In my database the date is stored like datetime but when I want to perform a search/filtering I want it to be based only on the date ignoring the exact time. I spend a lot of time figuring out how to do it and finally I got a working solution on my own :
string val = rule.Data;
if (!string.IsNullOrEmpty(val))
{
switch (rule.Field)
{
case "Date": {
DateTime parsedDate = DateTime.ParseExact(
val,
"dd/MM/yyyy",
CultureInfo.InvariantCulture);
var pYear = parsedDate.Year;
var pMonth = parsedDate.Month;
var pDay = parsedDate.Day;
rows = rows.Where(o => o.Date >= parsedDate && o.Date <= new DateTime(pYear, pMonth, pDay, 12, 59, 40)); break;
}
}
}
This is working Ok. It needs a little change but I think I can use the code above. However today a college of mine pass me a solution which is from a previous project being developed here, and this solution is a lot shorter and I would prefer to use it if possble. It looks like this:
string val = rule.Data;
if (!string.IsNullOrEmpty(val))
{
switch (rule.Field)
{
case "Date": { rows = rows.Where(o => o.Date.ToString("dd/MM/yyyy") == val); break; }
}
}
The code doesn't break when I try this but it's not filtering data too. I always get empty result. I guess that o.Date.ToString("dd/MM/yyyy") is where the problem lies. I don't know is it ok to use ToString() like this for DateTime object. In the example I'm using ToString() also get a format type like the one I'm providing here - ToString("dd/MM/yyyy") - but in my case ToString() is not overloaded anywhere. Is this a standard way to manipulate DateTime objects or I just can't find the place where ToStrin() is predefined. And finally, can you provide me with a working example based on the code above.
Depending on what culture o.Date is, Try:
string val = rule.Data;
if (!string.IsNullOrEmpty(val))
{
switch (rule.Field)
{
case "Date":
{
rows = rows.Where(o => o.Date.ToString("dd/MM/yyyy", CultureInfo.InvariantCulture) ==
DateTime.ParseExact(val,
"dd/MM/yyyy",
CultureInfo.InvariantCulture));
break;
}
}
}
Or you could set the culture of the current thread instead:
Thread.CurrentThread.CurrentCulture = System.Globalization.CultureInfo.InvariantCulture;
Edit: It should work if you avoid using strings:
e.g.
DateTime maxDate = new DateTime(2020, 11, 17);
if (DateTime.Now.Date > maxDate)
{
// this will just work regardless of setting culture
}
I think if you need to compare dates then you can just get a Date component of a DateTime and compare it to your predefined value. This should be faster as there won't be a need to transform date to string every time as well. So you can first get your reference value like that DateTime.ParseExact(value, "dd/MM/yyyy", CultureInfo.InvarianCulture). You can just use a constructor of a DateTime to compose it as well.
You shouldn't have to use strings at all. If it is a datetime (or similar) in the database, and a DateTime in your c# code, then there is never a good reason to use a string as an intermediate step.
Also, you should pay close attention to the .Kind property of your DateTime values. And you should never be comparing local times against DateTime.Now. If you do, you may introduce errors during daylight saving time transitions. Instead, you should use UTC DateTime values, or use DateTimeOffset values instead. Read more here.
Related
I'd like to take a datetime string, and get the string version of its format:
e.g. 2017-01-02 would yield YYYY-MM-dd for logging purposes if a datetime is parsed incorrectly due to a parsing exception.
Is this possible with System.DateTime or any other built-in?
"2017-01-02" would yield "YYYY-MM-dd"
It's not possible. You are asking for magic, making something out of nothing.
There is no way without meta information for a computer (or a human) to decide if that is the 2nd January or the 1st February. Both is possible.
There is no reliable way of getting that format string based on a string that might look like a date.
The closest hack that I can come up with is iterating over all cultures and then trying to ParseExact the predefined DateTime patterns that are found in each culturinfo's DateTimeFormat property.
