Re: [Rails] Re: How to implement custom row ordering

On 16 May 2010 06:21, Albus Dumbledore <lists@ruby-forum.com> wrote:
> Well. I am having trouble understanding how acts_as_list works. I do not
> quite comprehend what the table schema for the example given by DHH must
> be:
>
> [code]
>
>  class TodoList < ActiveRecord::Base
>    has_many :todo_items, :order => "position"
>  end
>
>  class TodoItem < ActiveRecord::Base
>    belongs_to :todo_list
>    acts_as_list :scope => :todo_list
>  end
>
> [/code]
>
> More precisely I wonder where should the `position` column go? To me it
> looks like it should go with the table having the foreign keys, i.e.
> `todo_items` table. Then it would seem that there would be no need for a
> `todo_lists` table, right? So it would be all about the todo_items
> table.

Yes; the position column goes on the table you want ordered.
The purpose of the todo_list table is to allow there to be more than
one list of items (if you want one). The "scope" field is a way of
identifying what separates the lists in the items table.

So if every user needs a list, then you can scope by user; if you're
only having one list of the items, then there's no need for a scope -
just position.

>  It's scope that is bothering me. Firstly we can have our rows grouped
> by a foreign key (which seems trivial enough). However, what happens if
> it is a polymorphic reference, i.e. we need to use two columns to select
> a unique row?

Right.... your posting is suffering a little "feature creep" at the
moment. If you post what the limits are of the real problem you have,
then people can suggest solutions. If you have a complicated data
structure, then post some of the model code so we can all get our
heads around it.

>
> Thank you!
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