Question

I would like to modify updated_at attribute so that every time record is updated it would only show date and hours while hours and minutes being zeros. Instead of 2010-08-13 11:04:12, there would be 2010-08-13 11:00:00. What is the most rational way to do this in Rails 2.3?

Update

The reason why I want to do what I have asked is because I would like to sort data, by date with hours and seconds omitted.

Thanks!

Answer 1

Don’t try to change the value stored in the database; change how you are outputting it:

timestamp = @model.updated_at # where @model is your model object

# output it in a format that overrides the values for minute and second
puts timestamp.strftime "%Y-%m-%d %H:00:00"

See the strftime ruby doc for other format specifiers you can use.

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Based on your update, I would still not change how updated_at is stored, but instead format the date within the ORDER BY of your query. For instance, you could

ORDER BY DATE(updated_at), HOUR(updated_at), ...

I did a very quick profiling test on a live table in my application, which has about 22,000 records. ORDER BY updated_at took between 2.94 and 3.19s to complete, with a mean time of 3.00s. ORDER BY DATE(updated_at), HOUR(updated_at) took between 2.93 and 3.06s to complete, with a mean time of 2.99s. Here’s the profiling data:

+----------+------------+-----------------------------------------------------------------+
| Query_ID | Duration   | Query                                                           |
+----------+------------+-----------------------------------------------------------------+
|        1 | 2.94530500 | SELECT * FROM posts ORDER BY updated_at                         |
|        2 | 2.94583800 | SELECT * FROM posts ORDER BY updated_at                         |
|        3 | 3.18711700 | SELECT * FROM posts ORDER BY updated_at                         |
|        4 | 2.96923700 | SELECT * FROM posts ORDER BY updated_at                         |
|        5 | 2.97255400 | SELECT * FROM posts ORDER BY updated_at                         |
|        6 | 3.06706800 | SELECT * FROM posts ORDER BY DATE(updated_at), HOUR(updated_at) |
|        7 | 3.00414400 | SELECT * FROM posts ORDER BY DATE(updated_at), HOUR(updated_at) |
|        8 | 2.95551500 | SELECT * FROM posts ORDER BY DATE(updated_at), HOUR(updated_at) |
|        9 | 3.02181900 | SELECT * FROM posts ORDER BY DATE(updated_at), HOUR(updated_at) |
|       10 | 2.93130000 | SELECT * FROM posts ORDER BY DATE(updated_at), HOUR(updated_at) |
+----------+------------+-----------------------------------------------------------------+