问题
All the tables in the database created by a rails application seem to have created_at and updated_at columns. What creates these? Are they optional, or does something internal rely on them?
回答1:
They are created by default when you run the ActiveRecord migration for a model. ActiveRecord automatically populates/updates them when you create or update a model instance (and thus the underlying database table row) respectively.
You can remove the columns by removing the t.timestamps line from within the model migration file.
- Ruby on Rails Guides: Migrations
回答2:
In your database migration for every table you have something like t.timestamps. Erase this and your database columns created_at and updated_at won't be created
回答3:
Adding to what Octopus said, they are optional and are used to track the record creation and updating date time in the corresponding tables.
来源：https://stackoverflow.com/questions/4722785/where-do-the-created-at-and-updated-at-columns-come-from