# Very simple Date math goes randomly bonkers **URL:** \ **Category:** Rails\ **Created:** [December 8, 2008, 7:56pm UTC](https://www.ruby-forum.com/t/very-simple-date-math-goes-randomly-bonkers/155156 "2008-12-08T19:56:36Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![vanderkerkoff](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/7feea3/32.png) [@vanderkerkoff](https://www.ruby-forum.com/u/vanderkerkoff)\ **Post date:** [December 8, 2008, 7:56pm UTC](https://www.ruby-forum.com/t/very-simple-date-math-goes-randomly-bonkers/155156/1 "2008-12-08T19:56:36Z")
I have a “timesheet” in my app that simply displays the week range based on a passed in date (params[:date]). The view iterates through the Date::ABBR\_DAYNAMES and shows a link to the corresponding date. Trouble is that about 40% of the time the calculated dates go bonkers. Am I missing something? Model: # Get a date range of the week that a particular date falls in # This is broken out like mad for diagnostics def self.get\_work\_week\_date\_range(date) monday = date.monday sunday = monday - 1.day eow = date.end\_of\_week saturday = eow - 1.day ``` dates = [sunday, saturday] logger.info ``` ("\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>") logger.info("\>\>\>\>\> #{date}.monday = #{monday}") logger.info("\>\>\>\>\> #{monday}-1.day = #{sunday}") logger.info("\>\>\>\>\> #{date}.end\_of\_week = #{eow}") logger.info("\>\>\>\>\> #{eow}-1.day = #{saturday}") logger.info("\>\>\>\>\> #{date} == [#{dates[0]}, #{dates[1]}]") logger.info ("\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>\>") ``` dates ``` end Logger output: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > 2008-12-08.monday = 2008-12-08 > > > > > 2008-12-08-1.day = 2008-12-07 > > > > > 2008-12-08.end\_of\_week = 2008-12-14 > > > > > 2008-12-14-1.day = 2008-12-13 > > > > > 2008-12-08 == [2008-12-07, 2008-12-13] > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > … n times later … ---
**Author:** ![vanderkerkoff](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/7feea3/32.png) [@vanderkerkoff](https://www.ruby-forum.com/u/vanderkerkoff)\ **Post date:** [December 8, 2008, 8:16pm UTC](https://www.ruby-forum.com/t/very-simple-date-math-goes-randomly-bonkers/155156/2 "2008-12-08T20:16:05Z")
On Dec 8, 2008, at 10:55 AM, Matt D. wrote: > I have a “timesheet” in my app that simply displays the week range > based on a passed in date (params[:date]). > The view iterates through the Date::ABBR\_DAYNAMES and shows a link to > the corresponding date. What do you pass to get\_work\_week\_date\_range? Is it a string? Or an instance of Date? Or Time? If it worked once it should always work. Which suggests that maybe you’re passing in something different from time to time? One time a Date, one time a Time? Maybe? Put together a test and explicitly pass the _same_ argument (class and value) and see if you can duplicate it. ---
**Author:** ![vanderkerkoff](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/7feea3/32.png) [@vanderkerkoff](https://www.ruby-forum.com/u/vanderkerkoff)\ **Post date:** [December 8, 2008, 8:30pm UTC](https://www.ruby-forum.com/t/very-simple-date-math-goes-randomly-bonkers/155156/3 "2008-12-08T20:30:15Z")
> What do you pass to get\_work\_week\_date\_range? Is it a string? Or an > instance of Date? Or Time? I pull the date in from the params hash, and immediately parse it to a Date: Date.parse(params[:date]) rescue Date.today > If it worked once it should always work. Which suggests that maybe > you’re passing in something different from time to time? One time a > Date, one time a Time? You’re right, that’s why I’ve pounded my head against the wall for a week! This method is only called from one other method, and I’ve extracted it really only for testing. > Put together a test and explicitly pass the _same_ argument (class and > value) and see if you can duplicate it. All tests pass ☹ it “should know how to get the week based on a date” do TimeCard.get\_work\_week\_date\_range(Date.parse(“2008-08-05”)).should == [Date.parse(“2008-08-03”), Date.parse(“2008-08-09”)] TimeCard.get\_work\_week\_date\_range(Date.parse(“2008-01-01”)).should == [Date.parse(“2007-12-30”), Date.parse(“2008-01-05”)] TimeCard.get\_work\_week\_date\_range(Date.parse(“2008-02-29”)).should == [Date.parse(“2008-02-24”), Date.parse(“2008-03-01”)] TimeCard.get\_work\_week\_date\_range(Date.parse(“2007-02-28”)).should == [Date.parse(“2007-02-25”), Date.parse(“2007-03-03”)] end ---
