使用 MVC 3 中的实体框架 4 更新相关数据 - ContosoUniversity

Question

在 ContosoUniversity 示例中来自 http://www.asp.net/entity-framework/tutorials/creating-an-entity-framework-data-model-for-an-asp-net-mvc-application 如何在学生/详细信息页面中显示每个学生的所有教师。我认为我需要通过以下实体才能获取讲师的数据：

学生（注册）

注册（课程）

课程（讲师）

讲师（课程）

我尝试使用“讲师”选项卡中的示例，但是当我必须为所有讲师准备实体时，我遇到了困难。

我创建了一个视图模型：

使用系统；

使用 System.Collections.Generic；

使用 ContosoUniversity.Models；

命名空间 ContosoUniversity.ViewModels

{

public class StudentIndexData

{

    public IEnumerable<Student> Students { get; set; }

    public IEnumerable<Enrollment> Enrollments { get; set; }

    public IEnumerable<Course> Courses { get; set; } 

    public IEnumerable<Instructor> Instructors { get; set; }

}

}

然后我从 StudentController 中的以下新的 MoreDetails 页面开始

public ActionResult MoreDetails(System.Int32?iStID)

    {
        var viewModel = new StudentIndexData();
        viewModel.Students = ctxDB.ctxStudents
        .Include(i => i.Enrollments.Select(c => c.Course))
        .Where(i => i.StudentID == iStID);



        if (iStID != null)
        {
            ViewBag.StudentID = iStID;

            viewModel.Enrollments = viewModel.Students.Where(i => i.StudentID == iStID).Single().Enrollments;
        }

        HERE IS WHERE I GET STUCK I DO NOT KNOW HOW TO POPULATE THE INSTRUCTORS ENTITY. AND COURSES ALSO.

        return View(viewModel);
    }

提前感谢您的帮助。

Answer 1

试试这个代码：

var std = db.Students
            .Include(s => s.Enrollments.Select(en=>en.Course))
            .Where(s => s.StudentId == id)
            .SingleOrDefault(); // or ToList() if you want fetch all students

if(std != null){

    // do your work, for example, accessing this properties:
    var a = std; // the student
    var b = std.Enrollments; // student's enrollments
    var c = std.Enrollments.First().Course; // test for access one of the enrollments's course
    var d = c.Instructors; // test for access course's instructors all

    // or project all instructors in a List:
    var instructors = new List<Instructor>();
    foreach (var enr in std.Enrollments) {
        foreach (var ins in enr.Course.Instructors) {
            if (!instructors.Contains(ins)) {
                instructors.Add(ins);
            }
         }
     } // now, the "instructors" contains all instructors associated with current user!

}else{
    // if is null, do something else
}

问候

更新

如果您想测试查询，请将第一行替换为这一行：

var stdquery = db.Students
                 .Include(s => s.Enrollments.Select(en=>en.Course))
                 .Where(s => s.PersonID == id);
var std = stdquery.SingleOrDefault();

你会在 stdquery 上看到这条 sql 语句：

{SELECT 
[Project1].[PersonID] AS [PersonID], 
[Project1].[C1] AS [C1], 
[Project1].[LastName] AS [LastName], 
[Project1].[FirstName] AS [FirstName], 
[Project1].[EnrollmentDate] AS [EnrollmentDate], 
[Project1].[C2] AS [C2], 
[Project1].[EnrollmentID] AS [EnrollmentID], 
[Project1].[CourseID] AS [CourseID], 
[Project1].[PersonID1] AS [PersonID1], 
[Project1].[Grade] AS [Grade], 
[Project1].[CourseID1] AS [CourseID1], 
[Project1].[Title] AS [Title], 
[Project1].[Credits] AS [Credits], 
[Project1].[DepartmentID] AS [DepartmentID]
FROM ( SELECT 
    [Extent1].[PersonID] AS [PersonID], 
    [Extent1].[LastName] AS [LastName], 
    [Extent1].[FirstName] AS [FirstName], 
    [Extent1].[EnrollmentDate] AS [EnrollmentDate], 
    '0X0X' AS [C1], 
    [Join1].[EnrollmentID] AS [EnrollmentID], 
    [Join1].[CourseID1] AS [CourseID], 
    [Join1].[PersonID] AS [PersonID1], 
    [Join1].[Grade] AS [Grade], 
    [Join1].[CourseID2] AS [CourseID1], 
    [Join1].[Title] AS [Title], 
    [Join1].[Credits] AS [Credits], 
    [Join1].[DepartmentID] AS [DepartmentID], 
    CASE WHEN ([Join1].[EnrollmentID] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C2]
    FROM  [dbo].[People] AS [Extent1]
    LEFT OUTER JOIN  (SELECT [Extent2].[EnrollmentID] AS [EnrollmentID], [Extent2].[CourseID] AS [CourseID1], [Extent2].[PersonID] AS [PersonID], [Extent2].[Grade] AS [Grade], [Extent3].[CourseID] AS [CourseID2], [Extent3].[Title] AS [Title], [Extent3].[Credits] AS [Credits], [Extent3].[DepartmentID] AS [DepartmentID]
        FROM  [dbo].[Enrollments] AS [Extent2]
        INNER JOIN [dbo].[Courses] AS [Extent3] ON [Extent2].[CourseID] = [Extent3].[CourseID] ) AS [Join1] ON [Extent1].[PersonID] = [Join1].[PersonID]
    WHERE ([Extent1].[Discriminator] = 'Student') AND ([Extent1].[PersonID] = @p__linq__0)
)  AS [Project1]
ORDER BY [Project1].[PersonID] ASC, [Project1].[C2] ASC}