created_at 和 updated_at 列从何而来？

Question

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?

Answer 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

Answer 2

In your database migration for every table you have something like t.timestamps . Remove this from your migration and your database columns created_at and updated_at won't be created.

Edit:

In case you need to create a new migration to remove those columns you can use remove_timestamps or remove_column

remove_timestamps definition shows how you can use remove_column if you want to.

def remove_timestamps(table_name, **options)
  remove_column table_name, :updated_at
  remove_column table_name, :created_at
end

Answer 3

补充八达通所说的，它们是可选的，用于跟踪相应表中的记录创建和更新日期时间。