why PG::UniqueViolation: ERROR: duplicate key value violates unique constraint?

Question

I have a model Post and each time a post is created I want a new instance of Moderation to be created at the same time.

So in post.rb I use the

Answer 1

Fix pkey sequences for all database:

ActiveRecord::Base.connection.tables.each do |table_name| 
  ActiveRecord::Base.connection.reset_pk_sequence!(table_name)
end