问题
I am having two date values, one already stored in the database and the other selected by the user using DatePicker. The use case is to search for a particular date from the database.
The value previously entered in the database always has time component of 12:00:00, where as the date entered from picker has different time component.
I am interested in only the date components and would like to ignore the time component.
What are the ways to do this comparison in C#?
Also, how to do this in LINQ?
UPDATE: On LINQ to Entities, the following works fine.
e => DateTime.Compare(e.FirstDate.Value, SecondDate) >= 0
回答1:
NOTE: at the time of writing this answer, the EF-relation was unclear (that was edited into the question after this was written). For correct approach with EF, check Mandeeps answer.
You can use the DateTime.Date property to perform a date-only comparison.
DateTime a = GetFirstDate();
DateTime b = GetSecondDate();
if (a.Date.Equals(b.Date))
{
// the dates are equal
}
回答2:
Use the class EntityFunctions for trimming the time portion.
using System.Data.Objects;
var bla = (from log in context.Contacts
where EntityFunctions.TruncateTime(log.ModifiedDate) == EntityFunctions.TruncateTime(today.Date)
select log).FirstOrDefault();
Source: http://social.msdn.microsoft.com/Forums/en-US/csharpgeneral/thread/84d4e18b-7545-419b-9826-53ff1a0e2a62/
UPDATE
As of EF 6.0 and later EntityFunctions is replaced by DbFunctions.
回答3:
I think this could help you.
I made an extension since I have to compare dates in repositories filled with EF data and so .Date was not an option since it is not implemented in LinqToEntities translation.
Here is the code:
/// <summary>
/// Check if two dates are same
/// </summary>
/// <typeparam name="TElement">Type</typeparam>
/// <param name="valueSelector">date field</param>
/// <param name="value">date compared</param>
/// <returns>bool</returns>
public Expression<Func<TElement, bool>> IsSameDate<TElement>(Expression<Func<TElement, DateTime>> valueSelector, DateTime value)
{
ParameterExpression p = valueSelector.Parameters.Single();
var antes = Expression.GreaterThanOrEqual(valueSelector.Body, Expression.Constant(value.Date, typeof(DateTime)));
var despues = Expression.LessThan(valueSelector.Body, Expression.Constant(value.AddDays(1).Date, typeof(DateTime)));
Expression body = Expression.And(antes, despues);
return Expression.Lambda<Func<TElement, bool>>(body, p);
}
then you can use it in this way.
var today = DateTime.Now;
var todayPosts = from t in turnos.Where(IsSameDate<Turno>(t => t.MyDate, today))
select t);
回答4:
If you use the Date property for DB Entities you will get exception:
"The specified type member 'Date' is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported."
You can use something like this:
DateTime date = DateTime.Now.Date;
var result = from client in context.clients
where client.BirthDate >= date
&& client.BirthDate < date.AddDays(1)
select client;
回答5:
To do it in LINQ to Entities, you have to use supported methods:
var year = someDate.Year;
var month = ...
var q = from r in Context.Records
where Microsoft.VisualBasic.DateAndTime.Year(r.SomeDate) == year
&& // month and day
Ugly, but it works, and it's done on the DB server.
回答6:
Here's a different way to do it, but it's only useful if SecondDate is a variable you're passing in:
DateTime startDate = SecondDate.Date;
DateTime endDate = startDate.AddDays(1).AddTicks(-1);
...
e => e.FirstDate.Value >= startDate && e.FirstDate.Value <= endDate
I think that should work
回答7:
You can also use this:
DbFunctions.DiffDays(date1, date2) == 0
回答8:
you can use DbFunctions.TruncateTime() method for this.
e => DbFunctions.TruncateTime(e.FirstDate.Value) == DbFunctions.TruncateTime(SecondDate);
回答9:
Just always compare the Date property of DateTime, instead of the full date time.
When you make your LINQ query, use date.Date in the query, ie:
var results = from c in collection
where c.Date == myDateTime.Date
select c;
回答10:
This is how I do this.
DateTime date_time_to_compare = DateTime.Now;
//Compare only date parts
context.YourObject.FirstOrDefault(r =>
EntityFunctions.TruncateTime(r.date) == EntityFunctions.TruncateTime(date_to_compare));
回答11:
//Note for Linq Users/Coders
This should give you the exact comparison for checking if a date falls within range when working with input from a user - date picker for example:
((DateTime)ri.RequestX.DateSatisfied).Date >= startdate.Date &&
((DateTime)ri.RequestX.DateSatisfied).Date <= enddate.Date
where startdate and enddate are values from a date picker.
回答12:
Without time than try like this:
TimeSpan ts = new TimeSpan(23, 59, 59);
toDate = toDate.Add(ts);
List<AuditLog> resultLogs =
_dbContext.AuditLogs
.Where(al => al.Log_Date >= fromDate && al.Log_Date <= toDate)
.ToList();
return resultLogs;
回答13:
You can user below link to compare 2 dates without time :
private bool DateGreaterOrEqual(DateTime dt1, DateTime dt2)
{
return DateTime.Compare(dt1.Date, dt2.Date) >= 0;
}
private bool DateLessOrEqual(DateTime dt1, DateTime dt2)
{
return DateTime.Compare(dt1.Date, dt2.Date) <= 0;
}
the Compare function return 3 different values: -1 0 1 which means dt1>dt2, dt1=dt2, dt1
回答14:
Try this... It works fine to compare Date properties between two DateTimes type:
PS. It is a stopgap solution and a really bad practice, should never be used when you know that the database can bring thousands of records...
query = query.ToList()
.Where(x => x.FirstDate.Date == SecondDate.Date)
.AsQueryable();
来源：https://stackoverflow.com/questions/1478215/how-to-compare-only-date-components-from-datetime-in-ef