Ruby on Rails

I have the task to work with a database that I am not allows to modify. It is a legacy database.

In my class I have put some sample data to illustrate what I am trying to do. I working with rails 4 and ruby 2.

Can someone please tell me how am I supposed to code this association. There are no field_id in any of the tables.

Thank you very much in advance!

class Midatum < ActiveRecord::Base   # ...,|diagn1 |diagn2 |diagn3   # ----+-------+-------+------   #  ...| "0123"| nil   |"0124"   #  ...| "0123"| nil   |"0124"   #  ...| "0123"| "1123"| nil

     belongs_to :icd9, :foreing_key => :diagn1   belongs_to :icd9, :foreing_key => :diagn2   belongs_to :icd9, :foreing_key => :diagn3  end    class icd9 < ActiveRecord::Base   # icd9  |description    # ------+------------   #"0123" |"some text"   #"0124" |"some other text"   #"1123" |"description text"   #"1133" |"description text"

 has_many :midata, :foreing_key => :icd9, :primary_key => :icd9  end