在LINQ中获取结果函数而无需转换为存储表达式 [英] Get result function in LINQ without translate to store expression

问题描述

我需要从需要在LINQ查询中运行的函数中获取结果.此结果绑定到网格，但是在运行时我遇到此错误:

I need to get result from a function that it need to run in LINQ query. This result bind to grid but in run time I encounter with this error:

LINQ to Entities无法识别方法'System.String GetName(System.Type，System.Object)'方法，并且此方法不能为 转换为商店表达式.

LINQ to Entities does not recognize the method 'System.String GetName(System.Type, System.Object)' method, and this method cannot be translated into a store expression.

这是我的代码:

public IQueryable GetForRah_CapacityList(XQueryParam param)
{
    var result = (from x in Data()
                  select new
                  {
                      Rah_CapacityId = x.Rah_CapacityId,
                      Rah_CapacityName = x.Rah_CapacityName,
                      Rah_St = Enum.GetName(typeof(Domain.Enums.CapacityState), x.Rah_St),
                      Rah_LinesId = x.Rah_LinesId
                  }).OrderByDescending(o => new { o.Rah_CapacityId });
    return result;
}

推荐答案

您不能在Linq-To-Entities中使用此方法，因为LINQ不知道如何将Enum.GetName转换为sql.因此，使用AsEnumerable在Linq-To-Objects中在内存中执行它，并在查询后使用AsQueryable获得所需的AsQueryable:

You can't use this method in Linq-To-Entities because LINQ does not know how to translate Enum.GetName to sql. So execute it in memory with Linq-To-Objects by using AsEnumerable and after the query use AsQueryable to get the desired AsQueryable:

所以:

var result = Data()
             .OrderBy(x=> x.CapacityId)
             .AsEnumerable()
             .Select(x => new
             {
                  Rah_CapacityId = x.Rah_CapacityId,
                  Rah_CapacityName = x.Rah_CapacityName,
                  Rah_St = Enum.GetName(typeof(Domain.Enums.CapacityState), x.Rah_St),
                  Rah_LinesId = x.Rah_LinesId
             })
             .AsQueryable();

在使用AsEnumerable之前，应首先使用OrderBy，以受益于数据库排序性能. Where同样如此，请始终在AsEnumerable(或ToList)之前执行此操作.

You should first use OrderBy before you use AsEnumerable to benefit from database sorting performance. The same applies to Where, always do this before AsEnumerable(or ToList).

这篇关于在LINQ中获取结果函数而无需转换为存储表达式的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！