问题
In my database migration file I inserted the line:
t.timestamps
Two columns, as I expected, were created: "updated_at" and "created_at". However, their type is "datetime" and not "timestamp".
I am using MySQL and the "timestamp" type, as I understand, is designed exactly for such cases, as it uses less space and is independent of timezone.
So, is there any reason, why Rails 3 uses "datetime" and not "timestamp"? Should I try to fix that? If yes, is there any way to do this besides not using "t.timestamps" and defining "updated_at" and "created_at" columns separately every time for each new table?
回答1:
From memory, the mysql timestamp column type behaves similar to updated_at in that it is updated with the current time whenever the record is updated.
While this is useful for the updated_at column, this is not the desired behaviour for created_at.
In addition, Rails handles the timezone as specified in your app's settings (should would normally be set to UTC), so using mysql's time may be inconsistent with other datetime records.
回答2:
timestamp columns have a limited range which begins in 1970 and ends in 2038. You can google "Unix Millennium Bug" for more information, but it's basically because unix timestamps are stored as a 32-bit signed integer. A timestamp is expressed in seconds since Jan. 1, 1970, and the number wraps on itself in 2038. For this reason, I typically use datetime even when timestamp seems like an easier solution, especially to represent historical or forecasted data further off into the past or future.
来源：https://stackoverflow.com/questions/5053897/ruby-on-rails-why-activerecord-uses-datetime-type-instead-of-timestamp-for