I am making a world clock QML program. I am currently using an API to get the timezone ID of a certain city.
So for instance, for Delft, it would return
TimezoneID = Europe/Amsterdam
I store the city name and its timezoneID in a local sql database so that I wouldn't have to keep parsing online for the timezone info.
In my application, I have a ListView which displays the cityname along side its local time. How do I calculate the time at Delft using my system time and its timezoneID?
As far as I know, QML itself does not have this functionality, here are alternatives:
Since you already use a database, why don't you simply add the zone.tab part of the tz database to your database and calculate the times yourself? (Don't forget about daylight saving time...)
If you don't like that, you can also use TimezoneJS, a javascript library for handling timezones (which needs a copy of the same database mentioned above).
Or you write a C++ plugin for QML that encapsulatesdate and tzset.
Related
Is there any way to query a SQLite database for basic meta data such as:
Last date/time updated
Hash of database to indicate "state"
I am just looking for a simple, infrastructural way to have a script evaluate different databases and take a reasonable point of view on whether they are the same "state" as other databases in a different environment (PROD and DEV for instance).
In my experience, if no update, new record, or any change is made to the SQLite database file, the last modified time of the file doesn't change. So the last modified time should suffice for the time of any change made to database.
If 2 database files with same state are only accessed for reading, their modified times are always the same.
Similarly you get the file sizes for comparison.
You can use the whole file to calculate hash. If you consider same data in the database as the same "state" regardless of any difference in the past, then maybe you want hash of the all records in database, which is probably not simple.
I have an existing web application with 70+ projects; DB: 700+ tables, 500+ stored procedures.
Currently there are many tables with Datetime/Date fields.
When saving date/datetime information in DB, i need to change them to UTC to support multiple time zone (since the application is going to be accessed across many regions - servers can also be hosted on multiple regions; currently it is accessed only from one region)
In order to do this i have come up with the below steps:
Get the list of tables with date/datetime field.
Check how its date time field is populated (ie. either through the application or through the procedure)
List item.
convert the datetime to UTC before saving it to DB.
When displaying it in the user's browser, convert the time back to the user's timezone.
Can write a query to update existing values with UTC.
The problem is the application by itself is very huge and there are too many places (both from the application & procedure) where datetime is updated; Though i can get the list of tables/procedure names through query directly, updating each procedure (in back end) /file (in front end) is a very tedious process
I would like to know the best approach/suggestions (change the application to support multiple timezone with minimal changes) to proceed in this situation.
Thanks!
The ideal situation is that all dates are UTC, in the stored procedures, in process code, in API interfaces etc.
The only time it should not be UTC is directly before it is rendered for a human user
As you indicate a web application, this should be isolatable to just the HTML rendering areas, and this should be the only code you need to change after you switch the DB to UTC
You should just need two function changes:
Decode human input into a valid date and convert into UTC from that sessions time zone (do this before any other processing logic)
Convert date value from UTC to current sessions time zone, and format into human readable form (do this just before displaying date)
These two functions should already exist in your UI code for date formatting and validation, they just need tweeking
It's too late for you, but when designing an application which puts a datestamp on any record changes, the correct thing to do is to write a SQL trigger that sets the date appropriately.
We have an ASP.NET website and an SQL database hosted in US. Whenever I use the function Now() in VB.NET and getdate() in SQL, I get the US' current time. The problem is, the client is in the Philippines which is on GMT+8 Time Zone. My question is, is there any way I can set the Time Zone of a specific database and website so that when I use the functions, I'll get the Philippine's current time? How do you deal with this? As much as possible, we don't want to do subtraction or addition to the result date of the functions since in the future, clients will be from other country. It will give us headache updating the codes if we do that.
Thank you in advance!
Given that your clients may be in different time zones, you should store a timezone for the clients, that they (or you) can set as a preference for their account. Store all dates+times as UTC, and then convert to their timezone when displaying results in your interface.
This question has already been addressed to a great extent in the following question:
How to work with time zones in ASP.NET?
Follow-up:
Unfortunately, the SQL server date is a system-level setting, so it's not really something that can be manipulated on a per-session basis. It sounds like you will need to make some code changes, but you can isolate them.
Do you have a session-level variable which contains the client time zone offset? If not, create one.
Create a small date/time utility class.
In the utility class, provide 3 methods to:
(1) get the current date/time (offset to the client's time zone)
(2) pass in a database date/time to return the time offset for the client's TZ.
(3) pass in a time from the client to subtract out the client's TZ difference.
You will have to make code changes, but you can probably use those utility functions to wrap inputs and outputs everywhere, centralizing the logic. Microsoft has a page about mis-steps to avoid when using the DateTime class and manipulating time zones:
http://msdn.microsoft.com/en-us/library/ms973825.aspx#datetime_topic1a
I have an application where all the DateTime's are always the time of the server. That means one time zone. The idea is to make the application compatible all over the world. The first step is to convert all the stored DateTime's in the database to UTC, that's no problem. Second step is to assume a timezone for the user (based out business logic), and to use as a default for displaying and parsing user input. Furthermore it would be nice if methods like DateTime.Now and other method calls that construct datetimes without explicit time zone/region information would also assume this time zone/region.
