Ruby on Rails: why ActiveRecord uses "datetime" type instead of "timestamp" for timestamp fields?

Question

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?

Answer 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.