**Author:** ![vanderkerkoff](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/7feea3/32.png) [@vanderkerkoff](https://www.ruby-forum.com/u/vanderkerkoff)\ **Post date:** [December 8, 2008, 9:41pm UTC](https://www.ruby-forum.com/t/very-simple-date-math-goes-randomly-bonkers/155156/4 "2008-12-08T21:41:32Z")
> Perhaps the key thing to note is that 1772-05-19 is about 236 years > and 7 months ago, which (get your calculators out) is about 86400, ie > the number of seconds in a day. Whereas on an instance of Time, +/- 1 > means +/- 1 second, on instances of Date/DateTime +/- means +/- 1 > second. That is I suspect the basic problem. Man, good call. > On newer versions of rails, things like 1.day are smart enough to do > the right thing whether or not you add a date or a Time to them (the + > method on Date is overriden to check if the argument is a thing like > 1.day). I’m using 2.2.2, but… > Somewhere this has gone wrong. If you have any plugins that mess with > dates (or if you’ve being doing stuff like that yourself) then I’d > have a look at those - it could be something like once some random > model is loaded some extensions to Date are pulled in at that point > and from then onwards calculations are borked. … I do monkeypatch Date, but I ensured that I wasn’t actually overriding any existing method. Thanks for you help Fred, this smells like the right track. ---
**Author:** ![vanderkerkoff](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/7feea3/32.png) [@vanderkerkoff](https://www.ruby-forum.com/u/vanderkerkoff)\ **Post date:** [December 8, 2008, 11:05pm UTC](https://www.ruby-forum.com/t/very-simple-date-math-goes-randomly-bonkers/155156/5 "2008-12-08T23:05:06Z")
It was the facets/time library. It was loaded in a totally separate part of the app, in a method that had not much to do with anything. Thanks again Frederick; that one got your a WWR recommendation 😉 ---
**Author:** ![vanderkerkoff](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/7feea3/32.png) [@vanderkerkoff](https://www.ruby-forum.com/u/vanderkerkoff)\ **Post date:** [December 8, 2008, 9:15pm UTC](https://www.ruby-forum.com/t/very-simple-date-math-goes-randomly-bonkers/155156/6 "2008-12-08T21:15:06Z")
On Dec 8, 6:55 pm, Matt D. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > > > > 2008-12-08.monday = 2008-12-08 > > > > > > 2008-12-08-1.day = 1772-05-19 > > > > > > 2008-12-08.end\_of\_week = 3428-04-08 > > > > > > 3428-04-08-1.day = 3191-09-18 > > > > > > 2008-12-08 == [1772-05-19, 3191-09-18] Perhaps the key thing to note is that 1772-05-19 is about 236 years and 7 months ago, which (get your calculators out) is about 86400, ie the number of seconds in a day. Whereas on an instance of Time, +/- 1 means +/- 1 second, on instances of Date/DateTime +/- means +/- 1 second. That is I suspect the basic problem. On newer versions of rails, things like 1.day are smart enough to do the right thing whether or not you add a date or a Time to them (the + method on Date is overriden to check if the argument is a thing like 1.day). Somewhere this has gone wrong. If you have any plugins that mess with dates (or if you’ve being doing stuff like that yourself) then I’d have a look at those - it could be something like once some random model is loaded some extensions to Date are pulled in at that point and from then onwards calculations are borked. Fred