It's about an Cordova application.
On start I request a json php file, which contains several Datetime strings, which were pulled from my DB. The dates have been filled in manually by someone in (CET/MEZ summer: GMT+2) Timezone.
The way I see it, the DB does not store any timezone info for datetime's(?).
For example I have this datetime in my DB:
2014-05-22 19:45:00
In my application this date represents the start of an event. The user can now enable notifications. Which works fine when I test it.
But what about someone in an other timezone (e.g. Brazil, GMT-3, so it should be 2014-05-22 14:45:00). I don't know how to test that.
Would the date from the json php file adjust to the timezone? I guess not. So I thought about just doing SELECT UNIX_TIMESTAMP(event_datetime). Would that do the trick?
Thank you for taking the time to read this. I appreciate every answer.
Both UNIX timestamps and MySQL's DATETIME data type are stored as UTC (no time zone information).
However, you may have saved the timestamps in the database without adjustment for the time zone. If all data has been entered in CEST (CET summer time), you can quickly adjust it.
PHP has some timezone features that can help you.
My suggestion is that you 1) adjust the timestamps in the database for the timezones, 2) output the JSON-data as UTC and 3) adjust it to the user's current time zone.
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've been looking around for a few hours now about what's the best way to use timezones in a PHP/MySQL web application, finding a definitive answer is hard. From what I've learnt so far it is best to store everyones stuff in the database in UTC (correct me if I am wrong).
When a user registers I will ask them for there timezone and then store that against there user. This would be in this format as a dropdown menu:
<option value="Europe/London">(GMT) Greenwich Mean Time : London</option>
The app I am building will allow users to set arrangements in the future with people (meetings), much like a calendar. Obviously over the course of a year different timezones have different daylight savings periods, any idea how I would cater for this?
Say a user from the UK sets a meeting for 3:00PM on January 24th 2013 and invites someone who lives in California to this meeting, how do I get it so that the American sees that meeting in his/her timezone and the UK user sees it in his/her timezone? (Note that both users are signed up and have set their timezone).
Does anyone have a clear explanation and maybe some examples for this? Or can point me to where I can find that?
Thanks
I dealt with this situation extensively in a PHP/MySQL application I wrote for a private jet operator a little over a year ago. There are different strategies to handle timezones in these two platforms, but I will explain how I did it. I set the MySQL server to UTC and run each PHP script in the timezone that the user specifies during the signup process for the user profile.
MySQL and PHP (PHP 5.2 and above) both have native datetime datatypes. MySQL's datetime is a primitive data type, while PHP 5.2 and above offers the built-in DateTime class. The MySQL datetime datatype does not include metadata for the timezone, but a PHP DateTime object always includes a timezone. If the PHP datetime constructor does not specify the optional timezone in the second argument, then the PHP datetime constructor uses the php environment variable.
Both MySQL and PHP have default timezone set in the configuration files. MySQL uses the datetime set in the config file for each db connection unless the user specifies a different timezone after connection is started with the command SET time_zone = [timezone];. PHP also sets a timezone environment variable for each script using the timezone set in the server config file, and this environment variable can be overriden using the PHP function date_default_timezone_set() after the script starts.
The PHP DateTime class has a property called timezone, which is a PHP DateTimeZone object. The DateTimeZone object is specified using a string for the exact time zone. The list of timezones is comprehensive, having hundreds of individual time zones across the world. The PHP time zones will account for daylight savings time automatically.
When the user generates a datetime in the web app, construct a PHP datetime object in the timezone of the user's profile. Then use the setTimezone method to modify the DateTime object to the UTC timezone. Now you have the user's datetime in UTC, and you can store the value in the database. Use the DateTime format method to express the data as a string in the format accepted by MySQL.
So the user generates a datetime, and you make a PHP datetime object in the user's specified timezone:
// set using an include file for user profile
$user_timezone = new DateTimeZone('America/New_York');
// 1st arg in format accepted by PHP strtotime
$date_object1 = new DateTime('8/9/2012 5:19 PM', $user_timezone);
$date_object1->setTimezone(new DateTimeZone('UTC'));
$formated_string = $date_object1->format('Y-m-d H:i:s');
$query_string = "INSERT INTO `t_table1` (`datetime1`) VALUES('$formated_string')";
When you retrieve the value from the database, construct in UTC and then convert to the user's time zone.
$query_string = "SELECT `datetime1` FROM `t_table1`";
$date_object1 = new DateTime($datetime_string_from_mysql, new DateTimeZone('UTC'));
$date_object1->setTimezone($user_timezone);
$string_for_display_in_application = $date_object1->format('m/d/Y g:i a');
Using this method, your datetime values are always stored in UTC inside the db, and the user always experiences the values in his/her profile's time zone. PHP will correct for Daylight Savings Time if necessary for each time zone.
One gotcha: This explanation does not cover the MySQL timestamp datatype. I recommend using the MySQL datetime datetype to store datetime values, not the timestamp datatype. The timestamp datatype is covered in the manual here.
Edit:
You can produce an array containing every PHP timezone string using listIdentifiers, which is a static method of the DateTimeZone class.
In MySQL, what you need to do is:
Store each user's chosen timezone someplace you can retrieve it when you're doing database queries on behalf of that user. You can store it as a string.
Right before you do work on behalf of a particular user (for example, storing or retrieving appointment times and dates) do SET time_zone = (stored time zone setting)
This will cause time zones to be converted appropriately to each person's local time.
Edit:
This works because
MySQL tries to use UTC (universal time, formerly known as Greenwich Mean Time) to store DATETIME and TIMESTAMP data items in tables.
It can only do this correctly if it knows the correct local time zone for each data item it is given by applications.
In applications that don't care about different time zones, it does this in a MySQL-server-wide way. See https://dev.mysql.com/doc/refman/5.5/en/time-zone-support.html . Most people who run multi-national and multi-time-zone applications set their server time zones to UTC, not to local time, because it makes it much easier to keep things sorted out.
It makes very little sense to try to convert a time from UTC to local time unless you also know the date and the timezone, because local time switches on and off at various times of year. Just try to get this right for all three of Israel, Arizona, and New York, I dare you! Israel switches between daylight and standard time on Passover and Rosh Hashanah; Arizona doesn't switch, and New York switches at the whim of the US federal legislature.
There's a session-scope time_zone setting (SET time_zone = something). If you don't set it, it uses the timezone representation in item 3 above. If you set it, the server will use this as the timezone to convert its internal representation to the representation it sends back in queries.
You can get a list of the names of the available time zones in your MySQL server by issuing SELECT Name from mysql.time_zone_name. This can populate the pulldown menu from which your user can select her time zone. If this query returns no items, take a look at bottom of https://dev.mysql.com/doc/refman/5.5/en/time-zone-support.html .
So, that means you can set your session time_zone setting to a particular user's time zone, and then get back all times in that user's time zone. Also, any DATETIME or TIMESTAMP items you INSERT or UPDATE will be converted from that user's time zone to MySQL's internal representation as they are placed in your tables.
Be careful: in web applications with persistent MySQL connections, the work for a new user request will inherit the connection's time_zone setting. Don't forget to reset it for the new user.
If you're running a query returning local time data for more than one user, and those users happen to be in different time zones, you can't take advantage of this MySQL per-session feature set. You can work around this by running different queries for different users and changing the time_zone setting between them.
Or, you can use the MySQL function
CONVERT_TZ(datetime,'UTC','user_time_zone')
or similar on each item.
Alternatively, Java and DotNET have their own high-quality time zone manipulation systems. So, you can make the choice of running your MySQL server with the time_zone setting of UTC, and do all your timezone conversions in your application.
In my LAMP application, I'm storing certain date/time stamps using the timestamp data type in MySQL. From my understanding, this will automatically convert to UTC when saving and converted back from UTC when retrieving. The conversion back from UTC depends on the time zone settings of the server where MySQL is installed, right?
What if I want the timestamp converted into whatever time zone my user is in? How do I query SQL to return those timestamps into a specified time zone? My server's time zone is useless to my users, unless they so happen to be in the same timezone I guess.
Similar to this question ( Detect user timezone and display UTC time with that timezone ) , you can do it as follow :
Detect user timezone offset
Calculate the difference between MySQL / Web Server's timezone
Apply your logic
UPDATE: another related question here : Determine a User's Timezone
I think you want the CONVERT_TZ function .
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');