blocks|key|173390|text|我认为这个系统类中缺少using+System.Linq;。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|173391|并将using+System.Data.Entity;添加到代码中|173392|entityMap^0|B|I|0|2|P|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|P|8|@]|D|@]|E|$]]]|I|$]]

I think you are missing <code>using System.Linq;</code> from this system class.

and also add <code>using System.Data.Entity;</code> to the code

blocks|key|2990465|text|在我的例子中，我必须添加using+System.Data.Entity;|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2990466|entityMap^0|C|P|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

In my case, I had to add <code>using System.Data.Entity;</code>

blocks|key|2990502|text|我用它解决了我的案子|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2990503|@Html.DropDownList(model+=>+model.TypeId+...)++|code-block|syntax|javascript|2990504|使用|2990505|@Html.DropDownListFor(model+=>+model.TypeId+...)+|2990506|将会解决这个问题|2990507|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

My case it solved i was using 

<pre><code>@Html.DropDownList(model =&gt; model.TypeId ...) 
</code></pre>

using

<pre><code>@Html.DropDownListFor(model =&gt; model.TypeId ...) 
</code></pre>

will solve it

blocks|key|2777922|text|如果这与其他用户声明的缺少using指令无关，那么如果您的查询存在另一个问题，也会发生这种情况。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2777923|看看VS编译器错误列表:例如，如果查询中的"Value“变量不存在，则会出现"lambda+to+string”错误，以及一个又一个与未知/错误字段相关的错误。|2777924|在您的情况下，它可能是：|2777925|objContentLine+=+(from+q+in+db.qryContents
++++++++++++++++++where+q.LineID+==+Value
++++++++++++++++++orderby+q.RowID+descending
++++++++++++++++++select+q).FirstOrDefault();|code-block|syntax|javascript|2777926|错误：|2777927|2777928|错误241无法将lambda表达式转换为类型“string”，因为它不是委托类型|blockquote|2777929|2777930|错误242委托'System.Func<..>‘不接受%251参数|2777931|错误243名称'Value‘在当前上下文中不存在|2777932|2777933|修复"Value“变量错误，其他错误也会消失。|2777934|entityMap^0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|11|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|12|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|13|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|14|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|15|8|@]|9|@]|A|$]]|$1|N|3|O|5|P|7|16|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|17|8|@]|9|@]|A|$]]|$1|R|3|S|5|6|7|18|8|@]|9|@]|A|$]]|$1|T|3|U|5|6|7|19|8|@]|9|@]|A|$]]|$1|V|3|-4|5|6|7|1A|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|1B|8|@]|9|@]|A|$]]|$1|Y|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]]|Z|$]]

If it's not related to missing using directives stated by other users, this will also happen if there is another problem with your query.
Take a look on VS compiler error list :
For example, if the &quot;Value&quot; variable in your query doesn't exist, you will have the &quot;lambda to string&quot; error, and a few errors after another one more related to the unknown/erroneous field.
In your case it could be :
<pre><code>objContentLine = (from q in db.qryContents
 where q.LineID == Value
 orderby q.RowID descending
 select q).FirstOrDefault();
</code></pre>
Errors:
<blockquote>
Error 241 Cannot convert lambda expression to type 'string' because it is not a delegate type
Error 242 Delegate 'System.Func&lt;..&gt;' does not take 1 arguments
Error 243 The name 'Value' does not exist in the current context
</blockquote>
Fix the &quot;Value&quot; variable error and the other errors will also disappear.

blocks|key|2990480|text|对于刚刚发现这一点的人，我解决了这种类型的错误，该错误是在正确放置所有引用和using语句的情况下抛出的。显然，在返回DataTable而不是在声明的DataTable上调用它的函数中进行替换存在一些混淆。例如：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2990481|这对我很有效：|2990482|DataTable+dt+=+SomeObject.ReturnsDataTable();

List<string>+ls+=+dt.AsEnumerable().Select(dr+=>+dr["name"].ToString()).ToList<string>();|code-block|syntax|javascript|2990483|但这并没有：|2990484|List<string>+ls+=+SomeObject.ReturnsDataTable().AsEnumerable().Select(dr+=>+dr["name"].ToString()).ToList<string>();|2990485|我仍然不是100%25确定原因，但如果有人对这种类型的错误感到沮丧，请尝试一下。|2990486|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|T|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|V|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

For people just stumbling upon this now, I resolved an error of this type that was thrown with all the references and using statements placed properly. There's evidently some confusion with substituting in a function that returns DataTable instead of calling it on a declared DataTable. For example:

This worked for me:

<pre><code>DataTable dt = SomeObject.ReturnsDataTable();

List&lt;string&gt; ls = dt.AsEnumerable().Select(dr =&gt; dr["name"].ToString()).ToList&lt;string&gt;();
</code></pre>

But this didn't:

<pre><code>List&lt;string&gt; ls = SomeObject.ReturnsDataTable().AsEnumerable().Select(dr =&gt; dr["name"].ToString()).ToList&lt;string&gt;();
</code></pre>

I'm still not 100% sure why, but if anyone is frustrated by an error of this type, give this a try.

I am using a LINQ lambda expression like so: 

<pre><code>int Value = 1;
qryContent objContentLine;

using (Entities db = new Entities())
{
 objContentLine = (from q in db.qryContents
 where q.LineID == Value
 orderby q.RowID descending
 select q).FirstOrDefault();
}
</code></pre>

However, I am getting the following error:

<blockquote>
 Cannot convert lambda expression to type 'string' because it is not a delegate type
</blockquote>

Cannot convert lambda expression to type 'string' because it is not a delegate type

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋 

腾讯云代码助手

CODING DevOps

Cloud Studio

SDK中心

API中心

命令行工具

我使用LINQ lambda表达式，如下所示：int Value = 1;qryContent objContentLine;using (Entities db = new Entities()){    objContentLine = (from q in db.qryContents                      where q.LineID == Value         

问无法将lambda表达式转换为类型“string”，因为它不是委托类型
EN

回答 5

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问无法将lambda表达式转换为类型“string”，因为它不是委托类型EN

回答 5

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问无法将lambda表达式转换为类型“string”，因为它不是委托类型
EN