C# 存在显式转换（您是否缺少演员表？）
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An explicit conversion exists (are you missing a cast?)
提问by Aida E
I have a method that gives me the groupID of users and then I want to get the news based on the user's GroupID.
我有一种方法可以为我提供用户的 groupID，然后我想根据用户的 GroupID 获取新闻。
public IEnumerable<News> Getnews(int GroupID)
{
Expression<Func<News, bool>> constraint = null;
constraint = e => e.GroupID.Equals(GroupID);
return newsRepository.GetMany(constraint);
}
here I call the above method:
这里我调用上面的方法：
News news = newsService.Getnews(GroupID);
and this is the error :
这是错误：
Cannot implicitly convert type '
System.Collections.Generic.IEnumerable<MeetingBoard.Model.News>' to 'MeetingBoard.Model.News'. An explicit conversion exists (are you missing a cast?)
无法将类型“
System.Collections.Generic.IEnumerable<MeetingBoard.Model.News>”隐式转换为“MeetingBoard.Model.News”。存在显式转换（您是否缺少演员表？）
采纳答案by Bob Vale
Getnews returns a collection of news items, and your line is expecting a single news item.
Getnews 返回一组新闻条目，而您的线路正在等待单个新闻条目。
You could try
你可以试试
News news = newsServices.Getnews(GroupID).FirstOrDefault();
or expect an ineumerable
或者期待一个数不清的
IEnumerable<News> news = newsService.GetNews(GroupID);
回答by Paulie Waulie
This line is setting a variable which is defined as a single instance of News to an instance of IEnumerable :
这一行设置了一个变量，该变量定义为 News 的单个实例到 IEnumerable 的实例：
News news = newsService.Getnews(GroupID);
You want to change to
你想改成
IEnumerable<News> = newsService.Getnews(GroupID);
Basically you are trying to set a collection of News to a single reference of News.
基本上，您正在尝试将新闻集合设置为新闻的单个引用。
回答by Daniel Hilgarth
Getnewsreturns an IEnumerable<News>(i.e. multiple News) and you are trying to assign it to News news(i.e. a single News item). That doesn't work.
Getnews返回一个IEnumerable<News>（即多个新闻）并且您正试图将其分配给News news（即单个新闻项目）。那行不通。
There are two possibilities, depending on what you want to do.
有两种可能性，这取决于您想要做什么。
If you want to use all the news, change News newsto IEnumerable<News>:
如果要使用所有新闻，请更改News news为IEnumerable<News>：
IEnumerable<News> news = newsService.Getnews(GroupID);
If you want to use only a single news, use FirstOrDefault:
如果您只想使用单个新闻，请使用FirstOrDefault：
News news = newsService.Getnews(GroupID).FirstOrDefault();
Depending on what you expect, you also could use one of the following:
根据您的期望，您还可以使用以下方法之一：
First(): You expectGetnewsto always return at least one news. This will throw an exception if no news are returned.Single(): You expectGetnewsto always return exactly one news. This will throw an exception if more than one or zero news are returned.SingleOrDefault(): You expect zero or one news to be returned. This will throw an exception if more than one news are returned.
First(): 你期望Getnews总是至少返回一个消息。如果没有返回消息，这将引发异常。Single()：您希望Getnews始终只返回一个消息。如果返回多于一个或零个新闻，这将引发异常。SingleOrDefault()：您希望返回零个或一个消息。如果返回多个新闻，这将引发异常。
回答by MeTitus
This is what you want
这就是你想要的
IEnumerable<News> news = newsService.Getnews(GroupID);
or maybe something like:
或者可能是这样的：
News news = newsService.Getnews(GroupID).FirstOrDefault();
回答by Ahmed KRAIEM
return newsRepository.GetMany(constraint);returns an IEnumerable<News>, you should do:
return newsRepository.GetMany(constraint);返回一个IEnumerable<News>，你应该这样做：
return newsRepository.GetMany(constraint).FirstOrDefault();
return the first Newsif it is found in newRepository, null otherwise
News如果在 中找到，则返回第一个newRepository，否则为null
回答by Suraj Tiwari
An explicit conversion exists (are you missing a cast?) I was facing same problem in my C# code. I was writing code in VS. I checked full code, and I get reason behind this error. I missed 'I' in my explicit Interface name.
存在显式转换（您是否缺少强制转换？）我在 C# 代码中遇到了同样的问题。我在 VS 中编写代码。我检查了完整的代码，我明白了这个错误背后的原因。我在显式接口名称中遗漏了“I”。
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