ActiveRecord model without primary key

Question

I have a ActiveRecord model GPA that doesn't have a primary key:

class GPA < ActiveRecord::Base

end

When I try to call GPA.first.to_json I get TypeError: false is not a symbol. I'm guessing that this is due to ActiveRecord trying to lookup the primary key. What is the correct way to implement a model without a primary key?

Answer 1

Normally there is either some column or combination of columns which together do form a primary key. When you say your table doesn't have a primary key do you mean it doesn't have an id field?

Is there another column that is a unique/natural key? If so you can do:

class GPA < ActiveRecord::Base
  set_primary_key :strm    # eg column strm is a unique/natural key
end

You can also use composite keys with the composite keys gem, as follows:

class GPA < ActiveRecord::Base
  set_primary_keys :student_id, :strm
end

Answer 2

Add a migration that adds id as a column. It's not going to hurt any existing code. Just make sure it's got an autoincrement on it so it's not going to moan about duplicate entry 0.