Question

我试图从IQueryable中选择一个新对象列表。当IQueryable中的特定参数为null时，它会返回列表但该对象。

var companyName = "Company";    

var gridObjects = iQueryableObjectList.Select(obj => new GridObject
            {
                AddedByEmployeeId = obj.AddedByEmployeeId,
                AddedByEmployeeSignature = obj.AddedByEmployee.Signature,
                AddedDateTime = obj.Created,
                DocumentId = obj.DocumentId,
                ResponsibleEmployeeId = obj.ResponsibleEmployeeId,
                ResponsibleEmployee = obj.ResponsibleEmployeeId != null ? 
                    obj.ResponsibleEmployee.FirstName + " " + obj.ResponsibleEmployee.LastName :
                    companyName,
                Id = obj.Id,
                IsCompanyWide = obj.IsCompanyWide
            });

iQueryableObjectList包含6个ObjectItem类型的对象。其中一个将ResponsibleEmployeeId值设置为null。

在此select语句之后，gridObjects包含5个元素，全部来自iQueryableObjectList，但ResponsibleEmployeeId值设置为null的元素除外。

我提到ResponsibleEmployeeId在Guid?和ObjectItem这两个类中都是GridObject。

如果我删除

ResponsibleEmployeeId = obj.ResponsibleEmployeeId,
ResponsibleEmployee = obj.ResponsibleEmployeeId != null ? 
                    obj.ResponsibleEmployee.FirstName + " " + obj.ResponsibleEmployee.LastName :
                    companyName,

从该select语句中返回6个元素。

有没有人对此有所了解？如果需要，请询问其他信息。

编辑：问题解决了。在某些配置中，需要映射该实体ResponsibleEmployeeId，因此当EF看到它具有空值时，它只是忽略它。

Answer 1

尝试按obj.ResponsibleEmployeeId != null

更改代码obj.ResponsibleEmployeeId != DBNull.Value

var companyName = "Company";    

var gridObjects = iQueryableObjectList.Select(obj => new GridObject
            {
                AddedByEmployeeId = obj.AddedByEmployeeId,
                AddedByEmployeeSignature = obj.AddedByEmployee.Signature,
                AddedDateTime = obj.Created,
                DocumentId = obj.DocumentId,
                ResponsibleEmployeeId = obj.ResponsibleEmployeeId,
                ResponsibleEmployee = obj.ResponsibleEmployeeId != DBNull.Value ? 
                    obj.ResponsibleEmployee.FirstName + " " + obj.ResponsibleEmployee.LastName :
                    companyName,
                Id = obj.Id,
                IsCompanyWide = obj.IsCompanyWide
            });

Answer 2

好的，我和EF有类似的问题，当涉及到将相关实体解析为POCO时。（GridObject）在你的情况下，我不认为它会使你的源表中有一个带有ResponsibleEmployeeId的FK列的事实绊倒，你可能会仔细检查这个值是实际上是空的.. 请尝试以下方法：

var gridObjects = iQueryableObjectList.Select(obj => new GridObject {
            {
                AddedByEmployeeId = obj.AddedByEmployeeId,
                AddedByEmployeeSignature = obj.AddedByEmployee.Signature,
                AddedDateTime = obj.Created,
                DocumentId = obj.DocumentId,
                ResponsibleEmployeeId = obj.ResponsibleEmployee.EmployeeId
                ResponsibleEmployee = obj.ResponsibleEmployee != null ? obj.ReponsibleEmployee.FirstName + " " + obj.ResponsibleEmployee.LastName : companyName,
                Id = obj.Id,
                IsCompanyWide = obj.IsCompanyWide
            });

有一些＆＃34;怪癖＆＃34;到Linq2Entities，取决于已经从EF中获取iQueryableObjectList的内容，考虑到它可能还没有实现，但你也可能绊倒其中一个。当尝试使用具有潜在空实体的操作的POCO ViewModel饱和时，我有时会得到NULL引用异常和奇怪的行为。通常我的目的是让我的Queryables在尝试使POCO饱和之前使得到的实体或中间匿名类型饱和。

即。

var gridObjects = iQueryableObjectList.Select(obj => new 
            {
                AddedByEmployeeId = obj.AddedByEmployeeId,
                AddedByEmployeeSignature = obj.AddedByEmployee.Signature,
                AddedDateTime = obj.Created,
                DocumentId = obj.DocumentId,
                ResponsibleEmployeeId = obj.ResponsibleEmployeeId,
                ResponsibleEmployee = obj.ResponsibleEmployee,
                Id = obj.Id,
                IsCompanyWide = obj.IsCompanyWide
            }).ToList() // Saturates the entity data incl. Responsible Employee...
            .Select( obj => new GridObject
{
                AddedByEmployeeId = obj.AddedByEmployeeId,
                AddedByEmployeeSignature = obj.AddedByEmployee.Signature,
                AddedDateTime = obj.Created,
                DocumentId = obj.DocumentId,
                ResponsibleEmployeeId = obj.ResponsibleEmployeeId,
                ResponsibleEmployee = obj.ResponsibleEmployee != null
                  ? obj.ResponsibleEmployee.FirstName + " " + obj.ResponsibleEmployee.LastName 
                  : companyName,
                Id = obj.Id,
                IsCompanyWide = obj.IsCompanyWide
            });

对于视图模型，我们通常会公平地保持它们＃34;平坦＆＃34;相对于回来的数据。例如，在上面的示例中，我考虑使用FirstName＆amp; GridObject中的LastName列以及CompanyName具有名为DisplayName的计算属性。从Linq2EF中填充POCO的相关位将变为:(选择新的GridObject { ...

   FirstName = obj.ResponsibleEmployee.FirstName, // EF automatically handles cases where ResponsibleEmployee is Null
   LastName = obj.ResponsibleEmployee.LastName,
   CompanyName = companyName,

... 然后在GridObject中有一个DisplayName，它是根据EmployeeId和/或Name数据的可用性计算的。

从IQueryable中选择新对象返回案例中列表的一部分

2 个答案: