I'm trying to have a record with ends\_at column which is suppose to have the created\_at value with 5 minutes added to it for instance:

```
Class Post < ApplicationRecord
  after_create :set_end_time

  private
    def set_end_time
      self.ends_at = self.created_at + 5.minutes
    end
end

```

this saves the ends\_at column as a null in the database