无法隐式转换类型'System.Collections.Generic.List< T>'以“System.Linq.IQueryable< T>' [英] Cannot implicitly convert type 'System.Collections.Generic.List<T>' to 'System.Linq.IQueryable<T>'

问题描述

我想在我的域名服务（VS 2010 Silverlight业务应用程序），返回从出来作为一个特定的值检查读数结果来创建一个查询，我的数据库设置为：

 位置
A）检查
B）InspectionItems 
C）InspectionReadings 
A）地区
B）检查
C）InspectionItems 
D）InspectionReadings 
  

所以，你可以看到，有检查读数根据区域和地点的位置。我有一个POCO叫名字StatusList：

 公共类StatusList 
 {
 [关键] 
〔编辑（假）] 
公众的Guid ID {搞定;组; } 
 
公共字符串LOCATIONNAME {搞定;组; } 
 
公众的DateTime LastInspectionDate {搞定;组; } 
 
公共字符串状态{搞定;组; } 
} 
  

而我使用返回查询的结果：

 公开的IQueryable< StatusList> GetLocationStatus（）
 {
 VAR状态=（从this.ObjectContext.Locations 
位置，location.InspectionReadings.Status ==价值
排序依据a.DateTaken 
选择新LocationStatusList（）
 {
 ID = a.ID，
 LOCATIONNAME = d.Name，
}）了ToList< StatusList>（）; 
返回状态; 
} 
  

不幸的是，返回错误的标题，我不知道为什么作为名单显然是一个列表项，我已经转换的结果。

  .ToList< LocationStatusList> 
  

解决方案

问题恰恰的，因为你叫了ToList（）。你已经宣布你返回的IQueryable< LocationStatusList> 和列表< T> 不执行的IQueryable< T>

选项（任选其一）：

• 删除了ToList 呼叫


• 更改返回类型为的IEnumerable< ; LocationStatusList> ，的IList< LocationStatusList> 或可能列表< LocationStatusList>



• 呼叫 AsQueryable已（）在了ToList（）：

    ...像以前那样... 
   .ToList（）AsQueryable已（）。 
    

请注意，你并不需要的类型在了ToList 调用的参数 - 这是同一个编译器会推断反正

。

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:

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:

    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:

    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

.ToList<LocationStatusList>

解决方案

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

Options (pick one):

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

• Call AsQueryable() after ToList():

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

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

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