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linda Keating

2011-May-08 17:00 UTC

Beginners question | moving a method from controller to model

I''m learning with the Agile Web Development 4th edition book. 
I''ve
built a method in my controller to test that it works, and now I want to
move it to the model.
********************************
*** line_item controller ***
********************************
def create
    @cart = current_cart
     event = Event.find(params[:event_id])
     @line_item = @cart.add_event(event)
      new_capacity = event.capacity


    respond_to do |format|
      if @line_item.save
        new_capacity =  new_capacity - @line_item.quantity
        event.capacity = new_capacity
        event.save

        format.html { redirect_to(@line_item.cart, :notice => ''Line
item
was successfully created.'') }
        format.xml  { render :xml => @line_item, :status => :created,
:location => @line_item }
      else
        format.html { render :action => "new" }
        format.xml  { render :xml => @line_item.errors, :status =>
:unprocessable_entity }
      end
    end
  end

so I started by doing this

***********************************
*****line_item.rb****************
********************************

def  decrease_seat_capacity_on_create

      new_capacity =  new_capacity - @line_item.quantity
      event.capacity = new_capacity
      event.save
  end

and made a changed the line_item controller like this

respond_to do |format|
      if @line_item.save
        @line_item.decrease_seat_capacity_on_create


But I get the error

undefined method `quantity'' for nil:NilClass
Rails.root: c:/webtech/ServerSide/tickets_online

Application Trace | Framework Trace | Full Trace
app/models/line_item.rb:12:in `decrease_seat_capacity_on_create''
app/controllers/line_items_controller.rb:51:in `block in create''
app/controllers/line_items_controller.rb:49:in `create''


So I''m a bit confused about ''quantity''. 
I''ve used it in another method
in the line_item.rb and it worked (much to my surprise) but it doesn''t
work in this new method I''m writing.

I really am an absolute beginner so I''m really just guessing most of
the
time.  Any suggestions or hints would be most appreciated.

thanks in advance for your patience.

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David Kahn

2011-May-08 17:32 UTC

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Re: Beginners question | moving a method from controller to model

On Sun, May 8, 2011 at 12:00 PM, linda Keating
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> wrote:
> I''m learning with the Agile Web Development 4th edition book. 
I''ve
> built a method in my controller to test that it works, and now I want to
> move it to the model.
> ********************************
> *** line_item controller ***
> ********************************
> def create
>    @cart = current_cart
>     event = Event.find(params[:event_id])
>     @line_item = @cart.add_event(event)
>      new_capacity = event.capacity
>
>
>    respond_to do |format|
>      if @line_item.save
>        new_capacity =  new_capacity - @line_item.quantity
>        event.capacity = new_capacity
>        event.save
>
>        format.html { redirect_to(@line_item.cart, :notice =>
''Line item
> was successfully created.'') }
>        format.xml  { render :xml => @line_item, :status => :created,
> :location => @line_item }
>      else
>        format.html { render :action => "new" }
>        format.xml  { render :xml => @line_item.errors, :status =>
> :unprocessable_entity }
>      end
>    end
>  end
>
> so I started by doing this
>
> ***********************************
> *****line_item.rb****************
> ********************************
>
> def  decrease_seat_capacity_on_create
>
>      new_capacity =  new_capacity - @line_item.quantity
>      event.capacity = new_capacity
>      event.save
>  end
>
In this method @line_item does not exist because you have not created it. So
you may need to pass to this method the line_item object or look it up.

Also, you should look at the after_save callback in ActiveRecord, that way
you *might* be able to tell your LineItem model to automatically perform
this action after a successful save (if you google for activerecord
callbacks you will find a number of them, they are very useful).

>
> and made a changed the line_item controller like this
>
> respond_to do |format|
>      if @line_item.save
>        @line_item.decrease_seat_capacity_on_create
>
>
> But I get the error
>
> undefined method `quantity'' for nil:NilClass
> Rails.root: c:/webtech/ServerSide/tickets_online
>
> Application Trace | Framework Trace | Full Trace
> app/models/line_item.rb:12:in `decrease_seat_capacity_on_create''
> app/controllers/line_items_controller.rb:51:in `block in create''
> app/controllers/line_items_controller.rb:49:in `create''
>
>
> So I''m a bit confused about ''quantity''. 
I''ve used it in another method
> in the line_item.rb and it worked (much to my surprise) but it
doesn''t
> work in this new method I''m writing.
>
> I really am an absolute beginner so I''m really just guessing most
of the
> time.  Any suggestions or hints would be most appreciated.
>
> thanks in advance for your patience.
>
> --
> Posted via http://www.ruby-forum.com/.
>
> --
> You received this message because you are subscribed to the Google Groups
> "Ruby on Rails: Talk" group.
> To post to this group, send email to
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> To unsubscribe from this group, send email to
>
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> http://groups.google.com/group/rubyonrails-talk?hl=en.
>
>
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Jeffrey L. Taylor

2011-May-08 18:00 UTC

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Re: Beginners question | moving a method from controller to model

See inserted comments below.

