C# 无法将类型“System.Collections.Generic.List<T>”隐式转换为“System.Linq.IQueryable<T>”

Cannot implicitly convert type 'System.Collections.Generic.List<T>' to 'System.Linq.IQueryable<T>'

提问by xhedgepigx

I am trying to create a query in my domain service (VS 2010 Silverlight Business Application) that returns the results from inspection readings that came out as a specific value, my database is set up as:

我正在尝试在我的域服务（VS 2010 Silverlight 业务应用程序）中创建一个查询，该查询返回作为特定值出现的检查读数的结果，我的数据库设置为：

Locations
  a) Inspections
     b) InspectionItems
        c) InspectionReadings       
  a) Areas
     b) Inspections
        c) InspectionItems
           d) InspectionReadings

So, as you can see, there are inspection readings for locations under areas and locations. I have a POCO called name StatusList:

因此，如您所见，区域和位置下的位置有检查读数。我有一个名为 StatusList 的 POCO：

    public class StatusList
    {
        [Key]
        [Editable(false)]
        public Guid ID { get; set; }

        public string LocationName { get; set; }

        public DateTime LastInspectionDate { get; set; }

        public string Status { get; set; }
    }

which I am using to return the results of the query:

我用来返回查询结果：

    public IQueryable<StatusList> GetLocationStatus()
    {
        var status = (from location in this.ObjectContext.Locations
                      where location.InspectionReadings.Status == value
                      orderby a.DateTaken                          
                      select new LocationStatusList()
                      {
                          ID = a.ID,
                          LocationName = d.Name,                              
                      }).ToList<StatusList>();
        return status;              
    }

unfortunately, it's returning the error in the title and I have no idea why as the list is clearly a list item and i have converted the results

不幸的是，它返回了标题中的错误，我不知道为什么，因为列表显然是一个列表项，我已经转换了结果

.ToList<LocationStatusList>

采纳答案by Jon Skeet

The problem is precisely becauseyou've called ToList(). You've declared that you're returning IQueryable<LocationStatusList>, and List<T>doesn't implement IQueryable<T>.

问题正是因为您调用了ToList(). 您已经声明您要返回IQueryable<LocationStatusList>，并且List<T>没有实现IQueryable<T>.

Options (pick one):

选项（选择一项）：

• Remove the ToListcall
• Change the return type to IEnumerable<LocationStatusList>, IList<LocationStatusList>or possibly List<LocationStatusList>

• Call AsQueryable()after ToList():

  ... as before ...
  .ToList().AsQueryable();
  

• 取消ToList通话
• 将返回类型更改为IEnumerable<LocationStatusList>，IList<LocationStatusList>或者可能List<LocationStatusList>

• 调用AsQueryable()后ToList()：

  ... as before ...
  .ToList().AsQueryable();
  

Note that you don't need the type argument in the ToListcall - it's the same one that the compiler would infer anyway.

请注意，您不需要ToList调用中的类型参数- 它与编译器无论如何都会推断出的参数相同。