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david.harris.uk

2007-Aug-30 20:31 UTC

Rails - depot application

I''m doing the depot example in the Agle Web development book.
I''m
getting this error:

"undefined method `product'' for
#<BigDecimal:331ce70,''0.21E1'',8(8)>  "

"Extracted source (around line #9):

8: for item in @items
9: 	product = item.product
10: -%>
11:   <tr>
12:   <td><%= item.product%></td>"
this is display_cart.rhtml

line_item.rb has:

"class LineItem < ActiveRecord::Base
	belongs_to :product

	def self.for_product(product)
		item = self.new
		item.quantity = 1
		item.product = product
		item.unit_price = product.price
	end
end  "

cart.rb has:

"class Cart

attr_reader :items
attr_reader :total_price

 def initialize
   @items = []
   @total_price = 0.0
 end

 def add_product(product)
   @items << LineItem.for_product(product)
   @total_price += product.price
 end
end   "


It looks like product = item.product in display_cart.rhtml is pulling
out a decimal number not a content array item. But I have no great
idea why or how to find out what is being put into @items in the cart
class.

I haven''t been able to find a Google solution to this and I dont
*think* I have any typos (the downloaded sample files from the Agiles
site at pragmaticprogrammer produces the same error)


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Louis Rose

2007-Aug-31 09:28 UTC

head link

Re: Rails - depot application

On Aug 30, 9:31 pm, "david.harris.uk"
<david.harris...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> I''m doing the depot example in the Agle Web development book.
I''m
> getting this error:
>
> "undefined method `product'' for
#<BigDecimal:331ce70,''0.21E1'',8(8)>  "
>
> "Extracted source (around line #9):
>
> 8: for item in @items
> 9:      product = item.product
> 10: -%>
> 11:   <tr>
> 12:   <td><%= item.product%></td>"
> this is display_cart.rhtml
>
> line_item.rb has:
>
> "class LineItem < ActiveRecord::Base
>         belongs_to :product
>
>         def self.for_product(product)
>                 item = self.new
>                 item.quantity = 1
>                 item.product = product
>                 item.unit_price = product.price
>         end
> end  "
>
> cart.rb has:
>
> "class Cart
>
> attr_reader :items
> attr_reader :total_price
>
>  def initialize
>    @items = []
>    @total_price = 0.0
>  end
>
>  def add_product(product)
>    @items << LineItem.for_product(product)
>    @total_price += product.price
>  end
> end   "
>
> It looks like product = item.product in display_cart.rhtml is pulling
> out a decimal number not a content array item. But I have no great
> idea why or how to find out what is being put into @items in the cart
> class.
>
> I haven''t been able to find a Google solution to this and I dont
> *think* I have any typos (the downloaded sample files from the Agiles
> site at pragmaticprogrammer produces the same error)
Hi David,

Here''s my guess:

"undefined method `product'' for
#<BigDecimal:331ce70,''0.21E1'',8(8)>"
means that Ruby''s trying to call the method product on a BigDecimal.
On line 9 (where the error orginates), product is being called on the
variable item. Item is an element of the @items array. @items is being
built in the add_product method of the Cart class, by calling
for_product(product) on LineItem. And this is where I think the
problem is: the last line of the for_product(product) method assigns a
price to the item variable.

Every expression in Ruby returns a value. The value returned from
performing an assignment is what the right-hand side of the expression
evaluates to. Furthermore, the last expression in a Ruby method is the
return value of that method. So, instead of returning a LineItem from
the for_product(product) method, this code is actually returning the
value of the price variable, a BigDecimal.

In short, I believe the following code will fix your problem:

def self.for_product(product)
  item = self.new
  item.quantity = 1
  item.product = product
  item.unit_price = product.price
  item
end

If you find this idiom confusing (I know I do), you may use the return
keyword (although hard-core Rubyists may frown upon it!):

def self.for_product(product)
  item = self.new
  item.quantity = 1
  item.product = product
  item.unit_price = product.price
  return item
end

Cheers,
Louis.

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david.harris.uk

2007-Sep-06 18:54 UTC

head link

Re: Rails - depot application

I''m still getting "undefined method `product'' for
#<BigDecimal:
331ce70,''0.21E1'',8(8)>  "

So this promising idea didnt work. I altered display_cart.rhtml thus:

"<table>

<%
for item in @items
	@dbg = item.type
	@v1=item.methods
	@v2= item.instance_variables
-%>
  <tr>"

which gives:
"
wibble: LineItem instance variables: @attributes@new_record@product *
methods: before_createcreate_or_updatesave_with_validation[stuff]
"

So item is a LineItem class not a decimal and this looks like an
ActiveRecord class.

Which makes me wonder if this application ever worked: it''s not a typo
by me I think since I downloaded the source from the website and get
the same error, but I seem to be the only one having this problem. So
I don;t know. I think I''ll dump the example from the book since I seem
to be spending more time debugging it than learning Rails!

On Aug 31, 11:28 am, Louis Rose
<louismr...-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org>
wrote:> On Aug 30, 9:31 pm, "david.harris.uk"
<david.harris...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> wrote:
>
>
>
> > I''m doing the depot example in the Agle Web development book.
I''m
> > getting this error:
>
> > "undefined method `product'' for
#<BigDecimal:331ce70,''0.21E1'',8(8)>  "
>
> > "Extracted source (around line #9):
>
> > 8: for item in @items
> > 9:      product = item.product
> > 10: -%>
> > 11:   <tr>
> > 12:   <td><%= item.product%></td>"
> > this is display_cart.rhtml
>
> > line_item.rb has:
>
> > "class LineItem < ActiveRecord::Base
> >         belongs_to :product
>
> >         def self.for_product(product)
> >                 item = self.new
> >                 item.quantity = 1
> >                 item.product = product
> >                 item.unit_price = product.price
> >         end
> > end  "
>
> > cart.rb has:
>
> > "class Cart
>
> > attr_reader :items
> > attr_reader :total_price
>
> >  def initialize
> >    @items = []
> >    @total_price = 0.0
> >  end
>
> >  def add_product(product)
> >    @items << LineItem.for_product(product)
> >    @total_price += product.price
> >  end
> > end   "
>
> > It looks like product = item.product in display_cart.rhtml is pulling
> > out a decimal number not a content array item. But I have no great
> > idea why or how to find out what is being put into @items in the cart
> > class.
>
> > I haven''t been able to find a Google solution to this and I
dont
> > *think* I have any typos (the downloaded sample files from the Agiles
> > site at pragmaticprogrammer produces the same error)
>
> Hi David,
>
> Here''s my guess:
>
> "undefined method `product'' for
#<BigDecimal:331ce70,''0.21E1'',8(8)>"
> means that Ruby''s trying to call the method product on a
BigDecimal.
> On line 9 (where the error orginates), product is being called on the
> variable item. Item is an element of the @items array. @items is being
> built in the add_product method of the Cart class, by calling
> for_product(product) on LineItem. And this is where I think the
> problem is: the last line of the for_product(product) method assigns a
> price to the item variable.
>
> Every expression in Ruby returns a value. The value returned from
> performing an assignment is what the right-hand side of the expression
> evaluates to. Furthermore, the last expression in a Ruby method is the
> return value of that method. So, instead of returning a LineItem from
> the for_product(product) method, this code is actually returning the
> value of the price variable, a BigDecimal.
>
> In short, I believe the following code will fix your problem:
>
> def self.for_product(product)
>   item = self.new
>   item.quantity = 1
>   item.product = product
>   item.unit_price = product.price
>   item
> end
>
> If you find this idiom confusing (I know I do), you may use the return
> keyword (although hard-core Rubyists may frown upon it!):
>
> def self.for_product(product)
>   item = self.new
>   item.quantity = 1
>   item.product = product
>   item.unit_price = product.price
>   return item
> end
>
> Cheers,
> Louis.

