fix_PG::ForeignKeyViolation.rb

class Device
  belongs_to :car
end

class Car
  has_one :device
end

# Rails adds foreign key constraints automatically, so sometimes (not sure when exactly),
# when you try to +destroy+ a Car, it will complain with a PG::ForeignKeyViolation: ERROR: ...
# We need to add a on_delete option from the database itself.

remove_foreign_key :devices, :cars
add_foreign_key :devices, :cars, on_delete: :nullify # Options are :nullify, :cascade and :restrict