Quoting linda Keating
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>:> I''m learning with the Agile Web Development 4th edition book. 
I''ve
> built a method in my controller to test that it works, and now I want to
> move it to the model.
> ********************************
> *** line_item controller ***
> ********************************
> def create
>     @cart = current_cart
>      event = Event.find(params[:event_id])
>      @line_item = @cart.add_event(event)
>       new_capacity = event.capacity
> 
> 
>     respond_to do |format|
>       if @line_item.save
>         new_capacity =  new_capacity - @line_item.quantity
>         event.capacity = new_capacity
>         event.save
> 
>         format.html { redirect_to(@line_item.cart, :notice =>
''Line item
> was successfully created.'') }
>         format.xml  { render :xml => @line_item, :status => :created,
> :location => @line_item }
>       else
>         format.html { render :action => "new" }
>         format.xml  { render :xml => @line_item.errors, :status =>
> :unprocessable_entity }
>       end
>     end
>   end
> 
> so I started by doing this
> 
> ***********************************
> *****line_item.rb****************
> ********************************
> 
> def  decrease_seat_capacity_on_create
> 
>       new_capacity =  new_capacity - @line_item.quantity
>       event.capacity = new_capacity
>       event.save
>   end
> 
new_capacity and event are local variables in the controller method.  They are
not accessible in the called model method.  @line_item is an instance variable
of the controller instance.  It is also not accessible in the model method.
However it references the same object as self in the model method.
Presumably, event is another model.  Note: it is possible that a LineItem has
an event method because there is an association between Events and LineItems.

I don''t see any good reason to push this functionality into a model
method.
The only property of the model that is clearly being used is the quantity
attribute/method.  Unless the LineItem model includes a reference to an Event
(i.e. LineItem belongs to an Event or hasMany Events).  It still looks like
poor design unless there are several factors not mentioned here.

Jeffrey
> and made a changed the line_item controller like this
> 
> respond_to do |format|
>       if @line_item.save
>         @line_item.decrease_seat_capacity_on_create
> 
> 
> But I get the error
> 
> undefined method `quantity'' for nil:NilClass
> Rails.root: c:/webtech/ServerSide/tickets_online
> 
> Application Trace | Framework Trace | Full Trace
> app/models/line_item.rb:12:in `decrease_seat_capacity_on_create''
> app/controllers/line_items_controller.rb:51:in `block in create''
> app/controllers/line_items_controller.rb:49:in `create''
> 
> 
> So I''m a bit confused about ''quantity''. 
I''ve used it in another method
> in the line_item.rb and it worked (much to my surprise) but it
doesn''t
> work in this new method I''m writing.
> 
It isn''t quantity that isn''t working, it is that @line_item is
nil (i.e.,
@line_item of the LineItem instance has not been assigned a value).
@line_item is an instance variable in the controller, not in the model.
> I really am an absolute beginner so I''m really just guessing most
of the
> time.  Any suggestions or hints would be most appreciated.
HTH,
  Jeffrey

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Ruby Tuesday

2011-May-08 19:09 UTC

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Re: Beginners question | moving a method from controller to model

Jeffrey L. Taylor wrote in post #997405:> See inserted comments below.
>
> Quoting linda Keating
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>:
>>       new_capacity = event.capacity
>>         format.xml  { render :xml => @line_item, :status =>
:created,
>>
>>
> new_capacity and event are local variables in the controller method.
> They are
> not accessible in the called model method.  @line_item is an instance
> variable
> of the controller instance.  It is also not accessible in the model
> method.
> However it references the same object as self in the model method.
> Presumably, event is another model.  Note: it is possible that a
> LineItem has
> an event method because there is an association between Events and
> LineItems.
>
> I don''t see any good reason to push this functionality into a
model
> method.
> The only property of the model that is clearly being used is the
> quantity
> attribute/method.  Unless the LineItem model includes a reference to an
> Event
> (i.e. LineItem belongs to an Event or hasMany Events).  It still looks
> like
> poor design unless there are several factors not mentioned here.
>
Hi Jeffrey, I was moving it into the model soley because I''ve read that
fat models and skinny controllers are the best design practice.  I was 
just trying to get the function to work first, and now that it''s
working
I was hoping to tidy up the design.  But maybe I should just leave it as 
is.  I have though similar functionality in the update controller that 
looks like this ...


def update
    @line_item = LineItem.find(params[:id])
    event = @line_item.event
    new_quantity = params[:line_item_quantity].to_i
    change_in_capacity = @line_item.quantity - new_quantity

    respond_to do |format|
      if @line_item.update_attributes(params[:line_item])
        if (@line_item.quantity >0)
         event.capacity = change_in_capacity
         event.save


and I''ll be writing something similar again reversing the action in the
destroy method of line_item.

But maybe I should just leave it as is for the moment until I''ve
learned
a bit more about Ruby and Rails.


Many thanks for your help and feedback.  Really appreciate your 
patience.

Linda
> Jeffrey
>
>> Rails.root: c:/webtech/ServerSide/tickets_online
>>
> It isn''t quantity that isn''t working, it is that
@line_item is nil
> (i.e.,
> @line_item of the LineItem instance has not been assigned a value).
> @line_item is an instance variable in the controller, not in the model.
>
>> I really am an absolute beginner so I''m really just guessing
most of the
>> time.  Any suggestions or hints would be most appreciated.
>
> HTH,
>   Jeffrey
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Rails - May 2011 - Beginners question | moving a method from controller to model

Beginners question | moving a method from controller to model

Re: Beginners question | moving a method from controller to model

Re: Beginners question | moving a method from controller to model

Re: Beginners question | moving a method from controller to model