So in my PHP code, I do timezone selection for the user, where I have a table of timezones and their hour-shift values from GMT. I then use that to add to the DATETIME column values whenever the user picks his timezone in the SETTINGS.
So I have two functionalities: reading from DATETIME column in the database, and WRITING to the DATETIME column. Obviously, the first one I need to "add" the timezone difference before showing it to the user (using DATEADD() in SQL), while the second I need to "subtract" the timezone difference before store it in the database (also using DATEADD()). That way, all my stored timezones are in GMT, and viewed based on the selection of timezone of the user.
However, the Daylight Saving is the problem. What approach should I do (whether on SQL level OR PHP level), to solve this problem? Is using DATEADD() in SQL enough to take care of DAYLIGHT Savings? I have no clue. Please help!
With SQL 2008 you have the new data time DATETIMEOFFSET which has time zone awareness as offset (as opposed to as timezone name). With this datatype you can get the UTC time of any value and then you can render it properly according to the user timezone (which is a transformation that belongs in the PHP code). The other option is to just store UTC always, in the old DATETIME data type. Whatever you do, the translation from user local to UTC and from UTC to user local belongs on the rendering in PHP, not to the SQL so DATEADD has not place in this code. The PHP DateTime has timezone support which is daylight savings aware.
GMT does not have daylight savings, so all your stored times should not have daylight savings within them. Before you store, and on retrieval you should also calculate the daylight savings. Only some areas of the world use it.
So in answer to your question no DATEADD() isn't good enough. If you're already finding out where they are, have another table or something to look up if that timezone does daylight savings. But even within some zones some areas have daylight savings and others don't.
Related
I'm working on a PHP(CodeIgniter)/MySQL application that allows users select when their blog post will be published. How I have designed it to work so far is as below:
User sets the timezone in his/her profile.
User sets the publish date of the blog post. This date/time is assumed to be based on user's timezone.
Based on user's timezone, the publish date is converted to UTC (00:00).
The converted date is stored as DATETIME in mysql.
Server frequently converts the stored DATETIME values to server timezone and publishes the content when their time has come.
I was wondering if there is a better way to handle this situation, considering that my DB server and web server are on different machines on the cloud and might change location as well.
Since you are talking about scheduling of future time, storing only UTC isn't necessarily the best approach.
Keep in mind that time zone rules can (and do) change. If you apply an update to your time zone data (in PHP, it's done with PECL's timezonedb package), then any data you already converted to UTC might be invalid.
The better solution is to store multiple values:
The original local date and time
The original time zone (ex. "America/New_York")
The UTC date and time, converted from the local values
When you want to see if it's time to run the task, you'd compare the current UTC date and time against the stored UTC value.
When you apply time zone updates, you throw out the previous converted UTC values for all future entries, and recalculate new ones based on the updated data.
If you don't do this, then you're losing the intent that the user originally provided. And if you don't keep your time zone data updated, then your system won't be aware of various changes happening around the world, such as the changes made in Egypt earlier this year, or the changes coming in October for Russia.
Last point - If implemented properly, the time zone of your server should not matter. Compare UTC to UTC.
I need to store client timezones and am wondering if I need to take DST into consideration. All I care about is displaying the user's local timezone and if DST is in effect, then the system should reflect it.
Is it enough to set the user's timezone using date_default_timezone_set and assume that DST will be automatically calculated if there is one for that area?
Is there anything else that I need to do to safeguard that the user be shown the correct time?
EDIT:
Some great answers here, thanks.
If I store the users timestamps in UTC, regardless of their actual timezone and I use date_default_timezone_set to convert the UNIX timestamp, will the correct time be displayed if there is a DST present?
It is probably best to store dates and times as the UTC+0. When you print out dates to the user in PHP, functions like date() accept a timestamp argument. These functions also automatically converts the timestamp to the current timezone. Timestamps are always UTC+0.
In a PHP script, you can change the default timezone like this:
date_default_timezone_set("Europe/Oslo");
After that, I get this result while running date("r"):
Sun, 27 Oct 2013 11:22:52 +0100
When you use geographic timezone names, times will be converted to the correct timezone depending on which time of year it is. In my example, "CET(GMT+1)" is chosen now, but yesterday it would have given me the daylight savings timezone "CEST(GMT+2)".
To store the current time in for instance a database, you can usually just store timestamps as integers (INT(11)). The current UTC+0 timestamp is in PHP retrieved with time().
I am currently studying the best way to handle timezones on my website. People from many different countries will access it simultaneously, and I have to show them time-based information, so I thought:
Store every time on database according to my server (same timezone, defined by PHP)
Then, the user has the option to choose his timezone, and I do the needed conversions by using mysql function DATEADD.
This seems to work fine, but my questions are:
Is this the best way?
Is DATEADD the most efficient function to handle the hour difference?
Thanks.
As described in MySQL Server Time Zone Support:
The current session time zone setting affects display and storage of time values that are zone-sensitive. This includes the values displayed by functions such as NOW() or CURTIME(), and values stored in and retrieved from TIMESTAMP columns. Values for TIMESTAMP columns are converted from the current time zone to UTC for storage, and from UTC to the current time zone for retrieval.
Therefore, if you use TIMESTAMP type columns, MySQL will handle timezone conversion for you automatically: just set the appropriate timezone for the session in its time_zone variable.
You are thinking in the right direction.
I would not use the server's timezone. Instead, use Coordinated Universal Time (UTC) time. It is the World Time Standard. This is pretty much the same as Greenwich Mean Time (GMT). Note that UTC does not change with Daylight Savings Time.
TO use in PHP see: http://php.net/manual/en/function.gmdate.php
From here, you can either add hours via: http://www.php.net/manual/en/datetime.add.php
Or set the timezone based on the users preference: http://www.php.net/manual/en/datetime.settimezone.php
The one you use is based on how you get the user's timezone. If you ask them for it (most accurate) you can set the timezone in PHP with the user selecting from a combo box. If you get it from the header with JavaScript using getTimezoneOffset(); then it is best to add hours based on the timezone offset.
I personally set all the times in my DB according to the GMT +0.00 timezone. So I use UTC_TIMESTAMP() (or UTC_DATE(),UTC_TIME() - whichever applies) when I want to add the current time, for example. This is server independent so I'm confident that even if I change my server I will not need to worry about this issue in the future.
Then the options are, if your visitors have a chance to pick their own timezones, you can use the DATE_ADD() and DATE_SUB() functions to format the result before providing results.
Otherwise if you have the chance (this is my favorite solution) you can use Javascript to format that date/time, which you can make it handle easily by something like
function getLocalDate(dt) {
var d = new Date(0);
d.setUTCSeconds(dt);
return d.toLocaleDateString();
// or in some format that you choose
}
which gets the date echoed by PHP using strtotime($row['some_date']);.
I have gone through many timezone/PHP posts, and most suggest storing your datetime fields in UTC, then using the application users timezone offset when storing and displaying datetime information.
The problem i have I've inherited an application that wasn't timezone aware, and now I need to cater for this.
The server is already set to "EST +11:00 Australia/Melbourne", and there are already applications running from that server. So i can't change this.
Fortunately, I do know a users timezone offset, ie -05:00, etc,.
The application takes Javascript Dates and parses them using PHP's strtotime() function and stores in a MySQL database, like this:
$event_starts = date('Y-m-d H:i:s',
strtotime('Thu Dec 02 2010 11:15:00 GMT+1100 (AUS Eastern Daylight Time)');
So does anyone have any suggestions for the best way on how I can make this application timezone aware considering the server isn't set to UTC?
Many thanks, J.
This is not going to be very easy.
First of all, consider that existing stored dates are in local time of your server, which observes daylight saving time. Any code that has to do anything with these dates except just printing them, now or in the future, will need to convert them to UTC first. If the daylight saving rules are not exactly the same at the point in time where the date was stored and the current time (when the conversion is taking place), your server will use the "current" rules and therefore produce a wrong result. Granted, this scenario may be far-fetched in your specific case (or then again it might not), but it's a very strong warning against storing anything other than UTC.
Assuming that the DST rules remain constant, and that you have PHP >= 5.3.0, you can do this:
Read "original" database date with DateTime::createFromFormat, explicitly specifying the timezone (server's TZ)
Convert to user local time with DateTime::setTimezone (specifying user's TZ)
Display to the user
When receiving user input, you will need to do the reverse:
Create user local time date with with DateTime::createFromFormat, explicitly specifying the timezone (user's TZ)
Convert to server local time with DateTime::setTimezone (specifying server's TZ)
Store in database
Apart from the above, I would suggest taking your application offline at some point and convert all dates in the database to UTC. You would then be rid of the problem discussed earlier (at least in the future, as the past cannot be undone). The "server's TZ" I mention above would then be UTC (regardless of the fact that the actual server may be set to AUS EDT or not, your "working" timezone will be UTC).
You could make use of
1) date_default_timezone_set - Sets the default timezone used by all date/time functions in a script
2) Instead of using this function to set the default timezone in your script, you can also use the INI setting date.timezone to set the default timezone.
The important thing to keep in mind is not UTC, but that all times stored must be standardized to one timezone. So, if your PHP server and your database server both use the same timezone, the only issue that arises is when you need to display a location-aware time to the user or when you allow a user to enter a datetime from another timezone.
PHP has a nice, though somewhat scantly documented class, called DateTime. And some ancillary classes like DateTimeZone, DateInterval, etc. These make converting from db time to user time pretty simple.
So does anyone have any suggestions for the best way on how I can make this application timezone aware considering the server isn't set to UTC?
If you manage to come with any scheme for remapping the timezones its going to be horribly complicated and even more impossible to ever fix properly. Do yourself a favour and get the server timezone to UTC and fix your existing data.
First of allyou have to convert the date time selected by user to timestamp.
You have to use Server time zone offset and save the time to server in GMT.
This is the best way because while displaying the date just add the offset of the user
and convert and show.
I have implemented this for my client as it was an auction site and user may add item from AUS in his time and bidder will be from US. Time zone issues was there and we implemented after a lots of rerence.
You know one thing best and easy way is , do like ebay . just save the user time zone and show time with the time zone. No conversion nothing. Simple and better . 10:35 EST :)
If you wannabe perfect in time zone conversion, think about daylight saving time also. start date and end date on each year will change slightly. If you want to be accurate you have to save the daylight starting and ending date in db and add that difference too .:)
For working with datetime in different timezones and formats you can try to use PHP library Dater (https://github.com/barbushin/dater). Cheers!
I have just realised if I add a particular record to my MySQL database - it will have a date/time of the server and not the particular user and where they are located which means my search function by date is useless! As they will not be able to search by when they have added it in their timezone rather when it was added in the servers timezone.
Is there a way in Codeigniter to globally set time and date specific to a users location (maybe using their IP) and every time I call date() or time() that users timezone is used.
What I am actually asking for is
probably how to make my application
dependent on each users timezone?
Maybe its better to store each users timezone in their profile and have a standard time (servers time) and then convert the time to for each user?
Thanks all
It sounds like what you need to do is store all of the date and times in your system as UTC time (used to be called GMT). This is the base time that everything in the world is calculated off of with adjustments. (eg: Central Time is -6 hours off of UTC)
In MySQL you can use UTC_TIMESTAMP() to get the current UTC time as long as your server and DB are configured with the correct times and timezone settings.
In PHP run this to set the timestamp of PHP to UTC (you will run this in your code so put it on every page or in a centralized index file):
date_default_timezone_set('UTC');
Or you can go directly into PHP.INI and tell it to use UTC time globally. (this may not work if you have multiple websites on a single installation of PHP.
And then anywhere in the system you need to get the current UTC time you can just call:
time();
Then for each user in the system you will need to ask them what timezone they live in and then when you display times make the adjustment for that user. So if it is 5:00PM UTC and I live in Easter US (-5) the time would be 5:00 - 5 hours = 12:00PM.
This can be a long process to get right but once you do your users will find it very useful especially internationally.
I think the easiest way is define a timezone for internal data storage (your server's time zone or UTC) and convert the time according to the user's time zone when outputting it.
I don't know CodeIgniter so I can't point you to the right functions. One prominent library that is timezone aware is Zend_Date: Working with Timezones I have not worked with these functions yet but they look promising.
However, once you know the user's time zone, it's not difficult to put together an own function that adds/substracts the offset when outputting dates and/or times.
Possibly related question:
MySQL: keep server timezone or user timezone?
Take an example of an existing web application such as WordPress and phpBB. Each user have their own timezone setting.
When receiving a content from the user, use local_to_gmt() function in the Date Helper then save the content into database using the gmt date. When fetching the data you will get the time in gmt. Get the user's timezone setting, then display the data in that timezone.
This way, you can save yourself from calculating between two timezone. Just make sure that your server's time is in correct setting, so all your data is in the correct gmt time.
UPDATE:
Recently I review the last project I worked on that have timezone issue. After thinking various scenario, here is the solution for the timezone issue:
All data stored right now already
using server's time. Changing this
will takes times and prone to error,
so I leave it like that.
For the new data from user that set the content date to a certain
date and time, I stored it into 2
column. First column is to store the
data as is, and used to displaying
it as is. Second column will be a
recalculation of the date based on
the user's timezone into server's
timezone. This column is used in the
WHERE statement (filter based on
server date) and for the ORDER
(because this column's value all in
same timezone, which is the server's
timezone).
This way, I only do 1 timezone calculation, which is to convert user date into server date. For displaying , I display the date according to server's datetime. Since all data stored in the same timezone, data can be ordered by the column that hold the server date value.
For the user that have set their timezone, the date from database can be easily recalculated to get the datetime in the user's timezone. Btw, in my application, I display the date using timeago jquery plugins. This plugins need time in the ISO8601 format (UTC time). local_to_gmt() function in CodeIgniter can be used to do this.
