Rails - Nov 2005 - newbie: displaying a denormalized list of records.

I am trying to list my orders showing customer names rather than 
customer IDs.  I am not having much luck.


I have a table called orders, having a ''customer_id'' field.  I
also have
a table called customers, which has a field called ''id'', as
well as a
field called ''name''.

In the orders model, I specify that order belongs_to customer, and in 
the customer model, I specify that the customer has_many orders.

As a first shot, I assumed that in the list view for orders, I could 
replace the working line

               <td><%=h order.send(''customer_id'')
%></td>

with something like

               <td><%=h
order.send(''order.customer.name'') %></td>.

That didn''t work.

My current iteration defines the following method in order.rb

	def self.find_all_denormalized
		sql = "	SELECT orders.*,  						               customers.name as 
customerName
                        From orders left join customers
                                          on customer_id = customers.id 
"
		orders_denormalized = Order.find_by_sql(sql)
		return orders_denormalized
	end

and in order_controller.rdb, I have redefined list as

  def list
    @order_pages, @orders = paginate Order.find_all_denormalized, 
:per_page => 10
  end

This is not working.  I am getting a message like:

wrong constant name 
#<Order:0x394ba68>#<Order:0x394ba20>#<Order:0x394b9d8>#<Order:0x394b990>#<Order:0x394b948>

-------------------------------------------------------

Two questions:  why is my approach not working, and is there a 
fundamentally better (more Rails) way to do this?

Thanks in advance

Ed









-- 
Posted via http://www.ruby-forum.com/.

hi Ed,

I think part of your problem is that you''re using the built-in paginate
instead of this one:

def paginate_collection(collection, options = {})
     default_options = {:per_page => 10, :page => 1}
     options = default_options.merge options

     pages = Paginator.new self, collection.size, options[:per_page], 
options[:page]
     first = pages.current.offset
     last = [first + options[:per_page], collection.size].min
     slice = collection[first...last]
     return [pages, slice]
   end

You should use the above function anytime you want to paginate a 
collection returned from a custom query (just add this func to your 
application.rb).

As for the rails way to get the customer name, you should be able to do:

order.customer.name

anywhere you have an actual object named ''order'' (in which
case you
won''t need a custom query at all (or the alternate paginate method
above
(but it was included for future reference I suppose :)))).  This 
statement is actually calling a method named ''customer_id'' of
the order
object (see documentation on ''send'').

<%=h order.send(''customer_id'') %>

The reason why that part of your code isn''t working is because order
has
no method named ''customer.name''.  The proper way to do what
you intended
is:

<%=h order.customer.name %>

Hope this helps!
--Jonathan



Ed Schechter wrote:
> I am trying to list my orders showing customer names rather than 
> customer IDs.  I am not having much luck.
> 
> 
> I have a table called orders, having a ''customer_id''
field.  I also have
> a table called customers, which has a field called ''id'',
as well as a
> field called ''name''.
> 
> In the orders model, I specify that order belongs_to customer, and in 
> the customer model, I specify that the customer has_many orders.
> 
> As a first shot, I assumed that in the list view for orders, I could 
> replace the working line
> 
>                <td><%=h
order.send(''customer_id'') %></td>
> 
> with something like
> 
>                <td><%=h
order.send(''order.customer.name'') %></td>.
> 
> That didn''t work.
> 
> My current iteration defines the following method in order.rb
> 
> 	def self.find_all_denormalized
> 		sql = "	SELECT orders.*,  						               customers.name as 
> customerName
>                         From orders left join customers
>                                           on customer_id = customers.id 
> "
> 		orders_denormalized = Order.find_by_sql(sql)
> 		return orders_denormalized
> 	end
> 
> and in order_controller.rdb, I have redefined list as
> 
>   def list
>     @order_pages, @orders = paginate Order.find_all_denormalized, 
> :per_page => 10
>   end
> 
> This is not working.  I am getting a message like:
> 
> wrong constant name 
>
#<Order:0x394ba68>#<Order:0x394ba20>#<Order:0x394b9d8>#<Order:0x394b990>#<Order:0x394b948>
> 
> -------------------------------------------------------
> 
> Two questions:  why is my approach not working, and is there a 
> fundamentally better (more Rails) way to do this?
> 
> Thanks in advance
> 
> Ed

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