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Very simply put, I have a query:

@current_user.items.where('updated_at > ? AND updated_at < ?', last_sync_time_from_client, current_time)

My problem is, I think the time being compared in the database and the last_sync_time_from_client are being compared on a float basis. This always results in the updated_at > last_sync_time_from_client being true even when the time is identical to the second.

I.e.

(db item)updated_at.to_f # 1541246811.022979
last_sync_time.to_f # 1541246811.0

This means that the times, which are the same down to the second, will return oddities. Is there a way to fix this, or should I simply add a second to the last_sync_time_from_client to account for Rails being strange here?

JapanRob
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    Nothing is strange here. Seconds are not the smallest unit of time. You can [truncate the date to the second](https://stackoverflow.com/a/10213289/2697183) if your logic dictates that, but I don't see why you should. Don't you want to return the items that were updated 1 millisecond after the `last_sync_time_from_client`? Do you also expect the `updated_at` to be in the future? If not, then ensuring that it is less than current_time is not necessary – AbM Nov 03 '18 at 13:46

1 Answers1

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Here are three solutions. Solution 1 is the best (non-destructive). Solutions 2 and 3 affect the stored values in database directly, and so choose it at your own risk.

Solution 1

Use 

date_trunc('second', updated_at);

instead of updated_at. See the answer to "Discard millisecond part from timestamp" for detail.

Solution 2

Force Rails always to update the timestamp with the precision of a second, truncating the sub-second part to zero.

See an answer to "Is there a way to change Rails default timestamps to Y-m-d H:i:s (instead of Y-m-d H:i:s.u) or have laravel ignore decimal portion of Y-m-d H:i:s.u?"

Solution 3

Make the precision of the updated_at column in the database a second, as opposed to the default sub-second (like a milli-second).

See the answers to "how to change rails migration t.timestamps to use timestamp(0) without timezone in postgres" for how to do it with Rails migration.

Masa Sakano
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    Thank you. I realized that there was a problem with my own code - I should have been keeping the milliseconds in the first place, but I accepted this answer because it's really informative. – JapanRob Nov 05 '18 at 00:54