[Rails] Re: shared primary key (using the primary key as a foreign key for has_one association)

[Alexey M.]

A relevant question that i think is appropriate for this thread: can
anybody please explain to me the purpose of primary_key type in context
of migrations:
t.primary_key :person_id
?

The migration

class CreateInstructors < ActiveRecord::Migration
  def self.up
    create_table :instructors do |t|
      t.primary_key :person_id
      t.text :presentation
...

does not work (SQLite3::SQLException: table "instructors" has more than
one primary key: ... during migration),
but

class CreateInstructors < ActiveRecord::Migration
  def self.up
    create_table :instructors, :primary_key => "person_id" do |t|
      t.primary_key :person_id
      t.text :presentation
...

and

class CreateInstructors < ActiveRecord::Migration
  def self.up
    create_table :instructors, :primary_key => "person_id" do |t|
      t.text :presentation
...

seem to have completely identical effect:-/.

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