In linq how can i diffentiate the date, like in sql we use
datediff(mm,getdate(),getdate())=0
now how can i write in linq, can any body help me thank you.
I think this is what you want:
var query = from entity in entities
where entity.SomeDateTime.Date == anotherDateTime.Date
select entity;
This only compares dates and not times.
You can use this code for comparing two dates using linq in C#
DateTime d1 = myDate1;
DateTime d2 = myDate2;
TimeSpan t1 = d2.Subtract(d1);
totalDays = t1.Days;
There's nothing special in Linq about date and time handling, so we should look at the plain .Net facilities.
A DateTime in C# is a date and time.
To get just the date component in C#, try this:
var now = DateTime.UtcNow; // or DateTime.Now for local time/day
DateTime today = now.Date;
This will give you the date and time at midnight of the same day.
If you want to get the difference in days between two DateTime objects:
public TimeSpan DiffDates(DateTime d1, DateTime d2)
{
return d1.Date - d2.Date;
}
// ...
if(DiffDates(dateTime1, dateTime2) == TimeSpan.Zero)
{
// ...
}
Alternately you could check directly if the dates are equal:
if(dateTime1.Date == dateTime2.Date)
{
// ...
}
If you skip the .Date property, then you will get incorrect results.
Related
I have the following code:
DateTime timeStamp = Convert.ToDateTime(Request.QueryString["TimeStamp"]);
var result = (from rs in db.VRec
where
rs.TimeStamp == timeStamp &&
rs.Fixure == wFixture
select rs).ToList();
The result shows 0 even though the correct timeStamp is passed.
If I remove the part where I do the TimeStamp comparison:
rs.TimeStamp == timeStamp
The code works fine.
Any idea on why the datetime comparison may not be working?
DateTime has a pretty fine resolution - likely you are comparing timestamps that only differ in milliseconds, which will fail. You probably want something like:
DateTime now = DateTime.Now;
DateTime then = now.Add(TimeSpan.FromMilliseconds(1));
const int EPSILON_MS = 10;
if(now.Subtract(then).TotalMilliseconds < EPSILON_MS)
{
Console.WriteLine("More or less equal!");
}
Linq converts DateTime arguments to DateTime2 in the sql query executed.
That is, when you do the comparison the actual sql executed will compare a DateTime to a DateTime2. This comparison will "cast" the DateTime to a DateTime2 and the millisecond part will be expanded to a greater resolution (in an odd way in my opinion, please enlighten me).
Try to execute the following sql:
declare #d1 datetime = '2016-08-24 06:53:01.383'
declare #d2 datetime2 = '2016-08-24 06:53:01.383'
declare #d3 datetime2 = #d1
select #d1 as 'd1', #d2 'd2', #d3 'converted'
select (case when (#d1 = #d2) then 'True' else 'False' end) as 'Equal',
(case when (#d1 > #d2) then 'True' else 'False' end) as 'd1 greatest'
From the question, I do not know if you want to compare the date with time or only the date part. If you only want to compare date then following would work
var result = (from rs in db.VRec
where
rs.TimeStamp.Date == timeStamp.Date &&
rs.Fixure == wFixture
select rs).ToList();
Since you are using some reference to db, it gives me a feeling that you are fetching your records from database (which ORM you are using is not obvious from the question or tags). Assuming that you are using Entity framework the above query will fail with exception that .Date has no direct translation to sql. If so you can rewrite the query as following to make it work.
var result = (from rs in db.VRec
where
rs.TimeStamp.Day == timeStamp.Day &&
rs.TimeStamp.Month == timeStamp.Month &&
rs.TimeStamp.Year == timeStamp.Year &&
rs.Fixure == wFixture
select rs).ToList();
The benefit of this approach is that you can compare properties to arbitrary deep level i.e you can compare Hours, Minutes,Seconds etc. in your query. The second query is tested in Entity framework 5.
My Linq to entities query is written as below.
The datatype of DATECOLUMN1 in my ORACLE database is of string.
Datetime FilterStartDate = DateTime.Now;
var query = from c in db.TABLE1
join l in db.TABLE2 on c.FK equals l.PK
where (FilterStartDate >= DateTime.ParseExact(l.DATECOLUMN1, "dd/MM/yyyy", CultureInfo.InvariantCulture) : false) == true
select c;
Writing above query gives me an error of not supported. How can I convert DATECOLUMN1 into a datetime to compare it.
P.S. I do not have control over database schema, so changing datatype of column in Oracle database is not a feasible solution for me.
In you Model, add the following property to your partial class TABLE2:
public DateTime DATECOLUMN1_NEW
{
get
{
return DateTime.ParseExact(DATECOLUMN1, "dd/MM/yyyy", CultureInfo.InvariantCulture);
}
set { }
}
Then, in you LINQ query, use DATECOLUMN1_NEW (it's already in DateTime format) in place of DATECOLUMN1.