The idea is to assume a time zone for a user from the database. I have the user and his time zone, thats's no problem.
The problem is the presentation logic. There are DateTime.now methods all over the code, to convert all these methods is a lot of work.
To avoid that I need a global time zone setting where the DateTime knows which time zone it is. Preferably on a generic place.
class business logic
InitializeCulture()
set time zone for user
end function
end class
class presentation logic
sample()
TimeOfTheCurrentUser = DateTime.now
end function
end class
If you are looking for best practice for time zone handling in (more or less) enterprise application, I can share the proven one:
Store all date and time related information in UTC. Storing it as local time (on server or wherever else) always brings a risk that somebody, somewhere, someday forget to convert them and the results would be less than ideal. Of course it means that dates and times should be instantiated via DateTime.UtcNow or with proper DateTimeKind selected (this refers to parsing as well).
Obviously you need to convert time zone before displaying DateTime to end user. And you surely realize that you need to obtain this information from some source (thus the question). That somewhere could be client-side (which would work especially well with thick client and not so well with thin client's JavaScript) but could be just as well the user profile. If your application has user profiles, I would definitely recommend to allow user to select preferred time zone. Other g11n-related settings would be preferred culture for e-mails or preferred language. All of these settings should be detected and preselected (so the user does not have to think or more importantly click too much).
To convert DateTime classes to local time in another time zone, you would use TimeZoneInfo class. There are several ways to do that...
If you would implement this method, you may hit the problem with time zone names - they are in server's culture, so you would need to externalize (move to resource file) what TimeZoneInfo's DisplayName shows you and let translators do their jobs.
Also just a quick word what I meant by detect time zone.
On thick client you would do that by simply reading local time zone:
TimeZoneInfo currentTimeZone = TimeZoneInfo.Local;
With JavaScript (thin client) it is not that easy. The only thing you can get is a time zone offset (which could vary depending on date & time) on given date:
var date = new Date();
var offset = date.getTimezoneOffset(); // GMT offset in minutes
I am working on cleaning up a bug in a large code base where no one was paying attention to local time vs. UTC time.
What we want is a way of globally ignoring time zone information on DateTime objects sent to and from our ASP.NET web services. I've got a solution for retrieve operations. Data is only returned in datasets, and I can look for DateTime columns and set the DateTimeMode to Unspecified. That solves my problem for all data passed back and forth inside a data set.
However DateTime objects are also often passed directly as parameters to the web methods. I'd like to strip off any incoming time zone information. Rather than searching through our client code and using DateTime.SpecifyKind(..) to set all DateTime vars to Undefined, I'd like to do some sort of global ASP.NET override to monitor incoming parameters and strip out the time zone information.
Is such a thing possible? Or is there another easier way to do what I want to do?
Just to reiterate -- I don't care about time zones, everyone is in the same time zone. But a couple of users have machines badly configured, wrong time zones, etc. So when they send in July 1, 2008, I'm getting June 30, 2008 22:00:00 on the server side where it's automatically converting it from their local time to the server's local time.
Update: One other possibility would be if it were possible to make a change on the client side .NET code to alter the way DateTime objects with Kind 'Undefined' are serialized.
I have dealt with this often in many applications, services, and on different platforms (.NET, Java, etc.). Please believe me that you do NOT want the long term consequences of pretending that you don't care about the time zone. After chasing lots of errors that are enormously difficult and expensive to fix, you will wish you had cared.
So, rather than stripping the time zone, you should either capture the correct time zone or force a specific time zone. If you reasonably can, get the various data sources fixed to provide a correct time zone. If they are out of your control, then force them either to the server's local time zone or to UTC.
The general industry convention is to force everything to UTC, and to set all production hardware clocks to UTC (that means servers, network devices like routers, etc.). Then you should translate to/from the user's local time zone in the UI.
If you fix it correctly now, it can be easy and cheap. If you intentionally break it further because you think that will be cheaper, then you will have no excuses later when you have to untangle the awful mess.
Note that this is similar to the common issue with Strings: there is not such thing as plain text (a String devoid of a character encoding) and there is no such thing as a plain (no time zone) time/date. Pretending otherwise is the source of much pain and heartache, and embarrassing errors.
OK, I do have a workaround for this, which depends on the fact that I only actually need the Date portion of the DateTime. I attach this property to every Date or DateTime parameter in the system
<XmlElement(DataType:="date")>
This changes the generated wsdl to have the type s:date instead of s:dateTime. (Note that simply having the type of the .NET method parameter be a Date rather than a DateTime did NOT accomplish this). So the client now only sends the date portion of the DateTime, no time info, no time zone info.
If I ever need to send a Date and Time value to the server, I'll have to use some other workaround, like making it a string parameter.
I've had issues with the time zone information as well. The problem is I'm already providing the datetime fields in UTC. Then the serialization occurs and the local offset becomes part of the date/time. The dates/times for our vendor in a different timezone were pretty messed up. I got around this problem by using the tsql convert function on the datetime fields in my select statement I used to populate my datasets. This converted the fields to a string variable, which translates nicely to a datetime value automatically on the client side. If you just want to pass the date, you can use the 101 code to provide just the date. I used 126 to provide the date and time exactly how it appears in my database columns, with the timezone information stripped out.