The hack would look like this:
var date = "2017-01-02";
var formats = new Dictionary<string,int>();
// go over all cultures
foreach(var ci in CultureInfo.GetCultures(CultureTypes.SpecificCultures))
{
// each culture has a DateTimeFormatInfo that holds date and time patterns
foreach(var p in typeof(DateTimeFormatInfo)
.GetProperties()
.Where(prop => prop.Name.EndsWith("Pattern")))
{
// get a pattern property from the cultureinfo DateTimeFormat
var fmt = (string) p.GetValue(ci.DateTimeFormat, null);
try
{
// try to parse the date
DateTime.ParseExact(date,fmt , ci);
// add the format
if (formats.Keys.Contains(fmt))
{
formats[fmt]++; // how often this was a valid date
}
else
{
formats.Add(fmt, 1); // first time we found it
}
}
catch
{
// no date in this culture for this format, ignore
}
}
}
// output the formats that were parsed as a date
foreach(var kv in formats)
{
// Dump is a linqPad extension, use Console.WriteLine if that bothers you
kv.Value.Dump(kv.Key);
}
and on my box this returns
yyyy-MM-dd
40
yyyy-M-d
1
Now for 01/02/2017 it would return:
dd/MM/yyyy
255
d/M/yyyy
93
M/d/yyyy
20
d/MM/yyyy
11
MM/dd/yyyy
2
which shows a bit of the concerns raised in the comments. Without knowing the culture a date string was generated it is a guess what the date format was. Worst case it was a string with numbers and dashes between them.
i came across a situation that, i need to get only the Date out from DateTime.
i am having a DateTime? StartDate property (Nullable) used to hold the date value
i tried below,
var d = Convert.ToDateTime(StartDate).Date;
but its returning me d as eg. 6/22/2006 12:00:00AM
after doing var d = Convert.ToDateTime(StartDate).Date.ToString("d");
i'm able to get d as 6/22/2006..but i dont want to convert my DateTime? to String
is their any way to get only the Date without using the ToString("d")?
Use the Date property to get the Date component of DateTime instance:
DateTime dateTimeNow = DateTime.Now;
DateTime datePartOnly = dateTimeNow.Date; // Return 00/00/0000 00:00:00
With this approach, Date property will return the date at midnight. So the time part will be 00:00:00 in this case.
There are couple of alternate ways to get the just the Date part, but the return type of it will be a string:
1.) Using .ToString(string? format) where format can be standard or custom format string
string dateOnlyString = dateTimeNow.ToString("dd/MM/yyyy");
//Can also use .ToString("dd-MM-yyyy");
2.) Using .ToShortDateString() to return a culture sensitive date string
string dateOnlyString = dateTimeNow.ToShortDateString();
//Returns M/d/yyyy for "en-US" culture
//Returns yyyy/M/d for "ja-JP" culture
Reference: here.
try this:
string x = DateTime.Now.ToShortDateString().
this will get the date dd/mm/yy given to the string x.
I think you question is sort of... moot.
You ask for a date without a time, but get a DateTime, which has both. I really don't think that should be a problem in most cases though:
If you create a DateTime with a certain date, and compare it to another date, and both of these have their time set to midnight, your comparisons will be valid and correct. Eg:
var yesterday = new DateTime(2014, 3, 10);
var today = new DateTime(2014, 3, 11);
var tomorrow = new DateTime(2014, 3, 12);
Comparing and sorting these will work as you expect, and so will the following:
if(today == DateTime.Today){
Console.WriteLine("Today is the day!");
}
In other words, you should be perfectly fine just pretending like the time-part does not exist.
Also, as you touched upon yourself in the OP, you can use the property Date if you want to make sure to avoid any time-component:
// Note the addition of hours, minutes and seconds:
var today = new DateTime(2014, 3, 11, 14, 35, 33);
if(today == DateTime.Today){
Console.WriteLine("This never happened...");
}
if(today.Date == DateTime.Today){
Console.WriteLine("...But today is still the day!");
}
In C# 10 you can use DateOnly.
