Simple way to compare Dates in DateTime attribute using Entity Framework 4 and Linq queries

问题

I'm trying to run the following bit of code, but the comparison fails by not handing my the entities I expect it to.

It's comparing 06/09/2011 0:00:00 to 06/09/2011 12:25:00, the latter being my databases record value. So that's why the comparison is failing and I'm not getting the records I need.

I'm just trying to compare if the dates match up, I'm don't care about the time.

DateTime today = DateTime.Now.Date;
var newAuctionsResults = repo.FindAllAuctions()
                        .Where(a => a.IsActive == true || a.StartTime.Value == today)
                        .ToList();

How can I compare only the dates?

If use the .Date property in the .StartTime.Value part, I get an exception:

The specified type member 'Date' is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported.

回答1:

You can use the individual members:

var newAuctionsResults = repo.FindAllAuctions()
                        .Where(a => a.IsActive == true 
                                    || (a.StartTime.Value.Year == todayYear
                                        && a.StartTime.Value.Month == todayMonth
                                        && a.StartTime.Value.Day == todayDay))
                        .ToList();

...or use any of the other methods/properties supported in L2E.

回答2:

You can also use EntityFunctions.TruncateTime() under the namespace System.Data.Objects

Ex.

db.Orders.Where(i => EntityFunctions.TruncateTime(i.OrderFinishDate) == EntityFunctions.TruncateTime(dtBillDate) && i.Status == "B")

Works like charm.

回答3:

try

DateTime todayStart = DateTime.Now.Date;
DateTime todayEnd = DateTime.Now;
var newAuctionsResults = repo.FindAllAuctions()
                        .Where(a => a.IsActive == true || (a.StartTime.Value >= todayStart && a.StartTime.Value <= todayEnd))
                        .ToList();

回答4:

You could convert using

DateTime.ToShortDateString()

http://msdn.microsoft.com/en-us/library/system.datetime.toshortdatestring.aspx

This would neglect the Time.

Then compare the two Strings.

if(string1 == string2)
{
 //Do Something
}

来源：https://stackoverflow.com/questions/7320608/simple-way-to-compare-dates-in-datetime-attribute-using-entity-framework-4-and-l

标签

datetime

entity-framework-4