LINQ to Entities 无法识别转换为字符串

Question

我收到一个错误（如下），我似乎无法将我的 providerId 转换为字符串

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

我尝试转换的原因是 jQuery Datatables 抛出错误：

DataTables warning: table id=example2 - Requested unknown parameter '0' for row 0. For more information about this error, please see http://datatables.net/tn/4

代码：

var allProviders = _db.CareProviders.AsQueryable();
var resultItems = allProviders.Select(a => new
{
    ProviderId = Convert.ToString(a.ProviderId), //convert to string
    CareServiceType = a.CareServiceType,
    CareServiceName = a.CareServiceName,
    Email = a.Email
}).ToList();

Answer 1

嗯，一种典型的解决方案是按原样从数据库中获取数据，然后在您这边进行翻译：

    var allProviders = _db.CareProviders.AsQueryable();
    var resultItems = allProviders.Select(a => new
    {
        ProviderId = a.ProviderId, // fetch it as it is
        CareServiceType = a.CareServiceType,
        CareServiceName = a.CareServiceName,
        Email = a.Email
    })
    // download results from DB and execute
    // rest of the query on the application side
    .AsEnumerable()
    // now convert
    .Select(a => new
    {
        ProviderId = a.ProviderId.ToString(), //convert to string
        CareServiceType = a.CareServiceType,
        CareServiceName = a.CareServiceName,
        Email = a.Email
    });

但是，有时仅仅转换为字符串就有点矫枉过正了..

有一些转换方法实际上通常被 LINQ 理解，但这取决于您的 linq 提供程序。您可以尝试以下方法之一：

... = SqlFunctions.StringConvert(a.ProviderId)
... = Convert.ToString(a.ProviderId)
... = a.ProviderId + ""

LINQ to Entities 无法识别转换为字符串

LINQ to Entities does not recognize convert to string

c#

entity-framework

linq

tostring