[英]LINQ Group by error: “does not contain a definition for 'GroupBy'”
[英]Does Not Contain Definition for GroupBy
public struct CardGrouping
{
public string Name { get; set; }
public int Count { get; set; }
}
public List<CardGrouping> GetCardGrouping(IQueryable<Areas.RetailShop.Models.FPSinformation> queryable, Expression<Func<Areas.RetailShop.Models.FPSinformation, string>> groupingFunction)
{
return queryable.GroupBy(groupingFunction)
.Where(x => x.Key != null)
.Select(x => new CardGrouping
{
Name = x.Key,
Count = x.Sum(groupingFunction)
}).ToList();
}
我正在尝试做这样的事情,但出现错误
IQueryable<FPSinformation>
不包含'GroupBy'的定义,并且最佳扩展方法重载ParallelEnumerable.GroupBy<string, int>(ParallelQuery<string>, Func<string, int>)
需要类型为ParallelQuery<string>
的接收器
我做错了什么?
编辑
var data1 = fpslist.GroupBy(x => x.Ration_Card_Type1)
.Select(x => new
{
CardType_Name = x.Key,
CardType_Count = x.Sum(y => y.Ration_Card_Count1)
}).ToList();
这是我要优化的实际代码
有趣地将字符串更改为Areas.RetailShop.Models.FPSinformation
public List<CardGrouping> GetCardGrouping(List<Areas.RetailShop.Models.FPSinformation> queryable,
Expression<Func<Areas.RetailShop.Models.FPSinformation, string>> groupingFunction,
Func<Areas.RetailShop.Models.FPSinformation, int> sumFunction)
{
if (queryable.AsQueryable() != null)
{
var data = queryable.AsQueryable().GroupBy(groupingFunction).Where(x => x.Key != null).Select(x => new CardGrouping
{
Name = x.Key == null ? "" : x.Key.ToString(),
Count = x.Sum(sumFunction)
}).ToList();
return data;
}
return null;
}
此代码有2个问题。
首先,要使其编译, groupingFunction
应该是Func<FPSinformation, int>
-输入的类型不是string
,而是FPSinformation
。
此更改将使其进行编译,但是编译器将选择Enumerable.GroupBy
扩展方法。 所述Queryable.GroupBy
需要Expression<Func>
参数,而不是一个Func
-所以应该Expression<Func<FPSinformation, int>>
public List<CardGrouping> GetCardGrouping(IQueryable<FPSinformation> queryable,
Expression<Func<FPSinformation, int>> groupingFunction)
您将其按int
分组,因此.Where(x => x.Key != null)
没有意义x.Key
不能为null。
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