C# Linq UNION 查询选择两个元素
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Linq UNION query to select two elements
提问by Leron_says_get_back_Monica
I want to select 2 elements from my database table using LINQquery and I saw an example which use UNIONI don't have much experience but I think that maybe this is what I need but I get an error which I can not fix and I'm not sure if it's fixable anyway. So here is my query:
我想使用LINQ查询从我的数据库表中选择 2 个元素，我看到了一个使用UNION我没有太多经验的例子，但我认为这可能是我需要的，但我得到一个我无法修复的错误，我是不确定它是否可以修复。所以这是我的查询：
IList<String> materialTypes = ((from tom in context.MaterialTypes
where tom.IsActive == true
select tom.Name)
.Union(from tom in context.MaterialTypes
where tom.IsActive == true
select (tom.ID))).ToList();
Which as it seems is complaining about trying to use UNIONon IQueryablewith IEnumarebale. I tried to fix that by adding ToString()like this - (tom.ID).ToStringwhich led to cleaning the error underline in Visual-Studio-2010but in runtime I get:
其中，因为它似乎在抱怨试图使用UNION上IQueryable有IEnumarebale。我试图通过这样添加来解决ToString()这个问题 -(tom.ID).ToString这导致清除错误下划线，Visual-Studio-2010但在运行时我得到：
{"LINQ to Entities does not recognize the method 'System.String ToString()' method, and this method cannot be translated into a store expression."}
Ty, Leron.
泰，勒伦。
采纳答案by Tom
EDIT:
编辑：
Ok I found why the int.ToString() in LINQtoEF fails, please read this post: Problem with converting int to string in Linq to entities
好的，我找到了 LINQtoEF 中的 int.ToString() 失败的原因，请阅读这篇文章： 在 Linq 到实体中将 int 转换为字符串的问题
This works on my side :
这对我有用：
List<string> materialTypes = (from u in result.Users
select u.LastName)
.Union(from u in result.Users
select SqlFunctions.StringConvert((double) u.UserId)).ToList();
On yours it should be like this:
在你的应该是这样的：
IList<String> materialTypes = ((from tom in context.MaterialTypes
where tom.IsActive == true
select tom.Name)
.Union(from tom in context.MaterialTypes
where tom.IsActive == true
select SqlFunctions.StringConvert((double)tom.ID))).ToList();
Thanks, i've learnt something today :)
谢谢，我今天学到了一些东西:)