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Louis Rose

2007-Sep-07 08:50 UTC

head link

Re: Rails - depot application

On Sep 6, 7:54 pm, "david.harris.uk"
<david.harris...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:> I''m still getting "undefined method `product'' for
#<BigDecimal:
> 331ce70,''0.21E1'',8(8)>  "
>
> So this promising idea didnt work. I altered display_cart.rhtml thus:
>
> "<table>
>
> <%
> for item in @items
>         @dbg = item.type
>         @v1=item.methods
>         @v2= item.instance_variables
> -%>
>   <tr>"
>
> which gives:
> "
> wibble: LineItem > instance variables: @attributes@new_record@product *
> methods: before_createcreate_or_updatesave_with_validation[stuff]
> "
>
> So item is a LineItem class not a decimal and this looks like an
> ActiveRecord class.
>
> Which makes me wonder if this application ever worked: it''s not a
typo
> by me I think since I downloaded the source from the website and get
> the same error, but I seem to be the only one having this problem. So
> I don;t know. I think I''ll dump the example from the book since I
seem
> to be spending more time debugging it than learning Rails!
>
> On Aug 31, 11:28 am, Louis Rose
<louismr...-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org> wrote:
>
> > On Aug 30, 9:31 pm, "david.harris.uk"
<david.harris...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> > wrote:
>
> > > I''m doing the depot example in the Agle Web development
book. I''m
> > > getting this error:
>
> > > "undefined method `product'' for
#<BigDecimal:331ce70,''0.21E1'',8(8)>  "
>
> > > "Extracted source (around line #9):
>
> > > 8: for item in @items
> > > 9:      product = item.product
> > > 10: -%>
> > > 11:   <tr>
> > > 12:   <td><%= item.product%></td>"
> > > this is display_cart.rhtml
>
> > > line_item.rb has:
>
> > > "class LineItem < ActiveRecord::Base
> > >         belongs_to :product
>
> > >         def self.for_product(product)
> > >                 item = self.new
> > >                 item.quantity = 1
> > >                 item.product = product
> > >                 item.unit_price = product.price
> > >         end
> > > end  "
>
> > > cart.rb has:
>
> > > "class Cart
>
> > > attr_reader :items
> > > attr_reader :total_price
>
> > >  def initialize
> > >    @items = []
> > >    @total_price = 0.0
> > >  end
>
> > >  def add_product(product)
> > >    @items << LineItem.for_product(product)
> > >    @total_price += product.price
> > >  end
> > > end   "
>
> > > It looks like product = item.product in display_cart.rhtml is
pulling
> > > out a decimal number not a content array item. But I have no
great
> > > idea why or how to find out what is being put into @items in the
cart
> > > class.
>
> > > I haven''t been able to find a Google solution to this
and I dont
> > > *think* I have any typos (the downloaded sample files from the
Agiles
> > > site at pragmaticprogrammer produces the same error)
>
> > Hi David,
>
> > Here''s my guess:
>
> > "undefined method `product'' for
#<BigDecimal:331ce70,''0.21E1'',8(8)>"
> > means that Ruby''s trying to call the method product on a
BigDecimal.
> > On line 9 (where the error orginates), product is being called on the
> > variable item. Item is an element of the @items array. @items is being
> > built in the add_product method of the Cart class, by calling
> > for_product(product) on LineItem. And this is where I think the
> > problem is: the last line of the for_product(product) method assigns a
> > price to the item variable.
>
> > Every expression in Ruby returns a value. The value returned from
> > performing an assignment is what the right-hand side of the expression
> > evaluates to. Furthermore, the last expression in a Ruby method is the
> > return value of that method. So, instead of returning a LineItem from
> > the for_product(product) method, this code is actually returning the
> > value of the price variable, a BigDecimal.
>
> > In short, I believe the following code will fix your problem:
>
> > def self.for_product(product)
> >   item = self.new
> >   item.quantity = 1
> >   item.product = product
> >   item.unit_price = product.price
> >   item
> > end
>
> > If you find this idiom confusing (I know I do), you may use the return
> > keyword (although hard-core Rubyists may frown upon it!):
>
> > def self.for_product(product)
> >   item = self.new
> >   item.quantity = 1
> >   item.product = product
> >   item.unit_price = product.price
> >   return item
> > end
>
> > Cheers,
> > Louis.
Hi David,

Do you print the class name, instance variables and methods for every
element of the @items array? I suspect that majority of the array
contains LineItem objects, but one of the elements is a BigDecimal.

You could try changing the code as I suggested above, deleting all of
the data from your database, and trying again.

Cheers,
Louis.


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