Question

我需要构建一个“between”函数来检查日期是否包含在2个日期的范围内。我写了这个，但它不起作用：

private static Expression<Func<TElement, bool>> IsDateBetween<TElement>(Expression<Func<TElement, object>> valueSelector, DateTime date)
{
    var p = valueSelector.Parameters.Single();

    var after = Expression.LessThanOrEqual(
        Expression.Property(valueSelector.Body, "FromDate"), Expression.Constant(date.Date, typeof(DateTime)));

    var before = Expression.GreaterThanOrEqual(
        Expression.Property(valueSelector.Body, "ToDate"), Expression.Constant(date.Date, typeof(DateTime)));

    Expression body = Expression.And(after, before);

    return Expression.Lambda<Func<TElement, bool>>(body, p);
}

我这样称呼它：

DataContext.EventHistories.Where(IsDateBetween<EventHistory>(h => new { h.FromDate, h.ToDate }, dateInTheMiddle))

我必须使用这种方式，因为linq实体不支持日期。

由于

Answer 1

你可以尝试类似的东西

public static IQueryable<TElement> IsDateBetween<TElement>(this IQueryable<TElement> queryable, 
                                                           Expression<Func<TElement, DateTime>> fromDate, 
                                                           Expression<Func<TElement, DateTime>> toDate, 
                                                           DateTime date)
{
    var p = fromDate.Parameters.Single();
    Expression member = p;

    Expression fromExpression = Expression.Property(member, (fromDate.Body as MemberExpression).Member.Name);
    Expression toExpression = Expression.Property(member, (toDate.Body as MemberExpression).Member.Name);

    var after = Expression.LessThanOrEqual(fromExpression,
         Expression.Constant(date, typeof(DateTime)));

    var before = Expression.GreaterThanOrEqual(
        toExpression, Expression.Constant(date, typeof(DateTime)));

    Expression body = Expression.And(after, before);

    var predicate = Expression.Lambda<Func<TElement, bool>>(body, p);
    return queryable.Where(predicate);
}

使用

DataContext.EventHistories.WhereDateBetween(h =>  h.FromDate, h => h.ToDate, dateInTheMiddle));

但做起来很复杂

var myDate = DateTime.Now();

var result = DataContext.EventHistories.Where(m => m.FromDate >= myDate && m.ToDate<=myDate );

修改

好吧，要模拟DateTime.Date，你可以这样做：

var myDate = DateTime.Now.Date(); var res = histories.AsQueryable() .Where(m => EntityFunctions.CreateDateTime(m.FromDate.Year, m.FromDate.Month, m.FromDate.Day, 0, 0, 0) >= DateTime.Now && EntityFunctions.CreateDateTime(m.ToDate.Year, m.ToDate.Month, m.ToDate.Day, 0, 0, 0) <= DateTime.Now)

或创建界面

public interface IFromDateToDate { DateTime FromDate { get; set; } DateTime ToDate { get; set; } }

和扩展方法

public static IQueryable<T> WhereDatesBetween<T>(this IQueryable<T> queryable, DateTime myDate) where T : IFromDateToDate { myDate = myDate.Date; return queryable.Where(m => EntityFunctions.CreateDateTime(m.FromDate.Year, m.FromDate.Month, m.FromDate.Day, 0, 0, 0) >= myDate && EntityFunctions.CreateDateTime(m.FromDate.Year, m.FromDate.Month, m.FromDate.Day, 0, 0, 0) <= myDate); }

用法：

DataContext.EventHistories.WhereDatesBetween(dateInTheMiddle));

Answer 2

LinQ to Entities DOES支持DateTime - 我在项目中使用它并且没有问题：

var now = DateTime.Now;    
var expiredEntities = entities.Repositories.Where(repository => repository.ExpiryDate < now).ToList();

Answer 3

现在，如果我遵循这一点，你真的想写：

from item in MyTable
where FromDate <= Item.Somedate.Date 
   && Item.Somedate.Date <= ToDate
select item

但是，你不能，因为LINQ to实体不支持DateTime的Date属性。

同样，你不能写：

from item in MyTable
where FromDate <= Item.SomeDate 
   && Item.SomeDate <= ToDate
select item

因为，我认为，ToDate设置为午夜，如果Item.SomeDate有时间，则会在ToDate之后，即使它在ToDate上。

如果是这种情况，那么通常的做法就是将上限设为独占值（即首先不）部分内容）。因此：

  toDate = toDate.Date.AddDay(1);

from item in MyTable
where FromDate <= Item.SomeDate 
   && Item.SomeDate < ToDate
select item

Answer 4

为什么要烦恼所有的魔力？为什么不这样做？

if (date >= startDate and date <= endDate) {

}

表达式树，用于了解日期是否在c＃中的2个日期之间

4 个答案: