Question

public class Gateway : ModelBase
    {
        public int Id { get; set; }
        public int SystemGroupId { get; set; }
        public string DeviceName { get; set; }
        public string MacAddress { get; set; }
        public bool Enabled { get; set; } 
    }

public class SystemGroup : ModelBase
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }

我正在加入这两张桌子。

var Query = (from g in dbContext.Gateways 
join s in dbContext.SystemGroups on g.SystemGroupId equals s.Id
select new {
Id = g.Id,
SystemGroupId = g.SystemGroupId,
SystemGroupName = s.Name,
DeviceName = g.DeviceName,
MacAddress = g.MacAddress,
DeviceType = g.DeviceType,
Enabled = g.Enabled });

我正在使用以下代码对这些结果集进行排序。

if (sortParameter == Resources.ViewResources.Views.SystemGroup)
   Query = Query.OrderBy(x => x.SystemGroupName);
else if (sortParameter == Resources.ViewResources.Views.DeviceName)
   Query = Query.OrderBy(x => x.DeviceName);
else
   Query = Query.OrderBy(x => x.Id);

直到现在它按预期工作。最后，我想将其转换为Gateway。

return Query.Select(x => new Gateway {
 Id= x.Id, 
 SystemGroupId = x.SystemGroupId, 
 DeviceName = x.DeviceName, 
 MacAddress=x.MacAddress, 
 DeviceType= x.DeviceType, 
 Enabled= x.Enabled}).ToList();

转换为Gateway时，会抛出错误：

实体或复杂类型＆＃39; Models.Context.Gateway＆＃39;不能在LINQ to Entities查询中构造。

Answer 1

在Linq-to-Entities中，您只能投射到匿名类型或常规类。您无法投影到现有实体类型。您可以使用linq-to-objects这样

return Query.Select new {
Id= x.Id, 
SystemGroupId = x.SystemGroupId, 
DeviceName = x.DeviceName, 
MacAddress=x.MacAddress, 
DeviceType= x.DeviceType, 
Enabled= x.Enabled}).AsEnumerable().Select(x => new Gateway {
        Id= x.Id, 
SystemGroupId = x.SystemGroupId, 
DeviceName = x.DeviceName, 
MacAddress=x.MacAddress, 
DeviceType= x.DeviceType, 
Enabled= x.Enabled}).ToList();

我没有测试过这个，请在尝试这个之后做评论。然后我可以帮助你得到答案。

如何在LINQ to Entities查询中将复杂查询转换为Model

1 个答案: