Hello! I'm looking for assistance EXTENDING an example from the Agile
Web Development With Rails book: Composing Data with Aggregation (page
324).
I'm trying to map three columns to a single Ruby object. However,
unlike the example in the Agile Web Development book, the three
columns I want to map into one object come from THREE DIFFERENT
models.
I want to map the following three columns into one object:
grade.grade_abbr, strand.strand_abbr, standard.number (ex. 5 NS 2.3).
Also, I only need to read the new object--not edit the original
columns.
Here are the models and their relationships:
class Standard
belongs_to :strand
belongs_to :grade
class Strand
has_many :standards
class Grade
has_many :standards
When I originally setup my Standard table with grade_abbr and
strand_abbr, it easy to follow the example in the Agile Web
Development because each column was contained within the Standard
model. However, I had to move Grade and Strand into their own tables,
so the Standard table contains grade_id and strand_id--not the actual
objects themselves.
When I played with the example from the Agile Web Development book, I
couldn't get :grade.grade_abbr and strand.strand_abbr to work. The
code below was the best that I could come up with but it shows
grade_id and strand_id. Does anyone have a suggestion for how to make
this work or for a new strategy?
class Standard < ActiveRecord::Base
composed_of :full_standard,
:mapping =>
[
%w[grade_id grade_id],
%w[strand_id strand_id]
%w[number number]
]
class FullStandard < ActiveRecord::Base
attr_reader :grade_id, :strand_id, :number
def initialize(grade_id, strand, number)
@grade_id = grade_id
@strand_id = strand_id
@number = number
end
def to_s
[ @grade_id, @strand_id, @number ].compact.join(" ")
end
end
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