c# – 如何解决此“System.Data.Entity.DynamicProxies”错误

2023年7月3日 200次阅读

我是
Linq和EF Code First的新手,遇到了一个我无法弄清楚的问题.我正在使用ASP.Net Web Forms,EF Code First和Linq开发概念验证测试程序.我的想法是我根据数据库动态生成页面的服务器控件.在没有EF的情况下,我已经构建了相同的应用程序但是希望在这个项目中学到这一点.如果我使用文字但是在数据绑定RadioButtonList时收到错误,我可以得到正确的结果.

DataBinding: 'System.Data.Entity.DynamicProxies.Choice_EA448AD48C19F54FBB6BF09B7A03BA899DBE75EC189635A8982E7C3B1D8F4ABD' does not contain a property with the name '4'.

Line 34:                 content.Controls.Add(ql);
Line 35:                 ql.DataSource = choices;
Line 36:                 ql.DataBind();            
Line 37:         }

名称为“4”的属性只是我数据库中的值.我不确定这个问题是否与延迟加载有关,或者只是缺乏适当的Linq知识但我真的很感激,如果有人可以指出我正确的方向.

这是我正在使用的三个类文件和我正在尝试构建的C#页面.请记住,我计划将数据访问分成另一个类,但只是试图让我自己的演示工作.
Exam.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.ComponentModel.DataAnnotations;

/// <summary>
/// Summary description for Exam
/// </summary>
public class Exam
{    
    public int ExamId { get; set; }

    public string Title { get; set; }

    public string Description { get; set; }

    public bool Status { get; set; }

    public DateTime DateCreated { get; set; }

    public string CreatedBy { get; set; }

    public virtual ICollection<Question> Questions { get; set; }
}

Question.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

/// <summary>
/// Summary description for Question
/// </summary>
public class Question
{
    public int QuestionId { get; set; }

    public string QuestionText { get; set; }

    public int Order { get; set; }

    public DateTime DateCreated { get; set; }

    public bool Status { get; set; }

    public string CreatedBy { get; set; }

    public string QuestionType { get; set; }

    public int ExamId { get; set; }

    public virtual Exam Exam { get; set; }

    public virtual ICollection<Choice> Choices { get; set; }
}

Choice.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

/// <summary>
/// Summary description for Choice
/// </summary>
public class Choice
{
    public int ChoiceId { get; set; }

    public string ChoiceText { get; set; }

    public int Order { get; set; }

    public bool Status { get; set; }

    public bool Correct { get; set; }

    public DateTime DateCreated { get; set; }

    public string CreatedBy { get; set; }

    public int QuestionId { get; set; }

    public virtual Question Question { get; set; }
}

Testing.aspx.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class Testing : System.Web.UI.Page
{

    protected void Page_Load(object sender, EventArgs e)
    {
        ExamsContext db = new ExamsContext();

        var questions = (from c in db.Exams
                     from q in c.Questions
                     where c.ExamId == 1
                     select q).ToList();
        ContentPlaceHolder content = (ContentPlaceHolder)this.Master.FindControl("MainContent");
        foreach (var question in questions)
        {
            Literal questionLabel = new Literal();
            questionLabel.Text = Convert.ToString(question.QuestionId) + ".&nbsp;" + question.QuestionText + "<br/>";
            content.Controls.Add(questionLabel);

            var choices = (from c in question.Choices select c).ToList();

            RadioButtonList ql = new RadioButtonList();   
                foreach (var choice in choices)
                {
                    ql.DataValueField = Convert.ToString(choice.ChoiceId);
                    ql.DataTextField = choice.ChoiceText;
                }
                content.Controls.Add(ql);
                ql.DataSource = choices;
                ql.DataBind();            
        }        
    }
}

最佳答案 我使用ASP.NET WebForms已经有一段时间了,但我认为你的问题在于：

ql.DataValueField = Convert.ToString(choice.ChoiceId);
ql.DataTextField = choice.ChoiceText;

我认为Convert.ToString(choice.ChoiceId)告诉控件使用名为“4”的属性.

试试这个：

ql.DataValueField = "ChoiceId";
ql.DataTextField = "ChoiceText";

即,您需要指定要使用的属性的名称,而不是值

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