “core” code  
> under lib, but I still found I had to copy an entire action from  
> user\_controller just to change \>one string. I’m not sure I can think of  
> specific patterns to encourage for extensibility, but it’s something  
> that should be kept in mind.

Or there other ways to solve this, I mean, reusing engine code  
efficiently?

By the way, I still have then another problem in this way. When the  
administrator has already filled in some fields of the form, they get  
lost when he gets back to the create page. I know this is probably more  
a Rails question in general, but does anybody has some ideas on how to  
keep the field data? My gutfeeling is that it is lost, unless I  
integrate it all together, by integrating the new user partial into the  
create form, and duplicating the user/new code.

How could this be rewritten, so the new action of the user controller  
could be reused? Or is this not the purpose of Engines, and maybe more  
of plug-ins, where Engines are meant to be more complete applications?

enjoy!

Bart

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<div class="post-metadata">

**Author:** ![masschel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/aca169/32.png) [@masschel](https://www.ruby-forum.com/u/masschel)\
**Post date:** [February 28, 2006, 10:32pm UTC](https://www.ruby-forum.com/t/dry-and-engines/54297/2 "2006-02-28T22:32:48Z")

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Both the User and Login engines could do with serious refactoring with  
a view to making them much cleaner in terms of overriding behaviour. A  
big part of this is probably going to be establishing a clear API for  
both. Let the discussion commence!

- james

On 2/28/06, Bart M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> ```
> session['return-to'] = '/books/create'
> 
> ```
> 
> course copy the complete new action, but this goes against the DRY  
> user\_controller just to change \>one string. I’m not sure I can think of  
> integrate it all together, by integrating the new user partial into the  
> Bart
> 
> * * *
> 
> engine-users mailing list  
> removed\_email\_address@domain.invalid  
> [http://lists.rails-engines.org/listinfo.cgi/engine-users-rails-engines.org](http://lists.rails-engines.org/listinfo.cgi/engine-users-rails-engines.org)

–

- J \*  
~

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<div class="post-metadata">

**Author:** ![masschel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/aca169/32.png) [@masschel](https://www.ruby-forum.com/u/masschel)\
**Post date:** [February 28, 2006, 11:02pm UTC](https://www.ruby-forum.com/t/dry-and-engines/54297/3 "2006-02-28T23:02:08Z")

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Hi,

Ok, I will try a bit more how far I can go with this  
session[‘return-to’] idea, which is already used nicely in the  
LoginEngine, and see how it can be usefull for this process.

And I had to reread Chapter 8 of the pragmatic programmer book to  
realize that sessions will also solve my other, non-engine related  
problem…

Bart

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<div class="post-metadata">

**Author:** ![masschel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/aca169/32.png) [@masschel](https://www.ruby-forum.com/u/masschel)\
**Post date:** [March 1, 2006, 7:20pm UTC](https://www.ruby-forum.com/t/dry-and-engines/54297/4 "2006-03-01T19:20:17Z")

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Hello,

I found a solution for my problem, and even better then I thought. It  
should be general enough for other uses. It works in two directions:

1. you can say where the user/new has to return to, after completion (in  
my case, back to the book creation)

2. In my book/create, I get immediately the id of the newly created  
user, so I can use it in my book/create form. The administrator does not  
have to select it again.

For doing this I changed the following lines in the user\_controller of  
the UserEngine:

redirect\_to :action =\> ‘list’

changed to

```
          if session['return-to']
            session['return-to'][:new_user_id] = @user.id
            redirect_to( session['return-to'] )
          else
            redirect_to :action => 'list'
          end

```

My book/create action, looks like this:

def create  
case request.method  
when :get  
@book = partially\_created\_book  
@all\_users\_mapped = User.find\_all.map { |c| ["#{c.fullname}",  
c.id] }  
if !params[:new\_user\_id].nil? # retrieve the newly created  
user.  
@admin = User.find(params[:new\_user\_id])  
end  
when :post  
if params[:commit]==“Create new user”  
session[:partially\_created\_book] = Book.new(params[:book])  
session[‘return-to’] = {:controller =\> ‘books’, :action =\>  
‘create’} # to set the action where to return to  
redirect\_to :controller =\> ‘user’, :action =\> ‘new’  
elsif params[:commit]==“Create”  
Book.create(params[:book])  
redirect\_to ‘/’ + params[:book][:url\_name]  
end  
end  
end

It works, and seems general enough. For the full code, you’ll have to  
wait for Riki 0.3.1, coming soon…

Any ideas to improve this?

Bart

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<div class="post-metadata">

**Author:** ![masschel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/aca169/32.png) [@masschel](https://www.ruby-forum.com/u/masschel)\
**Post date:** [March 1, 2006, 8:25pm UTC](https://www.ruby-forum.com/t/dry-and-engines/54297/5 "2006-03-01T20:25:10Z")

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Hi!

In attendance of the new post, I can already say that indeed that was  
the first way I did it, but it did not give me back the newly created  
user. And that was something which I found quite user-friendly, putting  
this newly created information directly in the form of creating the  
book.

Just extending the general usage a bit…

bart

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<div class="post-metadata">

**Author:** ![masschel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/aca169/32.png) [@masschel](https://www.ruby-forum.com/u/masschel)\
**Post date:** [March 1, 2006, 7:40pm UTC](https://www.ruby-forum.com/t/dry-and-engines/54297/6 "2006-03-01T19:40:26Z")

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> Any ideas to improve this?
> 
> Bart  
> Hi Bart!

I was writing an answer while you have added yours.  
I can still publish it as a general suggestion. Here it is:

"…  
I don’t have a final solution there, but rather a small suggestion:

avoid the if/else construct and just set the  
session[‘return-to’] ||= ‘/your\_controller/list’  
as default.

In this way you just  
redirect\_to session[‘return-to’]  
whenever you need it. It scales better, doesn’t  
matter how many new spacial cases you want to introduce.  
…"

About the DRYness I create a new POST so that we don’t confuse the Riki  
specific issue to the genear problem.

See you in the new post 😉

Mauro