数据源是无效类型。它必须是 IListSource、IEnumerable 或 IDataSource

Question

为大学导师建立一个调度系统。我编写了一个在单击按钮时运行的 LINQ 查询，我想在 gridview 中返回可用的插槽。因为查询返回匿名类型，所以数据绑定在标题中抛出错误。我已经在这里寻找修复方法，但查询在控件（此处的按钮）内没有任何内容，所以我不确定如何进行更改。

表格：

CREATE TABLE [dbo].[Sessions] (
[sessionID]              INT           IDENTITY (1, 1) NOT NULL,
[create_date]            DATETIME      NOT NULL,
[last_update_date]       DATETIME      NOT NULL,
[tutorCWID]              INT           NOT NULL,
[semesterID]             INT           NOT NULL,
[session_date]           DATE          NOT NULL,
[session_start_time]     TIME (7)      NOT NULL,
[session_end_time]       NCHAR (10)    NOT NULL,
[session_bookings]       INT           NOT NULL,
[session_group_size]     INT           NOT NULL,
[session_student_report] VARCHAR (500) NULL,
[session_tutor_report]   VARCHAR (500) NULL,
[session_documents]      VARCHAR (100) NULL,
CONSTRAINT [PK_Session] PRIMARY KEY CLUSTERED ([sessionID] ASC),
CONSTRAINT [FK_Session_UserProfileTutor] FOREIGN KEY ([tutorCWID])            REFERENCES [dbo].[UserProfiles] ([userCWID]),
CONSTRAINT [FK_Session_Semester] FOREIGN KEY ([semesterID]) REFERENCES     [dbo].[Semesters] ([semesterID]));

CREATE TABLE [dbo].[UserProfiles] (
[userCWID]     INT           NOT NULL,
[first_name]   VARCHAR (50)  NOT NULL,
[last_name]    VARCHAR (50)  NOT NULL,
[email]        VARCHAR (150) NOT NULL,
[phone_mobile] NUMERIC (18)  NULL,
[phone_work]   NUMERIC (18)  NULL,
[status]       NCHAR (10)    NOT NULL,
[password]     VARCHAR (50)  NOT NULL,
[user_typeID]  INT           NOT NULL,
[ImareUrl]     VARCHAR (50)  NULL,
CONSTRAINT [PK_Tutor] PRIMARY KEY CLUSTERED ([userCWID] ASC),
CONSTRAINT [FK_UserProfile_UserType] FOREIGN KEY ([user_typeID]) REFERENCES [dbo].[UserTypes] ([user_typeID]));

CREATE TABLE [dbo].[UserProfiles_Courses] (
[tutorCWID] INT            NOT NULL,
[courseID]  VARCHAR (50)   NOT NULL,
[note]      NVARCHAR (100) NULL,
CONSTRAINT [PK_UserProfiles_Courses] PRIMARY KEY CLUSTERED ([tutorCWID] ASC, [courseID] ASC),
CONSTRAINT [FK_UserProfiles_Courses_Courses] FOREIGN KEY ([courseID]) REFERENCES [dbo].[Courses] ([courseID]),
CONSTRAINT [FK_UserProfiles_Courses_UserProfiles] FOREIGN KEY ([tutorCWID]) REFERENCES [dbo].[UserProfiles] ([userCWID]));

ASP.NET 代码隐藏：

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

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

string _StdSessCourse = "";
DateTime _StdSessDate = DateTime.Now;
string _semester = "";
protected void Page_Load(object sender, EventArgs e)
{

}
protected void btnStdSessSearch_Click(object sender, EventArgs e)
{
    _StdSessCourse = ddlStdSessCourse.SelectedValue;
    _StdSessDate = calStdSessDate.SelectedDate;


    using (ISDS411_FinalProjectDB_5Entities stdSessEntity = new ISDS411_FinalProjectDB_5Entities())
    {
        var stdSessAvailable = (from s in stdSessEntity.Sessions
                                join up in stdSessEntity.UserProfiles on s.tutorCWID equals up.userCWID
                                join uc in stdSessEntity.UserProfiles_Courses on up.userCWID equals uc.tutorCWID
                                where uc.courseID == _StdSessCourse && s.session_date == _StdSessDate
                                orderby s.session_date
                                select new
                                {
                                    up.first_name,
                                    up.last_name,
                                    s.session_start_time,
                                    s.session_end_time,
                                    s.session_group_size,
                                    s.session_bookings,
                                }).FirstOrDefault();

        gvStdSessAvailable.DataSource = stdSessAvailable;
        gvStdSessAvailable.DataBind();
    }
  }
}

这是网格视图：

<%@ Page Title="Student - Select Tutoring Session" Language="C#" MasterPageFile="~/Students/StudentMasterPage.master" AutoEventWireup="true" CodeFile="StudentSelectSession.aspx.cs" Inherits="Students_StudentSelectSession" %>

<asp:Content ID="Content1" ContentPlaceHolderID="cpMainContent" Runat="Server">
<h1>Select a session</h1>
<p>Use the controls below to select a tutoring session:
    <ol>
        <li>Select the course you want to be tutored in from the dropdown menu.</li>
        <li>Select the date that you are looking for a tutoring session on.</li>
        <li>Click the "Search" button.</li>
    </ol>
</p>
<table>
    <tr>
        <td>
            <asp:DropDownList ID="ddlStdSessCourse" runat="server" AutoPostBack="True" DataSourceID="SqlDataSource2" DataTextField="courseID" DataValueField="courseID"></asp:DropDownList>
            <asp:SqlDataSource ID="SqlDataSource2" runat="server" ConnectionString="<%$ ConnectionStrings:ISDS411_FinalProjectDB_5ConnectionString1 %>" SelectCommand="SELECT [courseID] FROM [Courses]"></asp:SqlDataSource>
        </td>
    </tr>
    <tr>
        <td>
            <asp:Calendar ID="calStdSessDate" runat="server"></asp:Calendar>
        </td>
    </tr>
    <tr>
        <td>
            <asp:Button ID="btnStdSessSearch" runat="server" Text="Search" OnClick="btnStdSessSearch_Click" />
        </td>
    </tr>
    <tr>
        <td>
            <asp:GridView ID="gvStdSessAvailable" runat="server" DataKeyNames="sessionID" EmptyDataText="There are no data records to display." AllowPaging="True" AllowSorting="True"></asp:GridView>
        </td>
    </tr>
</table>
<p><a href="~/Students/StudentHome.aspx" runat="server">Go back to Student Homepage</a></p>

我想这需要匿名类型以外的其他东西，但不知道如何将它们组合在一起。或者，我不能使用网格视图，但我想利用“选择”功能让学生选择他们想要的辅导课程。

Answer 1

尝试更改：.FirstOrDefault(); 到 .AsEnumerable();

“我想这需要匿名类型以外的东西，但不知道如何组合起来” 只需创建一个具有属性的新类并像这样使用它：

var stdSessAvailable = (from s in stdSessEntity.Sessions
                            join up in stdSessEntity.UserProfiles on s.tutorCWID equals up.userCWID
                            join uc in stdSessEntity.UserProfiles_Courses on up.userCWID equals uc.tutorCWID
                            where uc.courseID == _StdSessCourse && s.session_date == _StdSessDate
                            orderby s.session_date
                            select new SessAvailable
                            {
                               FirstName = up.first_name,
                               LastName = up.last_name,
                               SessionStarTime = s.session_start_time,
                               SessionEndTime = s.session_end_time,
                               SessionGroupSize = s.session_group_size,
                               SessionBookings = s.session_bookings,
                            }).AsEnumerable();