c# - 在 linq 查询中获取计数

Question

我想在 linq 查询中获取计数，它可以正常工作，无需比较 where 条件中的日期，但在比较日期后它会出现异常。

public static IList GetAllCategoryData()
{
     using (var objEntity = new BlueCouponEntities())
     {
       return (from TBL in objEntity.CategoryMasters.AsEnumerable()
                 let IIT = TBL.CategoryImageTransactions
                 select new
                 {
                 TBL.CategoryID,
                 TBL.CategoryName,
                 CategoryCount = objEntity.OfferCategoryMasters.Where(Lg => Lg.CategoryID == TBL.CategoryID && Lg.OfferMaster.EndDate > DateTime.Now.Date).Count(),
                 }
             ).ToList();
     }
}

错误是:指定的类型成员；Date； LINQ to Entities 不支持。仅支持初始值设定项、实体成员和实体导航属性。

Answer 1

您必须使用EntityFunctions.TruncateTime来获取DateTime的日期部分

using (var objEntity = new BlueCouponEntities())
{
    return (from TBL in objEntity.CategoryMasters.AsEnumerable()
                 let IIT = TBL.CategoryImageTransactions
                 select new
                 {
                 TBL.CategoryID,
                 TBL.CategoryName,
                 CategoryCount = objEntity.OfferCategoryMasters.Where(Lg => Lg.CategoryID == TBL.CategoryID && Lg.OfferMaster.EndDate > EntityFunctions.TruncateTime(DateTime.Now)).Count(),
                 }
             ).ToList();
}

由于 DateTime.Now 目前是常量，您也可以这样写

 using (var objEntity = new BlueCouponEntities())
 {
     DateTime now = DateTime.Now.Date;
     return (from TBL in objEntity.CategoryMasters.AsEnumerable()
                 let IIT = TBL.CategoryImageTransactions
                 select new
                 {
                 TBL.CategoryID,
                 TBL.CategoryName,
                 CategoryCount = objEntity.OfferCategoryMasters.Where(Lg => Lg.CategoryID == TBL.CategoryID && Lg.OfferMaster.EndDate > now).Count(),
                 }
             ).ToList();   
}