DateOnly date = DateOnly.FromDateTime(DateTime.Now);
A DateTime does have both a date and a time. You can decide with yourself that in a specific property you well never use the date part. It will just be 12:00 AM, but you won't use it.
In some situations it can be useful to write your own type that can never hold a time-of-day component. Here is a start:
struct Date : IFormattable
{
readonly DateTime value;
public Date(DateTime dateAndTime)
{
value = dateAndTime.Date;
}
public string ToString(string format, IFormatProvider formatProvider)
{
return value.ToString(format ?? "d", formatProvider);
}
public string ToString(string format)
{
return ToString(format, null);
}
public string ToString(IFormatProvider formatProvider)
{
return ToString(null, formatProvider);
}
public override string ToString()
{
return ToString(null, null);
}
public static implicit operator DateTime(Date date)
{
return date.value;
}
}
The field value does hold the 12 AM thing, but it is private and is not seen from the outside. The overloads of ToString() make sure that unless something else is requested, the Date is written out with the short date format of the current culture.
I got 2 textboxes, and want to calculate the difference of the time between those 2.
And i got it working, but it´s barely, at least i think i just made it working with some "hacks".
It will also fail if something is not correct, and will throw an exception, which i would like to prevent (probably with an IF, to just ignore if it´s not correct).
Here is the code:
private void button1_Click(object sender, EventArgs e)
{
try
{
var first = TimeSpan.ParseExact(First.Text.Replace("-", ":").Remove(First.Text.LastIndexOf("-"), 1).Insert(First.Text.Length - 4, "."), "g", CultureInfo.InvariantCulture);
var last = TimeSpan.ParseExact(Last.Text.Replace("-", ":").Remove(First.Text.LastIndexOf("-"), 1).Insert(First.Text.Length - 4, "."), "g", CultureInfo.InvariantCulture);
var difference = first - last;
CalcDiff.Text = difference.TotalSeconds.ToString("F3");
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
AS you can see, it´s many "replace" and all kinds of stuff, just to make it work.
The formatting i am providing is this:
2013-05-22 12-07-55-324
And for that matter, i only care about the time, which is: 12-07-55-324
So, i am telling it to replace - with :, to just make itwork, and stuff like that.
So, is there a way to improve that. And can i make some kind of Condition, so i can´t just, press the button, and it will fail if it´s not correct (for example the formatting is wrong, or it´s nothing there, or Text instead).
You can use TimeOfDay of a DateTime which can be parsed via DateTime.ParseExact:
string dtString = "2013-05-22 12-07-55-324";
TimeSpan ts = DateTime.ParseExact(dtString, "yyyy-MM-dd HH-mm-ss-fff", CultureInfo.InvariantCulture).TimeOfDay;
DEMO
You can use DateTime.TryParseExact to check if the string can be parsed successfully:
DateTime firstDt;
DateTime lastDt;
if ( DateTime.TryParseExact(First.Text, "yyyy-MM-dd HH-mm-ss-fff", CultureInfo.InvariantCulture, DateTimeStyles.None, out firstDt )
&& DateTime.TryParseExact(Last.Text, "yyyy-MM-dd HH-mm-ss-fff", CultureInfo.InvariantCulture, DateTimeStyles.None, out lastDt ))
{
// successfully parsed both Datetimes
var difference = firstDt.TimeOfDay - lastDt.TimeOfDay;
CalcDiff.Text = difference.TotalSeconds.ToString("F3");
}
Here is a more readable approach since you are concerned about complexity of the if-statement:
DateTime firstDt, lastDt;
bool canParseFirst = DateTime.TryParseExact(First.Text, "yyyy-MM-dd HH-mm-ss-fff", CultureInfo.InvariantCulture, DateTimeStyles.None, out firstDt);
bool canParseLast = DateTime.TryParseExact(Last.Text, "yyyy-MM-dd HH-mm-ss-fff", CultureInfo.InvariantCulture, DateTimeStyles.None, out lastDt );
if(canParseFirst && canParseLast)
{
// successfully parsed both Datetimes
var difference = firstDt.TimeOfDay - lastDt.TimeOfDay;
CalcDiff.Text = difference.TotalSeconds.ToString("F3");
}
else
{
// inform the user
}
You should use DateTime instead, you'll still be able to get the difference in the two times pretty easily (just Google finding the difference between two DateTime objects), plus you can use TryParseExact to specify strange formats like you have there. PLUS that method will help alleviate those pesky exceptions you mentioned! Instead of throwing an exception, it will simply return true if it parsed successfully and false otherwise.
