Mrelation does not exists

Hello!

I'm having the following error:

RuntimeError: ERROR C42P01 Mrelation "subjects_users_id_seq" does not exist Fnamespace.c L200 RRangeVarGetRelid: SELECT currval('subjects_users_id_seq')

when I try to do:

subject= SubjectsUser.new(params[:subjects_user])
subject.save

The models:

class User < ActiveRecord::Base
  has_one :last_entrie
  has_one :address_book
  has_and_belongs_to_many :subjects
  has_one :user_detail
  has_and_belongs_to_many :subjects
end

class Subject < ActiveRecord::Base
  has_and_belongs_to_many :users
  belongs_to :subject_group
end

class SubjectsUser < ActiveRecord::Base
end

Thank you for your attention,

Paulo Abreu

You're using postgresql.

It uses a 'serial' field for each primary key. When it inserts a new
row, it pulls the next 'id' value from something called a sequence (basically,
a counter).

For some reason, the subjects_users_id_seq sequence isn't there
any more.

You can recreate it - try '\h create sequence' from inside psql.
If you have existing data in subjects_users, you need to make sure
the sequence starts with a number 1 higher than the current highest value
in the 'id' field of subjects_users.