LINQ to Entities不识别方法'Int32

Question

public ActionResult ReadXMLDevices(int groupID)
{             
    var query = from k in XMLEntities.unassigneditems
    where k.DevOrAcc == true && k.Group == groupID
    select k;

    var view_query = from i in query
                     select new GetFreeDevices
                     {
                         MArticleNumber = i.ArticleNumber,
                         MFirmware = i.Firmware,
                         MGroup = i.Group,
                         MName = i.Name,
                         MSoftware = i.SoftwareVersion,
                         SA = GetNumberOfDevices(i.ArticleNumber,2),
                         STH = GetNumberOfDevices(i.ArticleNumber,3),
                         SASTH = GetNumberOfDevices(i.ArticleNumber,7)
                     };
    return PartialView(view_query);
}

public int GetNumberOfDevices(string artNo,int loc)
{
    var num_dev = (from k in XMLEntities.deviceview
                   where k.Reserved == false && k.Sold == false && k.LocationNameId == loc && k.ArticleNumber == artNo
                   select k).Count();
    return num_dev;
}

错误:

LINQ to Entities 不认识 'Int32 GetNumberOfDevices(System.String, Int32)' 方法，该方法无法转换成存储表达式。如何解决这个问题？

- Ognjen

Answer 1

您可以将查询分为两部分，以确保在调用 GetNumberOfDevices() 方法之前列表位于内存中。您可以通过将结果转换为 List 或在此情况下是 List<GetFreeDevices> 来在内存中进行查询。这样，LinQ to Entities 就不必执行任何与 XML 的翻译，并且您可以使用您的 GetNumberOfDevices() 方法。

var view_query = (from i in query
     select new GetFreeDevices
     {
        MArticleNumber = i.ArticleNumber,
        MFirmware = i.Firmware,
        MGroup = i.Group,
        MName = i.Name,
        MSoftware = i.SoftwareVersion

     }).ToList();
var result_query = from i in query
     select new GetFreeDevices
     {
        MArticleNumber = i.MArticleNumber,
        MFirmware = i.MFirmware,
        MGroup = i.MGroup,
        MName = i.MName,
        MSoftware = i.MSoftware,
        SA = GetNumberOfDevices(i.MArticleNumber,2),
        STH = GetNumberOfDevices(i.MArticleNumber,3),
        SASTH = GetNumberOfDevices(i.MArticleNumber,7)
     };
return PartialView(result_query);

请注意，最后一个语句要求PartialView接受列表或IEnumerable而不是IQueryable。

- Prutswonder

Answer 2

还有一种简单的方法。

首先，将数据从数据库加载到内存中：

// ...
var query_view = from i in query
                 select i;

query_view.Load();
// ...

然后，您可以随心所欲地使用linq-to-objects，而不是L2E：

var view_query_1 = from i in DbContext.myEntities.Local
                 select new GetFreeDevices
                 {
                     MArticleNumber = i.ArticleNumber,
                     MFirmware = i.Firmware,
                     MGroup = i.Group,
                     MName = i.Name,
                     MSoftware = i.SoftwareVersion,
                     SA = GetNumberOfDevices(i.ArticleNumber,2),   //
                     STH = GetNumberOfDevices(i.ArticleNumber,3),  // These are now ok!
                     SASTH = GetNumberOfDevices(i.ArticleNumber,7) //
                 };
    return PartialView(view_query_1.AsEnumerable());

您可以使用此技巧来处理 L2E 不支持的任何方法。

- Amin Saqi