将十进制的linq结果转换为ObservableCollection <string>

Question

尝试将来自LINQ查询的结果存储到ObservableCollection中，但linq的结果是十进制类型。

ObservableCollection<string> cost = 
    new ObservableCollection<string>((from i in context.Items 
             where i.Cost != null 
             && i.Cost > 0 
             orderby i.Cost 
             select i.Cost).Distinct()); 

它不会编译说'The best overloaded method match for 'System.Collections.ObjectModel.ObservableCollection<string>.ObservableCollection(System.Collections.Generic.IEnumerable<string>)' has some invalid arguments.

我看着here但它并没有帮助我很多。

UPDATE

我曾尝试没有成功如下：

ObservableCollection<string> cost = 
new ObservableCollection<string>((from i in context.Items 
            where i.Cost != null 
            && i.Cost > 0 
            orderby i.Cost 
            select i.Cost).Distinct() 
               .Select(i=>i.ToString())); 

和

ObservableCollection<string> cost = 
new ObservableCollection<string>((from i in context.Items 
            where i.Cost != null 
            && i.Cost > 0 
            orderby i.Cost 
            select i.Cost.ToString()).Distinct()); 

当我在LINQPad同时运行，我得到以下错误：
LINQ to Entities does not recognize the method 'System.String ToString()' method, and this method cannot be translated into a store expression. Message LINQ to Entities does not recognize the method 'System.String ToString()' method, and this method cannot be translated into a store expression.

Answer 1

尝试

ObservableCollection<string> cost = 
    new ObservableCollection<string>((from i in context.Items 
             where i.Cost != null 
             && i.Cost > 0 
             orderby i.Cost 
             select i.Cost).Distinct() 
                .AsEnumerable() 
                .Select(c => c.ToString())); 

由于显然EF提供商似乎无法翻译ToString()调用到SQL，投入到AsEnumerable()一个来电，将会带给查询到内存和ToString()通话将使用LINQ到对象。

Answer 2

转换Cost到字符串ToString：

ObservableCollection<string> cost = 
    new ObservableCollection<string>((from i in context.Items 
             where i.Cost != null 
             && i.Cost > 0 
             orderby i.Cost 
             select i.Cost.ToString()).Distinct()); 

使用任何CultureInfo你的需要，如果有的话，称ToString()时。

Answer 3

为什么不使用ToString（）？

ObservableCollection<string> cost = 
    new ObservableCollection<string>((from i in context.Items 
            where i.Cost != null 
            && i.Cost > 0 
            orderby i.Cost 
            select i.Cost.ToString()).Distinct()); 

Answer 4

您应该context.Items选择字符串值铸造他们创造一个ObservableCollection<string>到String

ObservableCollection<string> cost = 
    new ObservableCollection<string>((from i in context.Items 
             where i.Cost != null 
             && i.Cost > 0 
             orderby i.Cost 
             select i.Cost.ToString()).Distinct()); 

或创建一个ObservableCollection<decimal>

ObservableCollection<decimal> cost = 
    new ObservableCollection<decimal>((from i in context.Items 
             where i.Cost != null 
             && i.Cost > 0 
             orderby i.Cost 
             select i.Cost).Distinct()); 

Answer 5

执行ToString的Distinct后。这样它就不会创建这么多的字符串，并且可以比较不同的字符串。

ObservableCollection<string> cost = 
    new ObservableCollection<string>((from i in context.Items 
             where i.Cost != null 
             && i.Cost > 0 
             orderby i.Cost 
             select i.Cost).Distinct() 
                .Select(i=>i.ToString()));