Obviously the leap to British Summer Time (Daylight Savings Time) is a big confusion in the world of programming, and I am indeed caught up in that confusion.
The best possible solution I can find (which I will try to coherently explain) when using a timezone sensitive system is this:
The Web Server and Database should both be running off the same machine timezone. I suggest UTC as it is the building blocks of timezone conversions. This will ensure that all of the dates stored in your database are constant, and don't skip any times such as the 1hour jump between Daylight Savings.
At the top of all of your PHP scripts use date_default_timezone_set('Europe/London'); with the specific timezone of the user.
When producing dates from user submitted forms, use gmmktime(); to ensure that the timestamp created is UTC and not altered by the timezone that you have set.
date(); can be used when displaying dates, as this will convert the timestamp to the correct time taking into account the timezone that you have set.
If you do need to show a date in the UTC format then use gmdate(); with the $gm_timestamp that you have taken from the database or created with gmmktime();.
I have written this bit of PHP to help understand the situation.
date_default_timezone_set('UTC');
$gmtime = gmmktime(2,0,0,03,29,2009);
$time = mktime(2,0,0,03,29,2009);
echo $gmtime.'<br />'.date('r',$gmtime).'<br />'.gmdate('r',$gmtime).'<br />';
echo $time.'<br />'.date('r',$time).'<br />'.gmdate('r',$time).'<br />';
date_default_timezone_set('Europe/London');
$gmtime = gmmktime(2,0,0,03,29,2009);
$time = mktime(2,0,0,03,29,2009);
echo $gmtime.'<br />'.date('r',$gmtime).'<br />'.gmdate('r',$gmtime).'<br />';
echo $time.'<br />'.date('r',$time).'<br />'.gmdate('r',$time).'<br />';
Hopefully I've done a good job, but I doubt it because I'm still trying to battle the problem in my head.
UPDATE:
Glad I did this, because I am now having doubts about the user inputted dates.
To get the User inputted date (taking into account their timezone) to match up with the UTC corresponding date in the database, you should put it through mktime(). And then use gmdate('U', $timestamp); to get the true UTC timestamp. (I think)
Example
Looking at it from a reporting side, the user is using the 'Europe/London' timezone. At the start of our PHP script we call date_default_timezone_set('Europe/London');, whilst the Database (and all the records within) is still in UTC.
The user then sends through that they want to select a list of books added to the database between 25/03/2010 10:00 to 30/03/2010 14:00. The PHP script then runs the date variables through mktime($hour, $minute, $second, $month, $day, $year) to generate a correct UTC timestamp. The start date will not change, but PHP knows that the end date is within the BST timezone, so changes the timestamp to UTC accordingly.
When the results are returned back to the user, date('r', $date_added) can be used to show the user the date the book was added to the database according to their set timezone.
This link may help with understanding when it changes. http://www.daylightsavingtime.co.uk/
I think recalculating to user's time is better option, since it gives you normalized time on server, i.e. if you'll need to look up something, that happened (from your point of view) hour ago, you won't have a mess with american, asian and e.g. australian time.
Just ask them for their timezone (usually select with major cities in that timezone) and then recalculate :)
Or, alternatively, you can store two timedates - one for your comparison and one to show, so you won't have so much calculations on serverside.
Also, if recalculating, you can use date helper:
http://ellislab.com/codeigniter/user-guide/helpers/date_helper.html
I've used the MySQL built-in timezone conversion. In the database, all datetimes are stored as UTC. In the select query, I used CONVERT_TZ to convert to the user's timezone. You can specify timezone codes or hour invervals like:
SELECT CONVERT_TZ('2004-01-01 12:00:00','GMT','MET');
SELECT CONVERT_TZ('2004-01-01 12:00:00','+00:00','+10:00');
But, the problem is this does not accommodate for daylight savings times. This is particularly frustrating since many parts of the world either don't honor daylight savings or honor it on different dates. So, if you install the timezone description tables, you can use descriptive names that will account for daylight savings automatically like:
SELECT CONVERT_TZ('2004-01-01 12:00:00', 'UTC', 'US/Eastern');
Codeigniter contains a helper which deals with all manner of date functions.
Codeigniter Date helper
the command gmt_to_local() should help you... the third parameter is for 'daylight_saving'.
Takes a Unix timestamp (referenced to GMT) as input, and converts it to a localized timestamp based on the timezone and Daylight Saving time submitted. Example:
$timestamp = '1140153693';
$timezone = 'UM8';
$daylight_saving = TRUE;
echo gmt_to_local($timestamp, $timezone, $daylight_saving);
Add this line to autoload.php in the application folder/config folder:
$autoload['time_zone'] = date_default_timezone_set('Asia/Kolkata');