如何解决以下错误 [英] How to resolve below error

问题描述

如何解决



错误：表达式树可能不包含动态操作

代码：

  var  usrcat = snw.Users.Where（u = >  u.UserID == ViewBag.userid）
 .Select（u => u.Category）.SingleOrDefault（）; 
 
  var  fee = snw.FeeStructures.Where（f => f.FeeCategoryId == usrcat）
。选择（f => f.FeeAmount）.SingleOrDefault（）; 

解决方案

取出分号：

< pre lang =c＃> var fee = snw.FeeStructures.Where（f = > ; f .FeeCategoryId == usrcat）.Select（f => f.FeeAmount）.SingleOrDefault（）;

成为：

  var  fee = snw.FeeStructures.Where（f = >  f.FeeCategoryId == usrcat）。选择（f = > f.FeeAmount）.SingleOrDefault（）; 

将动态操作移到表达式树之外：

  var  userid = ViewBag.userid;  //  <  - 这是动态操作。 
 
  var  usrcat = snw.Users.Where（u = >  u.UserID == userid）
 。选择（u = >  u.Category）.SingleOrDefault（）; 
 
  var  fee = snw.FeeStructures.Where（f => f.FeeCategoryId == usrcat）
。选择（f = >  f.FeeAmount）.SingleOrDefault（）; 

NB：您使用 ViewBag 中的属性这一事实让我怀疑您是否在视图中执行数据访问代码。所有数据访问代码都属于控制器;视图应该只包含呈现响应的HTML标记所需的最小代码。

ViewBag 是动态的。因此，您需要将该值存储在某个变量中，然后对其执行操作。

  var  id = ViewBag 。用户身份; 
  var  usrcat = snw.Users.Where（u = >  u.UserID == id）.Select（u = >  u.Category）.SingleOrDefault（）; 

详情请参阅ViewBag在这里 -

MSDN [ ^ ]

CodeProject [ ^ ]



-KR

How to resolve

Error:An expression tree may not contain a dynamic operation
Code:

var usrcat = snw.Users.Where(u => u.UserID == ViewBag.userid)
                  .Select(u =>u.Category).SingleOrDefault();

 var fee = snw.FeeStructures.Where(f =>f.FeeCategoryId == usrcat)
           .Select(f =>f.FeeAmount).SingleOrDefault();

解决方案

Take out the semicolon:

var fee = snw.FeeStructures.Where(f =>; f.FeeCategoryId == usrcat).Select(f =>f.FeeAmount).SingleOrDefault();

Becomes:

var fee = snw.FeeStructures.Where(f => f.FeeCategoryId == usrcat).Select(f =>f.FeeAmount).SingleOrDefault();

Move the dynamic operation outside of the expression tree:

var userid = ViewBag.userid; // <-- This is the dynamic operation.

var usrcat = snw.Users.Where(u => u.UserID == userid)
    .Select(u => u.Category).SingleOrDefault();
 
var fee = snw.FeeStructures.Where(f =>f.FeeCategoryId == usrcat)
    .Select(f => f.FeeAmount).SingleOrDefault();

NB: The fact that you're using properties from the ViewBag makes me suspicious that you're executing data access code in the view. All data access code belongs in the controller; the view should only contain the minimum code required to render the HTML markup for the response.

ViewBag is a dynamic. Hence you need to store that value in some variable then perform operation on it.

var id = ViewBag.userid;
var usrcat = snw.Users.Where(u => u.UserID == id).Select(u => u.Category).SingleOrDefault();

Refer more about ViewBag here-
MSDN[^]
CodeProject[^]

-KR

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