I'm working on a project with a rails api and an iOS client, using the updated_at field as the reference to detect modifications on the server that happened after the last pull from the client.
The updated_at datetime has a precision in milliseconds, meaning that
Model.updated_at.to_f
returns something like "1368977381.063427". This is sent to the client formatted as "2013-05-19T15:29:41.063427000Z".
The trouble is, when I get that datetime back from the client, parse it and query with it, the milliseconds are lost.
last_update = DateTime.strptime("2013-05-19T15:29:41.063427000Z", "%Y-%m-%dT%H:%M:%S.%N%z")
Model.where("updated_at > ?", last_update)
is as good as doing
last_update = DateTime.strptime("2013-05-19T15:29:41Z", "%Y-%m-%dT%H:%M:%S%z")
Model.where("updated_at > ?", last_update)
As a result, I always get at least one result when I should get none, because the milliseconds are truncated.
How can I take those into account in my query ?
Try
Model.where("updated_at > ?", last_update.strftime("%Y-%m-%dT%H:%M:%S.%N%z"))
You can also set this format as the standard format for DateTime in databases by setting (i.e. in an initiallizer):
Time::DATE_FORMATS[:db]= '%Y-%m-%dT%H:%M:%S.%N%z'
then your original query works again:
Model.where("updated_at > ?", last_update)
See the Rails API for DateTime.to_s
(aka .to_formated_s)
If you're using the ISO8601 standard you can use .iso8601(10)
. Don't know why but it rounds to seconds by default.
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