Question

我创建了 EF 4 ＆amp; C＃获取一些数据。我正在使用Linq。其内容如下：

    public List<object> GenerateCallTrackingReport(int startRowIndex, int maximumRows, int createdByID)
    {
        var query = from c in this.ObjectContext.CallLogs                        
                    select new
                    {
                        CallLogID = c.CallLogID,
                        DomainName = c.CallDomain.FullName,
                        CreatedByID = c.CreatedByID,
                        CreatedBy = c.CreatedByUser.FirstName + " " + c.CreatedByUser.LastAccessIPN,
                        CalledOn = c.CallDate,
                        IssueResolutionTime = c.IssueResolutionTime,                            
                        CallType = c.CallType.FullName,
                        CallDescription = c.CallDescription,
                        CustomerName = (c.CustomerID > 0 ? c.Customer.FirstName + " " + c.Customer.LastAccessIPN : c.TempCaller.FirstName + " " + c.TempCaller.LastName),
                        CustomerEmail = (c.CustomerID > 0 ? c.Customer.Email : string.Empty),
                        CustomerResponse = c.Response.FullName,
                        IsPending = c.IsPending,
                        NeedFurtherContact = c.NeedFurtherContact
                    };

        if (createdByID > 0)
            query = query.Where(c => c.CreatedByID == createdByID);

        if (maximumRows > 0)
            query = query.Skip(startRowIndex).Take(maximumRows);

        return query.ToList<object>();

    }

这导致以下错误：

Unable to cast the type 'System.Int64' to type 'System.Object'. LINQ to Entities only supports casting Entity Data Model primitive types.

任何想法我是否收到此错误？

由于

Answer 1

解决

我有两个问题，每个问题都会导致此错误：

<强> 1 即可。我正在访问 NULLABLE 实体属性，而不检查它们是否有值。说 CustomerID 是 NULLABLE ，所以我的查询变成了这样的东西！

    var query = from c in this.ObjectContext.CallLogs                        
                select new
                {
                    CallDescription = c.CallDescription,
                    CustomerID = c.CustomerID.HasValue ? c.CustomerID.Value : 0,
                    CustomerName = c.CustomerID.HasValue ? c.Customer.Name : ""
                };

    if (maximumRows > 0)
        query = query.Skip(startRowIndex).Take(maximumRows);

    return query.ToList<object>();

因此，在访问它之前，只需通过 HasValue 属性检查任何空值（选择部分中的第二行）。

<强> 2 即可。我还试图在select语句中将整数转换为字符串。所以我只是决定用HTML转换而不是直接在这里进行转换。这解决了我的问题。

希望这有助于某人！

Answer 2

进入ToList电话后，您希望在C＃中执行此操作，而不是在数据库中执行。使用AsEnumerable作为一种说法，“停止在数据库中执行此操作，在C＃中执行此操作。”

在最后ToList之前添加，以便在数据库上完成所有其他操作。

Answer 3

首先，我不会检索整个表，然后在C＃中对完整数据集进行查询。将linq链接到像这样的实体方法会使它变得更快 - 当你获得庞大的数据集时会大大增加：

this.ObjectContext.CallLogs
    .Where(c => c.CreatedByID == createdByID)
    .Skip(startRowIndex)
    .Take(maximumRows)
    .Select(new
        {
                        CallLogID = c.CallLogID,
                        DomainName = c.CallDomain.FullName,
                        CreatedByID = c.CreatedByID,
                        CreatedBy = c.CreatedByUser.FirstName + " " + c.CreatedByUser.LastAccessIPN,
                        CalledOn = c.CallDate,
                        IssueResolutionTime = c.IssueResolutionTime,                            
                        CallType = c.CallType.FullName,
                        CallDescription = c.CallDescription,
                        CustomerName = (c.CustomerID > 0 ? c.Customer.FirstName + " " + c.Customer.LastAccessIPN : c.TempCaller.FirstName + " " + c.TempCaller.LastName),
                        CustomerEmail = (c.CustomerID > 0 ? c.Customer.Email : string.Empty),
                        CustomerResponse = c.Response.FullName,
                        IsPending = c.IsPending,
                        NeedFurtherContact = c.NeedFurtherContact
        })
    .ToList();

其次，我不知道确切的问题，但创建像这样的动态对象列表并不是一个好主意。创建一个CallLogModel类，其中包含您要放入对象的属性，如下所示：

.Select(new CallLogModel
        {
                        CallLogID = c.CallLogID,
                        DomainName = c.CallDomain.FullName,
                        CreatedByID = c.CreatedByID,
                        CreatedBy = c.CreatedByUser.FirstName + " " + c.CreatedByUser.LastAccessIPN,
                        CalledOn = c.CallDate,
                        IssueResolutionTime = c.IssueResolutionTime,                            
                        CallType = c.CallType.FullName,
                        CallDescription = c.CallDescription,
                        CustomerName = (c.CustomerID > 0 ? c.Customer.FirstName + " " + c.Customer.LastAccessIPN : c.TempCaller.FirstName + " " + c.TempCaller.LastName),
                        CustomerEmail = (c.CustomerID > 0 ? c.Customer.Email : string.Empty),
                        CustomerResponse = c.Response.FullName,
                        IsPending = c.IsPending,
                        NeedFurtherContact = c.NeedFurtherContact
        })

无法将类型“System.Int64”强制转换为“System.Object”类型。 LINQ to Entities仅支持转换实体数据模型基元类型

3 个答案:

解决