Rails - Sep 2005 - Auto-Save on n:m Relation Prevents Preview Function?

Hi

I want to implement the following:

I have an Article ActiveRecord with title and body. I also have an  
Author ActiveRecord with a "name" property. There is an n:m relations
between Author and Article.

I have an ArticleController that implements CRUD for Article  
datasets. This controller has the "classic" actions: new, create,  
edit, update, delete, destroy, list. I want to be able to post to  
"create", with a "Preview" button that will then preview the
changes
made to the Article. The Article edit form also includes a list you  
can select the authors of this Article from.

For the title and body, this is no problem since these fields are  
only updated in the database when I call @article.save. However, for  
n:m relations, this is different; the changes are reflected to the  
database immediately (also see AR documentation at http://tinyurl.com/ 
aujwb).

Is there an elegant way to do this preview or will I have to store  
things in the session and push them into another template variable.  
I''d like if it not comes to this since I hoped to do things  
consistently with an DB abstraction layer like ActiveRecord.

Regards

Manuel Holtgrewe

Manuel Holtgrewe wrote:
> I have an Article ActiveRecord with title and body. I also have an  
> Author ActiveRecord with a "name" property. There is an n:m
relations
> between Author and Article.
> 
> I have an ArticleController that implements CRUD for Article  datasets. 
> This controller has the "classic" actions: new, create,  edit,
update,
> delete, destroy, list. I want to be able to post to  "create",
with a
> "Preview" button that will then preview the changes  made to the 
> Article. The Article edit form also includes a list you  can select the 
> authors of this Article from.
> 
> For the title and body, this is no problem since these fields are  only 
> updated in the database when I call @article.save. However, for  n:m 
> relations, this is different; the changes are reflected to the  database 
> immediately (also see AR documentation at http://tinyurl.com/ aujwb).
> 
> Is there an elegant way to do this preview or will I have to store  
> things in the session and push them into another template variable. 
I''d
> like if it not comes to this since I hoped to do things  consistently 
> with an DB abstraction layer like ActiveRecord.
As suggested on p.232 of the Agile book, how about turning the join table
into an "Authorship" model, and the HABTM relations into HM relations,
on
which you can use the build method to create the structure without auto-save?


-- 
We develop, watch us RoR, in numbers too big to ignore.

Am 17.09.2005 um 22:28 schrieb Mark Reginald James:
> As suggested on p.232 of the Agile book, how about turning the join  
> table
> into an "Authorship" model, and the HABTM relations into HM  
> relations, on
> which you can use the build method to create the structure without  
> auto-save?
Thanks for your interest in my problem. However, this does not help  
when you want to remove elements from a relation. There seems to be  
no equivalent of build for removing elements from a collection.

Regards

Manuel Holtgrewe

Manuel Holtgrewe wrote:
> 
> Am 17.09.2005 um 22:28 schrieb Mark Reginald James:
> 
>> As suggested on p.232 of the Agile book, how about turning the join  
>> table
>> into an "Authorship" model, and the HABTM relations into HM  
>> relations, on
>> which you can use the build method to create the structure without  
>> auto-save?
> 
> Thanks for your interest in my problem. However, this does not help  
> when you want to remove elements from a relation. There seems to be  no 
> equivalent of build for removing elements from a collection.
Looking at the AR code you could use association.to_ary.delete(model_instance)
to get the right association object array for your preview views.

-- 
We develop, watch us RoR, in numbers too big to ignore.

Am 17.09.2005 um 23:18 schrieb Mark Reginald James:
> Looking at the AR code you could use association.to_ary.delete 
> (model_instance)
> to get the right association object array for your preview views.
If I understand you right, I''d assing the value of the changed array  
in another template variable then? This is not really optimal in my  
opinion. This seems to be equal to do something like "@authors =  
model.authors". Additionally, I don''t get model validation that
way.

Regards

Manuel Holtgrewe

On 15-sep-2005, at 22:10, Manuel Holtgrewe wrote:
>
> Is there an elegant way to do this preview or will I have to store  
> things in the session and push them into another template variable.  
> I''d like if it not comes to this since I hoped to do things  
> consistently with an DB abstraction layer like ActiveRecord.
You will. As an option just store the whole record in the session  
when editing.

-- 
Julian "Julik" Tarkhanov

Manuel Holtgrewe wrote:
> 
> Am 17.09.2005 um 23:18 schrieb Mark Reginald James:
> 
>> Looking at the AR code you could use association.to_ary.delete 
>> (model_instance)
>> to get the right association object array for your preview views.
> 
> 
> If I understand you right, I''d assing the value of the changed
array  in
> another template variable then? This is not really optimal in my  
> opinion. This seems to be equal to do something like "@authors =  
> model.authors". Additionally, I don''t get model validation
that way.
No the real association array variable is used, but it doesn''t
mess with the DB. Like:

class Article
   has_many :authors

   def add_author(author, preview=false)
     if preview
        self.authors.to_ary << author
     else
        self.authors << author
     end
   end

   def del_author(author, preview=false)
     if preview
        self.authors.to_ary.delete(author)
     else
        self.authors.delete(author)
     end
   end

end

class ArticleController

private
   def build_article(params, preview)
     @article = ...
     @article.add_author( Author.new(params[''Author1'']),
preview )
     @article.del_author( Author.find(34), preview )
   end

public
   def show_preview
     build_article(params,true)
     if @article.valid? ...
   end

   def show_final
     build_article(params,false)
     if @article.save ...
   end

end

Then in both views either use @article.authors, which is
cached, or set @authors = @article.authors at the end of
build_article. Should work with both HABTM and HM.


-- 
We develop, watch us RoR, in numbers too big to ignore.

Am 18.09.2005 um 02:12 schrieb Julian ''Julik'' Tarkhanov:
>
> On 15-sep-2005, at 22:10, Manuel Holtgrewe wrote:
>
>>
>> Is there an elegant way to do this preview or will I have to store  
>> things in the session and push them into another template  
>> variable. I''d like if it not comes to this since I hoped to do
>> things consistently with an DB abstraction layer like ActiveRecord.
>>
>
> You will. As an option just store the whole record in the session  
> when editing.
Then I lose validation through the ActiveRecord model.

Regards

Manuel Holtgrewe