Re: Structuring Active Record relationships

Sharagoz
Wed, 12 May 2010 07:58:54 -0000

Expense would belong to Vendor, not have one Vendor, unless you are
planning to put the foreign key in the vendors table, which sounds
very strange, as that would require a new vendor to be created for
every expense.
If you are fist selecting a vendor, and then selecting an account
belonging to that vendor when you create an expense, then it makes
sense to hook expense up to account, not vendor.

class Vendor
  has_many :accounts

class Account
  belongs_to :vendor
  has_many :expenses

class Expense
  belongs_to :account

Then when you have created an expense you can get its account through
@expense.account and its vendor through @expense.account.vendor.
Does this make sense?

On May 12, 3:22 am, RichardOnRails
<RichardDummyMailbox58...-FtJgd9dCuO3JTKoYRCtP1UEOCMrvLtNR@public.gmane.org>
wrote:
> Thinking about it some more,  I now think I should have separate
> Expense, Vendor and Account tables with the following relationships:
>
> class Expense
>         has_one Vendor
>
> class Vendor
>         has_many Accounts
>         belongs_to Expense
>
> class Account
>         belongs_to Vendor
>
> Then an Expense record can get Accounts through Vendor. .. or
> something like that.
>
> Am I getting warmer?
>
> Thanks in Advance,
> Richard
>
> On May 11, 8:57 pm, RichardOnRails
>
>
>
>
<RichardDummyMailbox58...-FtJgd9dCuO3JTKoYRCtP1UEOCMrvLtNR@public.gmane.org>
wrote:
> > Hi,
>
> > I have three tables: Expenses, Vendors and Vendor _Accounts
>
> > It should operate as follows:
> > When a new Expense record is created,
> > A vendor is selected from a drop-down of Vendors and,
> > An account is selected from a drop-down of Vendor_Accounts where
> > Vendor_Accounts#vender == selected vendor
>
> > So I should have a structure something like:
> > class Expense
> >         has_one Vendor
>
> > class Vendor
> >         has_many Vendor_Accounts where Vendor#id ==
Vendor_Accounts#vendor
> >         belongs_to Expense
>
> > class Vendor_Account
> >         belongs_to Vendor
>
> > I don’t think I should have Expense, Vendor and Account tables because
> > the accounts defined by each vendor bear no relationship with the
> > other vendors’ account beyond the mere concept of “account”.
>
> > Does this make sense, and if so,  how precisely should I describe
> > these relationships? Am I close with the above idea?
>
> > BTW, I''m running Rails 2.3.5, Ruby 1.8.6, WinXP-Pro/SP3,
Firefox
> > 3.6.2, Firebug 1.5.3,
> > MySQL 5.0.37-community-nt, Mongrel, Apache HTTP Server 2.2.15
>
> > Thanks in Advance,
> > Richard
>
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