Erm.. I think the problem you are having is that you are putting ": false" in there.
It looks like you are trying to use a condtional operator (?:) but you forgot the "?".
I don't think you actually need this as you are just trying to determine if the date is greater or not. Also if ParseExact fails it will throw an exception (not what you want) so you should use TryParse instead and handle the true/false returned and the out value to determine whether or not the date is (a) Actually a date (b) less then FilterStartDate.
You can use two alternatives:
Use the function described in the answer here: How to I use TryParse in a linq query of xml data?
Use the following fluent syntax version which I think is more readable.
var query = db.Table1.Join(db.Table2, x => x.FK, y => y.PK, (x, y) => x).Where(x =>
{
DateTime Result;
DateTime.TryParse(x.Date, out Result);
return DateTime.TryParse(x.Date, out Result) && FilterStartDate >= Result;
});
I’m trying to retrieve dates from the database then use it to compare with current date. How can I get the last date from a list of dates in the database then compare it with the current date? Here’s what I’ve tried but I get a exception: “LINQ to Entities does not recognize the method 'System.DateTime Last…”
var manageDate= from d in db.Enrollments.Select(da=>da.Date) select d;
var manageAssgnDate = from asgn in db.Enrollments.Select(asgn => asgn.Date) select asgn;
List<DateTime> newDate = manageDate.ToList();
I normally use lambdas:
// This gets the max date in the table
var manageDate = db.Enrollments.Max(da => da.Date);
Is this what you were asking for ?
Found a work-around:
var stdAssgn= from sa in db.Assignments where sa.StudentId==currentId select sa.Date;
var dt = stdAssgn.ToList().Last ();
String a = dt.ToString();
and to convert to DateTime if needed...
DateTime b=Convert.ToDateTime(a);
I want a linq query to return a calculated timespan,
i have used the timespan function before, but im not sure how to incorporate it into linq.
Basically the linq is returning a datetime field which i want to subtract from the current datetime to get days and hours.
Any help appreciated!
Thanks
Maybe something like:
from s in something
select DateTime.Now.Subtract(s.DateField)
Sure, the code below returns a date opened field, i want to calculate how many days the case is open and put it into a gridview.
var query2 = from cs in db.tblCases
where cs.date_closed.HasValue == false
select new
{
cs.date_case_opened),
};
gvReport.DataSource =
query2.Select(o => new {o.time });
gvReport.DataBind();
lbCount.Text = "Days open: " + ???
With this code:
i.SpesaAlloggio = db.TDP_NotaSpeseSezB.Sum(p => p.Costo / (((DateTime)p.DayEnd)
.Subtract((DateTime)p.DayStart).Days + 1));
I receive this error:
LINQ to Entities does not recognize the method
'System.TimeSpan Subtract(System.DateTime)' method, and this method cannot be
translated into a store expression.
How can I do this?
Use a calculated DB field and map that. Or use SqlFunctions with EF 4 as LukLed suggested (+1).
I wrote a function for removing time:
public static DateTime RemoveHours(DateTime date)
{
int year = date.Year;
int month = date.Month;
int day = date.Day;
return new DateTime(year, month, day);
}
and changed filtering condition:
var query =
from trn in context.IdentityTransactions
where trn.ClientUserId == userId && trn.DateDeleted == null
orderby trn.DateTimeCreated
select new
{
ClientServerTransactionID = trn.ClientServerTransactionID,
DateTimeCreated = trn.DateTimeCreated,
ServerTransDateTime = trn.ServerTransDateTime,
Timestamp = trn.Timestamp,
Remarc = trn.Remarc,
ReservedSum = trn.ReservedSum,
};
if (dateMin.HasValue && dateMin.Value > DateTime.MinValue)
{
DateTime startDate = Converters.RemoveHours(dateMin.Value);
query = from trn in query
where trn.DateTimeCreated >= startDate
select trn;
}
if (dateMax.HasValue && dateMax.Value > DateTime.MinValue)
{
var endDate = Converters.RemoveHours(dateMax.Value.AddDays(1.0));
query = from trn in query
where trn.DateTimeCreated < endDate
select trn;
}
dateMin and dateMax are nullable types and may be not set in my case.
Try (it is not very efficient, but it will work):
i.SpesaAlloggio = db.TDP_NotaSpeseSezB.ToList()
.Sum(p => p.Costo / (((DateTime)p.DayEnd)
.Subtract((DateTime)p.DayStart).Days + 1));
EDIT : This will be extremely slow for large tables, because it transfers whole table content form server
Entity Framework tries to translate your expression to SQL, but it can't handle ((DateTime)p.DayEnd).Subtract((DateTime)p.DayStart). You have to make it simpler. ToList() gets all rows and then makes the calculation on application side, not in database.
With EF4, you could use SqlFunctions DateDiff
With EF1, you could create calculated field or view with this field and make calculation based on this field.