I have a Datetime object which I take from an XML file (closingDate).
I want to dynamically display all closingDates to the user. However, not all objects in the XML file necessarily contain a dateobject.
How can I do this (pseudocode):
DateTime closingDate = DateTime.Parse(xmlFile.selectSingleNode("Closing_Date")).toString();
and then later, I am writing out an HTML file with:
String fileListHTML += "<li><a href='#'>The file name gets put here</a> (Closed:
"+closingDate+")</li>";
Now, as long as there is a datetime, there is no issue. However, if there is no datetime object (ie: null), I get an error.
Can I somehow do an if statement to say (again, pseudo):
if (closingDate =="")
{
closingDate = "To be determined";
}
I am, of course, getting an error about casting a datetime to string.
Is there a way to do this?
I'm not a fan of turning DateTimes to strings until it is necessary.
You could use a nullable DateTime. Use null to denote it's not set or parsable. Alternatively scratch the nullable approach and use a sentinel such as DateTime.MinValue instead.
This is untested but should get the point across:
DateTime? closingDate;
if (!string.IsNullOrEmpty(myClosingDateString))
{
closingDate = DateTime.Parse(myClosingDateString);
}
// do whatever else you need
// when it comes time to appending ...
if (!closingDate.HasValue) // or check if it's `DateTime.MinValue`
{
fileListHtml += "No closing date";
}
else
{
fileListHtml += closingDate.Value.ToString();
}
I'd caution you to be careful about converting DateTime to strings without considerations to time zones and internationalization (for example, DateTime.Parse() can interpret dates very differently depending on regional settings and/or the culture you pass in).
For simplicity, if you can control the format of the string, I'd suggest using UTC and the ISO 8601 format.
Use DateTime.TryParse instead, here's a sample code showing how it works:
DateTime res;
if ( DateTime.TryParse(str,out res))
{
// Res contain the parsed date and you can do whatever you want with
}
else
{
// str is not a valid date
}
http://msdn.microsoft.com/fr-fr/library/ch92fbc1.aspx
Is there a way, a good way, to test if a string than I want to transform in DateTime is dd/MM/yyyy or MM/dd/yyyy ?
Thanks,
No, because it could be both. Is 11/10/2010 November 10th or October 11th?
Yes, in some cases (if one number is above 12) it will be unambiguous - but I think it's better to force one format or the other. If you just treat anything which can be done as MM/dd/yyyy that way, and move on to dd/MM/yyyy if it fails (or the other way round) then you'll get some very surprised users.
If this is part of a web application or something similar, I would try to make it completely unambiguous by using month names instead of numbers where possible.
No, but you could try both when parsing:
DateTime result;
if (DateTime.TryParseExact(
"05/10/2010",
new[] { "MM/dd/yyyy", "dd/MM/yyyy" },
CultureInfo.InvariantCulture,
DateTimeStyles.None,
out result)
)
{
// successfully parsed date => use the result variable
}
This problem will exist until all accepts and uses the ISO way. I'm a Swedish programmer working a lot with American and English clients and it's surprisingly hard to get these clients to use the standardized date format.
ISO 8601 - Use it!
Take a look at DateTime.ParseExact and DateTime.TryParseExact.
string date1 = "24/12/2010";
CultureInfo provider = CultureInfo.InvariantCulture;
DateTime dt1 = new DateTime(1, 1, 1);
bool dt1Valid = false;
try
{
dt1 = DateTime.ParseExact(date1, "dd/MM/yyyy", provider);
dt1Valid = true;
}
catch
{
dt1Valid = false;
}