如何在EF查询中执行日期比较？

Question

请帮忙.我试图弄清楚如何在linq查询中使用DATE或DATETIME进行比较.

示例:如果我想要在今天之前启动的所有员工姓名,我会在SQL中执行以下操作:

SELECT EmployeeNameColumn
FROM EmployeeTable
WHERE StartDateColumn.Date <= GETDATE() //Today

但是linq怎么样？

DateTime startDT = //Today

var EmployeeName =  
from e in db.employee
where e.StartDateColumn <= startDT 

上面的WHERE不起作用:

异常详细信息:System.NotSupportedException:LINQ to Entities中不支持指定的类型成员"Date".仅支持初始值设定项,实体成员和实体导航属性.

Answer 1

使用该类DbFunctions修剪时间部分.

using System.Data.Entity;

var bla = (from log in context.Contacts
           where DbFunctions.TruncateTime(log.ModifiedDate) 
                              ==  DbFunctions.TruncateTime(today.Date)
           select log).FirstOrDefault();

来源:http://social.msdn.microsoft.com/Forums/en-US/csharpgeneral/thread/84d4e18b-7545-419b-9826-53ff1a0e2a62/

Answer 2

这应该工作.您确定查询的其他部分没有触发异常吗？我有几个表单查询实例

var query = from e in db.MyTable
            where e.AsOfDate <= DateTime.Now.Date
            select e;

在我的代码中.

Answer 3

这可能是由于数据库中的日期可以为空.试试这个:

var EmployeeName =
from e in db.employee
where e.StartDateColumn.Value <= startDT 

Answer 4

你可以检查这样的情况

var nextDay = DateTime.Today.AddDays(1);

var query = from e in db.MyTable
            where e.AsOfDate >= DateTime.Today && e.AsOfDate < nextDay 
            select e;

在今天(00:00:00)和tommorow(00:00:00)之间检查时,您将获得AsOfDate日期的记录,我们将获得今天的日期记录...

Answer 5

你不能使用.Date

如果您想今天查看,可以立即创建日期时间

DateTime myDate = new DateTime(DateTime.Now.Year, DateTime.Now.Month, DateTime.Now.Day);
var e = (from mds in myEntities.Table
         where mds.CreateDateTime >= myDate
         select mds).FirstOrDefault();