Hello, I''m fairly new to Ruby, but I am trying to understand the relationship between database structure and models. My difficulty is that I have five or so tables all linked together and their primary key column is a serial number The tables are a set of tables called: itemmasters products prices subprices imprints etc. products, prices, and subprices, imprints, etc. belong to itemmasters based on a serial number How can I get about linking them without having to have a column in itemmasters for each of the sub tables? For instance: product_id price_id subprice_id imprint_id This would be somewhat silly as they all contain the same information. Right? Thank you, Brian Anderson -- 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 rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
On Jun 30, 2008, at 9:17 AM, Brian Anderson wrote:> > Hello, > > I''m fairly new to Ruby, but I am trying to understand the relationship > between database structure and models. > > My difficulty is that I have five or so tables all linked together and > their > primary key column is a serial number > > The tables are a set of tables called: > > itemmasters > products > prices > subprices > imprints > etc. > > products, prices, and subprices, imprints, etc. belong to itemmasters > based > on a serial number > > How can I get about linking them without having to have a column in > itemmasters for each of the sub tables? > > For instance: > > product_id > price_id > subprice_id > imprint_id > > This would be somewhat silly as they all contain the same information. > Right?You could try playing around with primary_key() to set the primary key for the given table as well as adjusting foreign_key in your has_one relationships to point to that primary key. Not sure if that will get you into trouble or not :) --~--~---------~--~----~------------~-------~--~----~ 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 rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
In third normal relational design you would have the itemmaster_id in each of the dependent tables. That is also what happens when you define the belongs_to has_many relationships. There needs to be some column in the database to relate the items. What you bring up, each child id on the parent table is a star schema. Otherwise you have to denormalize your data design and just stuff everything into one table. On Jun 30, 11:17 am, Brian Anderson <rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:> Hello, > > I''m fairly new to Ruby, but I am trying to understand the relationship > between database structure and models. > > My difficulty is that I have five or so tables all linked together and > their > primary key column is a serial number > > The tables are a set of tables called: > > itemmasters > products > prices > subprices > imprints > etc. > > products, prices, and subprices, imprints, etc. belong to itemmasters > based > on a serial number > > How can I get about linking them without having to have a column in > itemmasters for each of the sub tables? > > For instance: > > product_id > price_id > subprice_id > imprint_id > > This would be somewhat silly as they all contain the same information. > Right? > > Thank you, > > Brian Anderson > -- > Posted viahttp://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 rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk-unsubscribe@googlegroups.com For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
Thanks, everyone for the responses. I think I am clearly conceptualizing
things wrongly.
All the tables have an ItemSerial field
I am getting an error saying "Couldn''t find Itemprice without an
ID"
This message comes up even despite the fact that this is my controller:
class ItempriceController < ApplicationController
def show
@itemprices = Itemprice.find(params[:ItemSerial])
end
end
I am not finding Itemprice by id according to the above, but still I get
this error.
In my view as a test I have the following:
<% @page_title = "#{@itemprices.Price1}" %>
I may be thinking about this whole thing wrong.
-Brian
Jorg Lueke wrote:> In third normal relational design you would have the itemmaster_id in
> each of the dependent tables.
> That is also what happens when you define the belongs_to has_many
> relationships.
> There needs to be some column in the database to relate the items.
>
> What you bring up, each child id on the parent table is a star schema.
>
> Otherwise you have to denormalize your data design and just stuff
> everything into one table.
>
>
>
> On Jun 30, 11:17�am, Brian Anderson
<rails-mailing-l...@andreas-s.net>
--
Posted via http://www.ruby-forum.com/.
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Rails expects the ID name to be a certain way, so if you use a different ID you have to map those columns. For a parent child relationship where the child belongs_to a given parent. The default ID rais expects is parent_id. For HABTM relationships you would need to create an intermediate table. If you are just doing a straight select from a single table try using all lower case? On Jun 30, 12:18 pm, Brian Anderson <rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:> Thanks, everyone for the responses. I think I am clearly conceptualizing > things wrongly. > > All the tables have an ItemSerial field > > I am getting an error saying "Couldn''t find Itemprice without an ID" > > This message comes up even despite the fact that this is my controller: > > class ItempriceController < ApplicationController > def show > @itemprices = Itemprice.find(params[:ItemSerial]) > end > end > > I am not finding Itemprice by id according to the above, but still I get > this error. > > In my view as a test I have the following: > > <% @page_title = "#...@itemprices.Price1}" %> > > I may be thinking about this whole thing wrong. > > -Brian > > Jorg Lueke wrote: > > In third normal relational design you would have the itemmaster_id in > > each of the dependent tables. > > That is also what happens when you define the belongs_to has_many > > relationships. > > There needs to be some column in the database to relate the items. > > > What you bring up, each child id on the parent table is a star schema. > > > Otherwise you have to denormalize your data design and just stuff > > everything into one table. > > > On Jun 30, 11:17�am, Brian Anderson <rails-mailing-l...@andreas-s.net> > > -- > Posted viahttp://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 rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk-unsubscribe@googlegroups.com For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
@Brian: Your code says: class ItempriceController < ApplicationController> def show > @itemprices = Itemprice.find(params[:ItemSerial]) > end > end > >The .find method on an ActiveRecord model finds by primary key. Without mapping your primary keys (either by doing it the way Rails wants you to or by overriding the primary key using the set_primary_key method, Rails will try to find by id. Each field in your table also gets two finders automatically created for it. In your case, you have a field called item_serial_number or something simlar... let''s call it serialnumber for this example. With that field, Rails creates two new methods on the class: Itemprice.find_by_serialnumber(15) ("select * from itemprice where serialnumber = 15 LIMIT 1") Itemprice.find_all_by_serialnumber(15) ("select * from itemprice where serialnumber = 15") So to get what you want, just do class ItempriceController < ApplicationController def show @itemprices = Itemprice.find_by_serialnumber(params[:ItemSerial]) end end You should grab some books on Ruby and Rails though... Rails can work with "legacy" schemas but it''s much more difficult if you''re just starting out. There are a lot of database conventions that Rails expects you to adhere to. Good luck and I hope this helped a bit. --~--~---------~--~----~------------~-------~--~----~ 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 rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---