How do I show grouped rows from model? - ruby-on-rails

Question

I have a model:
class Row < ActiveRecord::Base
belongs_to :description
attr_accesible :id, :q_id, :quantity, description_id
end
class Description < ActiveRecord::Base
has_many :rows
translate :description #globalize3, ignore it.
attr_accesible :id, :other
end
In this case, Description and Row have a 1:N relationship (N from 1 to 3).
What is the best way to show this in table format in Haml? For example if we have in the DB:
Row:
1 | 1 | 20 | 1
2 | 2 | 22 | 1
3 | 1 | 30 | 2
4 | 3 | 31 | 2
5 | 2 | 32 | 2
Description:
1 | asd
2 | zxc
I would like to show this form:
desc | q1 | q2 | q3 |
-----+----+----+----+
asd | 20 | 22 | -- |
zxc | 30 | 32 | 31 |
UPDATE
I added a new attribute (q_id) that indicates the "q" position (1, 2, or 3) to my Row model.

Answer 1

In your controller code:
#descriptions = Description.eager_load(:rows).order('descriptions.id, rows.q_id')
In your view:
%table
%tr
%th= 'desc'
%th= 'q1'
%th= 'q2'
%th= 'q3'
- #descriptions.each do |description|
%tr
%td= description.description
- (0..2).each do |i|
%td= description.rows[i].try(:quantity) || '--'
UPDATE
If you want to limit the rows to a specific user association, you can do so like this:
#descriptions = Description.eager_load(:rows).
where(rows: {user_id: some_user.id}).
order('descriptions.id, rows.q_id')
If you are concerned that this may exclude a description that has no matching rows, you can substitute a SQL fragment with a NULL alternative:
#descriptions = Description.eager_load(:rows).
where('rows.user_id = ? OR rows.id IS NULL', some_user.id).
order('descriptions.id, rows.q_id')

Answer 2

Something like:
%table
%tr
- Description.includes(:rows).find_each do |description|
%td= description.description
%td= format_quantity description.rows.first
%td= format_quantity description.rows.second
%td= format_quantity description.rows.third
And a helper function
def format_quantity(row)
row.present? ? row.quantity : '--'
end
UPDATE
For the order of rows, you could specify that on your relation
class Description < ActiveRecord::Base
has_many :rows, order: 'q_id'