Relating two models through associated foreign keys with ruby on rails -

i'm having trouble setting relationships , queries. here simple explaination of want accomplish. have 3 models: drawings, changes, , revisions.

a drawing has many revisions

a change has many revisions

a change has many drawings through revisions

the drawings have fields primary key string: drawing_number unique each drawing.

when create new change, have nested form creates new revisions within change. have 1 of fields in new revision drawing_number though foreign key drawing_id. there way set enter drawing_number in form, finds drawing_id matches drawing_number, , adds drawing_id drawing_id column in revisions table.

in other words, want relate revisions drawings using associated field not foreign key.

for example: have drawing_id = 7 , drawing_number = a7114b1

i create new change has revision form nested in it. enter drawing_number a7114b1 form, revision model has drawing_id column, not drawing_number column. logic find drawing_id matches drawing_number, , place drawing_id revisions table.

assuming drawing_number == drawing_id

if understood well, data correctly modeled, want alias attribute name on drawing. can done #alias_attribute:

class drawing < activerecord::base   alias_attribute :drawing_number, :drawing_id end 

now can use drawing_number attribute way drawing_id, like:

> drawing.where(drawing_id: 1) == drawing.where(drawing_number: 1)  => true 

assuming drawing_number != drawing_id

i'm assuming drawing have attribute number , revision have attribute drawing_number, both strings. need manually set foreign_key , primary_key of associations, following:

class drawing < activerecord::base   has_many :revisions, foreign_key: :drawing_number, primary_key: :number end  cass change < activerecord::base   has_many :revisions end  class revision < activerecord::base   belongs_to :drawing, foreign_key: :drawing_number   belongs_to :change end