比较执行期间指定的日期时间字段的 C# 方法？

Question

我的项目有许多带有日期字段的对象，我经常需要选择一个这样的字段在日期范围内的所有内容。

例如：

public class Contract

{

    public DateTime SignDate { get; set; }

    public DateTime ReleaseDate { get; set; }

}

public class PersonalCheck

{

    public DateTime SignDate { get; set; }

    public DateTime ProcessDate { get; set; }

    public DateTime VoidDate { get; set; }

}

如果我只关心 SignDate，那会很容易。我会声明一个接口...

public interface IObjectWithSignDate

{

    DateTime SignDate { get; set; }

}

...更改我的其他对象以从它继承，然后创建一个这样的方法：

    public static IQueryable<T> SignedWithin<T>(this IQueryable<T> items, DateTime start, DateTime end) where T : IObjectWithSignDate

    {

        return items.Where(q => q.SignDate >= start && q.SignDate <= end);

    }

如何避免为 ReleaseDate、ProcessDate、VoidDate 等重写此函数？我可以让这个方法接受任何对象的 IQueryable 和一个告诉它运行这个选择器的日期字段的变量吗？

请注意，这必须能够 a) 在 LinqToEntities 中执行以针对数据库运行并且 b) 不会增加大量开销（因为我担心反射可能会这样做）

Answer 1

简单但具体您可以添加这样的扩展方法：public static class DateTimeExtensions{&nbsp; &nbsp; public static bool IsBetween(this DateTime thisDateTime, DateTime start, DateTime end)&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; return thisDateTime >= start && thisDateTime <= end;&nbsp; &nbsp; }}您可以单独进行单元测试。然后您可以在要检查的任何日期时间字段上使用它。例如：var start = new DateTime(2017, 1, 1);var end = new DateTime(2017, 12, 31, 23, 59, 59);IList<Contract> contracts = new List<Contract>(); // or anything enumerablevar contractsSignedBetween = contracts.Where(x => x.SignDate.IsBetween(start, end));var contractsReleasedBetween = contracts.Where(x => x.ReleaseDate.IsBetween(start, end));（请注意我如何将开始日期时间设置为 00:00:00 时间，将结束日期时间设置为 23:59:59 时间[也可以包括毫秒]，以便包括最后一天的时间。）使其可重用如果你发现自己需要做很多事情，你可以做一个扩展public static class EnumerableContractsExtensions{&nbsp; &nbsp; public static IEnumerable<Contract> SignedBetween(this IEnumerable<Contract> contracts, DateTime start, DateTime end)&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; return contracts.Where(x => x.SignDate.IsBetween(start, end));&nbsp; &nbsp; }}并像这样使用它&nbsp;var contractsSignedBetween = contracts.SignedBetween(start, end);也可以单独进行单元测试。更灵活但更具体使用表达式说出您想要的日期...public static class EnumerableContractsExtensions{&nbsp; &nbsp; public static IEnumerable<Contract> Between(this IEnumerable<Contract> contracts, Func<Contract, DateTime> selector, DateTime start, DateTime end)&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; return contracts.Where(x => selector(x).IsBetween(start, end));&nbsp; &nbsp; }}然后做：var contractsSignedBetween = contracts.Between(x => x.SignDate, start, end);var contractsReleasedBetween = contracts.Between(x => x.ReleaseDate, start, end);灵活通用全力以赴并通用（尽管您不能将其设为扩展方法，因为它是通用的）：public static class EnumerableExtensions{&nbsp; &nbsp; public static IEnumerable<T> Between<T>(IEnumerable<T> items, Func<T, DateTime> selector, DateTime start, DateTime end)&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; return items.Where(x => selector(x).IsBetween(start, end));&nbsp; &nbsp; }}同样，这本身就是可测试的，可以像这样使用：IList<Contract> contracts = new List<Contract>();IList<PersonalCheck> personalChecks = new List<PersonalCheck>();var contractsSignedBetween = EnumerableExtensions.Between(contracts, x => x.SignDate, start, end);var checksSignedBetween = EnumerableExtensions.Between(personalChecks, x => x.SignDate, start, end);使其可查询为了使该方法起作用，IQueryable需要转向表达式树，因为 LINQ to Entities 不知道如何将方法转换为 SQL。public static IQueryable<TSource> Between<TSource, TKey>(&nbsp; &nbsp; this IQueryable<TSource> source,&nbsp; &nbsp; Expression<Func<TSource, TKey>> keySelector,&nbsp; &nbsp; TKey low,&nbsp; &nbsp; TKey high)&nbsp; &nbsp; where TKey : IComparable<TKey>{&nbsp; &nbsp; Expression key = keySelector.Body;&nbsp; &nbsp; Expression lowerBound = Expression.LessThanOrEqual(Expression.Constant(low), key);&nbsp; &nbsp; Expression upperBound = Expression.LessThanOrEqual(key, Expression.Constant(high));&nbsp; &nbsp; Expression and = Expression.AndAlso(lowerBound, upperBound);&nbsp; &nbsp; Expression<Func<TSource, bool>> lambda =&nbsp; &nbsp; &nbsp; &nbsp; Expression.Lambda<Func<TSource, bool>>(and, keySelector.Parameters);&nbsp; &nbsp; return source.Where(lambda);}仍然会像这样使用：var contractsSignedBetween = contracts.Between(x => x.SignDate, start, end);这也适用于DateTimes以外的事物。希望这可以帮助。