ASP.NET Core 中的 Razor 页面和 EF Core - 更新相关数据

由 吾有佳卿 创建, 最后一次修改 2019-04-15

本教程演示如何更新相关数据。 如果遇到无法解决的问题,请下载或查看已完成的应用。 下载说明

下图显示了部分已完成页面。

课程“编辑”页 讲师”编辑”页

查看并测试“创建”和“编辑”课程页。 创建新课程。 系按其主键(一个整数)进行选择,而不是按名称。 编辑新课程。 完成测试后,请删除新课程。

创建基类以共享通用代码

“课程/创建”和“课程/编辑”页分别需要一个系名称列表。 针对“创建”和“编辑”页创建 Pages/Courses/DepartmentNamePageModel.cshtml.cs 基类:

C#

using ContosoUniversity.Data;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.EntityFrameworkCore;
using System.Linq;

namespace ContosoUniversity.Pages.Courses
{
    public class DepartmentNamePageModel : PageModel
    {
        public SelectList DepartmentNameSL { get; set; }

        public void PopulateDepartmentsDropDownList(SchoolContext _context,
            object selectedDepartment = null)
        {
            var departmentsQuery = from d in _context.Departments
                                   orderby d.Name // Sort by name.
                                   select d;

            DepartmentNameSL = new SelectList(departmentsQuery.AsNoTracking(),
                        "DepartmentID", "Name", selectedDepartment);
        }
    }
}

上面的代码创建 SelectList 以包含系名称列表。 如果指定了 selectedDepartment,可在 SelectList中选择该系。

“创建”和“编辑”页模型类将派生自 DepartmentNamePageModel。

自定义课程页

创建新的课程实体时,新实体必须与现有院系有关系。 若要在创建课程的同时添加系,则“创建”和“编辑”的基类必须包含用于选择系的下拉列表。 该下拉列表设置 Course.DepartmentID 外键 (FK) 属性。 EF Core 使用 Course.DepartmentID FK 加载 Department 导航属性。

创建课程

使用以下代码更新“创建”页模型:

C#

using ContosoUniversity.Models;
using Microsoft.AspNetCore.Mvc;
using System.Threading.Tasks;

namespace ContosoUniversity.Pages.Courses
{
    public class CreateModel : DepartmentNamePageModel
    {
        private readonly ContosoUniversity.Data.SchoolContext _context;

        public CreateModel(ContosoUniversity.Data.SchoolContext context)
        {
            _context = context;
        }

        public IActionResult OnGet()
        {
            PopulateDepartmentsDropDownList(_context);
            return Page();
        }

        [BindProperty]
        public Course Course { get; set; }

        public async Task<IActionResult> OnPostAsync()
        {
            if (!ModelState.IsValid)
            {
                return Page();
            }

            var emptyCourse = new Course();

            if (await TryUpdateModelAsync<Course>(
                 emptyCourse,
                 "course",   // Prefix for form value.
                 s => s.CourseID, s => s.DepartmentID, s => s.Title, s => s.Credits))
            {
                _context.Courses.Add(emptyCourse);
                await _context.SaveChangesAsync();
                return RedirectToPage("./Index");
            }

            // Select DepartmentID if TryUpdateModelAsync fails.
            PopulateDepartmentsDropDownList(_context, emptyCourse.DepartmentID);
            return Page();
        }
      }
}

前面的代码:

  • 派生自 DepartmentNamePageModel。
  • 使用 TryUpdateModelAsync 防止过多发布
  • 将 ViewData["DepartmentID"] 替换为 DepartmentNameSL(来自基类)。

ViewData["DepartmentID"] 将替换为强类型 DepartmentNameSL。 建议使用强类型而非弱类型。 有关详细信息,请参阅弱类型数据(ViewData 和 ViewBag)

更新“课程创建”页

使用以下标记更新 Pages/Courses/Create.cshtml:

CSHTML

@page
@model ContosoUniversity.Pages.Courses.CreateModel
@{
    ViewData["Title"] = "Create Course";
}
<h2>Create</h2>
<h4>Course</h4>
<hr />
<div class="row">
    <div class="col-md-4">
        <form method="post">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <div class="form-group">
                <label asp-for="Course.CourseID" class="control-label"></label>
                <input asp-for="Course.CourseID" class="form-control" />
                <span asp-validation-for="Course.CourseID" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Course.Title" class="control-label"></label>
                <input asp-for="Course.Title" class="form-control" />
                <span asp-validation-for="Course.Title" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Course.Credits" class="control-label"></label>
                <input asp-for="Course.Credits" class="form-control" />
                <span asp-validation-for="Course.Credits" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Course.Department" class="control-label"></label>
                <select asp-for="Course.DepartmentID" class="form-control"
                        asp-items="@Model.DepartmentNameSL">
                    <option value="">-- Select Department --</option>
                </select>
                <span asp-validation-for="Course.DepartmentID" class="text-danger" />
            </div>
            <div class="form-group">
                <input type="submit" value="Create" class="btn btn-default" />
            </div>
        </form>
    </div>
</div>
<div>
    <a asp-page="Index">Back to List</a>
</div>
@section Scripts {
    @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
}

上述标记进行以下更改:

  • 将标题从“DepartmentID”更改为“Department”。
  • 将 "ViewBag.DepartmentID" 替换为 DepartmentNameSL(来自基类)。
  • 添加“选择系”选项。 此更改将导致呈现“选择系”而不是第一个系。
  • 在未选择系时添加验证消息。

Razor 页面使用选择标记帮助器

CSHTML

<div class="form-group">
    <label asp-for="Course.Department" class="control-label"></label>
    <select asp-for="Course.DepartmentID" class="form-control"
            asp-items="@Model.DepartmentNameSL">
        <option value="">-- Select Department --</option>
    </select>
    <span asp-validation-for="Course.DepartmentID" class="text-danger" />
</div>

测试“创建”页。 “创建”页显示系名称,而不是系 ID。

更新“课程编辑”页。

使用以下代码更新“编辑”页模型:

C#

using ContosoUniversity.Models;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using System.Threading.Tasks;

namespace ContosoUniversity.Pages.Courses
{
    public class EditModel : DepartmentNamePageModel
    {
        private readonly ContosoUniversity.Data.SchoolContext _context;

        public EditModel(ContosoUniversity.Data.SchoolContext context)
        {
            _context = context;
        }

        [BindProperty]
        public Course Course { get; set; }

        public async Task<IActionResult> OnGetAsync(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            Course = await _context.Courses
                .Include(c => c.Department).FirstOrDefaultAsync(m => m.CourseID == id);

            if (Course == null)
            {
                return NotFound();
            }

            // Select current DepartmentID.
            PopulateDepartmentsDropDownList(_context,Course.DepartmentID);
            return Page();
        }

        public async Task<IActionResult> OnPostAsync(int? id)
        {
            if (!ModelState.IsValid)
            {
                return Page();
            }

            var courseToUpdate = await _context.Courses.FindAsync(id);

            if (await TryUpdateModelAsync<Course>(
                 courseToUpdate,
                 "course",   // Prefix for form value.
                   c => c.Credits, c => c.DepartmentID, c => c.Title))
            {
                await _context.SaveChangesAsync();
                return RedirectToPage("./Index");
            }

            // Select DepartmentID if TryUpdateModelAsync fails.
            PopulateDepartmentsDropDownList(_context, courseToUpdate.DepartmentID);
            return Page();
        }       
    }
}

这些更改与在“创建”页模型中所做的更改相似。 在上面的代码中,PopulateDepartmentsDropDownList在系 ID 中传递并将选择下拉列表中指定的系。

使用以下标记更新 Pages/Courses/Edit.cshtml:

CSHTML

@page
@model ContosoUniversity.Pages.Courses.EditModel

@{
    ViewData["Title"] = "Edit";
}

<h2>Edit</h2>

<h4>Course</h4>
<hr />
<div class="row">
    <div class="col-md-4">
        <form method="post">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <input type="hidden" asp-for="Course.CourseID" />
            <div class="form-group">
                <label asp-for="Course.CourseID" class="control-label"></label>
                <div>@Html.DisplayFor(model => model.Course.CourseID)</div>
            </div>
            <div class="form-group">
                <label asp-for="Course.Title" class="control-label"></label>
                <input asp-for="Course.Title" class="form-control" />
                <span asp-validation-for="Course.Title" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Course.Credits" class="control-label"></label>
                <input asp-for="Course.Credits" class="form-control" />
                <span asp-validation-for="Course.Credits" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Course.Department" class="control-label"></label>
                <select asp-for="Course.DepartmentID" class="form-control" 
                        asp-items="@Model.DepartmentNameSL"></select>
                <span asp-validation-for="Course.DepartmentID" class="text-danger"></span>
            </div>
            <div class="form-group">
                <input type="submit" value="Save" class="btn btn-default" />
            </div>
        </form>
    </div>
</div>

<div>
    <a asp-page="./Index">Back to List</a>
</div>

@section Scripts {
    @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
}

上述标记进行以下更改:

  • 显示课程 ID。 通常不显示实体的主键 (PK)。 PK 对用户不具有任何意义。 在这种情况下,PK 就是课程编号。
  • 将标题从“DepartmentID”更改为“Department”。
  • 将 "ViewBag.DepartmentID" 替换为 DepartmentNameSL(来自基类)。

该页面包含课程编号的隐藏域 (<input type="hidden">)。 添加具有 asp-for="Course.CourseID" 的 <label> 标记帮助器也同样需要隐藏域。 用户单击“保存”时,需要 <input type="hidden">,以便在已发布的数据中包括课程编号。

测试更新的代码。 创建、编辑和删除课程。

将 AsNoTracking 添加到“详细信息”和“删除”页模型

AsNoTracking 可以在不需要跟踪时提高性能。 将 AsNoTracking 添加到“删除”和“详细信息”页模型。下面的代码显示更新的“删除”页模型:

C#

public class DeleteModel : PageModel
{
    private readonly ContosoUniversity.Data.SchoolContext _context;

    public DeleteModel(ContosoUniversity.Data.SchoolContext context)
    {
        _context = context;
    }

    [BindProperty]
    public Course Course { get; set; }

    public async Task<IActionResult> OnGetAsync(int? id)
    {
        if (id == null)
        {
            return NotFound();
        }

        Course = await _context.Courses
            .AsNoTracking()
            .Include(c => c.Department)
            .FirstOrDefaultAsync(m => m.CourseID == id);

        if (Course == null)
        {
            return NotFound();
        }
        return Page();
    }

    public async Task<IActionResult> OnPostAsync(int? id)
    {
        if (id == null)
        {
            return NotFound();
        }

        Course = await _context.Courses
            .AsNoTracking()
            .FirstOrDefaultAsync(m => m.CourseID == id);

        if (Course != null)
        {
            _context.Courses.Remove(Course);
            await _context.SaveChangesAsync();
        }

        return RedirectToPage("./Index");
    }
}

在 Pages/Courses/Details.cshtml.cs 文件中更新 OnGetAsync 方法:

C#

public async Task<IActionResult> OnGetAsync(int? id)
{
    if (id == null)
    {
        return NotFound();
    }

    Course = await _context.Courses
         .AsNoTracking()
         .Include(c => c.Department)
         .FirstOrDefaultAsync(m => m.CourseID == id);

    if (Course == null)
    {
        return NotFound();
    }
    return Page();
}

修改“删除”和“详细信息”页

使用以下标记更新“删除”Razor 页面:

CSHTML

@page
@model ContosoUniversity.Pages.Courses.DeleteModel

@{
    ViewData["Title"] = "Delete";
}

<h2>Delete</h2>

<h3>Are you sure you want to delete this?</h3>
<div>
    <h4>Course</h4>
    <hr />
    <dl class="dl-horizontal">
        <dt>
            @Html.DisplayNameFor(model => model.Course.CourseID)
        </dt>
        <dd>
            @Html.DisplayFor(model => model.Course.CourseID)
        </dd>
        <dt>
            @Html.DisplayNameFor(model => model.Course.Title)
        </dt>
        <dd>
            @Html.DisplayFor(model => model.Course.Title)
        </dd>
        <dt>
            @Html.DisplayNameFor(model => model.Course.Credits)
        </dt>
        <dd>
            @Html.DisplayFor(model => model.Course.Credits)
        </dd>
        <dt>
            @Html.DisplayNameFor(model => model.Course.Department)
        </dt>
        <dd>
            @Html.DisplayFor(model => model.Course.Department.DepartmentID)
        </dd>
    </dl>
    
    <form method="post">
        <input type="hidden" asp-for="Course.CourseID" />
        <input type="submit" value="Delete" class="btn btn-default" /> |
        <a asp-page="./Index">Back to List</a>
    </form>
</div>

对“详细信息”页执行相同更改。

测试“课程”页

测试“创建”、“编辑”、“详细信息”和“删除”。

更新“讲师”页

以下各部分介绍更新“讲师”页。

添加办公室位置

编辑讲师记录时,可能希望更新讲师的办公室分配。 Instructor 实体与 OfficeAssignment 实体是一对零或一关系。 讲师代码必须处理:

  • 如果用户清除办公室分配,则需删除 OfficeAssignment 实体。
  • 如果用户输入办公室分配,且办公室分配原本为空,则需创建一个新 OfficeAssignment 实体。
  • 如果用户更改办公室分配,则需更新 OfficeAssignment 实体。

使用以下代码更新讲师“编辑”页模型:

C#

public class EditModel : PageModel
{
    private readonly ContosoUniversity.Data.SchoolContext _context;

    public EditModel(ContosoUniversity.Data.SchoolContext context)
    {
        _context = context;
    }

    [BindProperty]
    public Instructor Instructor { get; set; }

    public async Task<IActionResult> OnGetAsync(int? id)
    {
        if (id == null)
        {
            return NotFound();
        }

        Instructor = await _context.Instructors
            .Include(i => i.OfficeAssignment)
            .AsNoTracking()
            .FirstOrDefaultAsync(m => m.ID == id);

        if (Instructor == null)
        {
            return NotFound();
        }
        return Page();
    }

    public async Task<IActionResult> OnPostAsync(int? id)
    {
        if (!ModelState.IsValid)
        {
            return Page();
        }

        var instructorToUpdate = await _context.Instructors
            .Include(i => i.OfficeAssignment)
            .FirstOrDefaultAsync(s => s.ID == id);

        if (await TryUpdateModelAsync<Instructor>(
            instructorToUpdate,
            "Instructor",
            i => i.FirstMidName, i => i.LastName, 
            i => i.HireDate, i => i.OfficeAssignment))
        {
            if (String.IsNullOrWhiteSpace(
                instructorToUpdate.OfficeAssignment?.Location))
            {
                instructorToUpdate.OfficeAssignment = null;
            }
            await _context.SaveChangesAsync();
        }
        return RedirectToPage("./Index");

    }
}

前面的代码:

  • 使用 OfficeAssignment 导航属性的预先加载从数据库获取当前的 Instructor 实体。
  • 用模型绑定器中的值更新检索到的 Instructor 实体。 TryUpdateModel 可防止过多发布
  • 如果办公室位置为空,则将 Instructor.OfficeAssignment 设置为 null。 当 Instructor.OfficeAssignment 为 null 时,OfficeAssignment 表中的相关行将会删除。

更新讲师“编辑”页

使用办公室位置更新 Pages/Instructors/Edit.cshtml:

CSHTML

@page
@model ContosoUniversity.Pages.Instructors.EditModel
@{
    ViewData["Title"] = "Edit";
}
<h2>Edit</h2>
<h4>Instructor</h4>
<hr />
<div class="row">
    <div class="col-md-4">
        <form method="post">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <input type="hidden" asp-for="Instructor.ID" />
            <div class="form-group">
                <label asp-for="Instructor.LastName" class="control-label"></label>
                <input asp-for="Instructor.LastName" class="form-control" />
                <span asp-validation-for="Instructor.LastName" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.FirstMidName" class="control-label"></label>
                <input asp-for="Instructor.FirstMidName" class="form-control" />
                <span asp-validation-for="Instructor.FirstMidName" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.HireDate" class="control-label"></label>
                <input asp-for="Instructor.HireDate" class="form-control" />
                <span asp-validation-for="Instructor.HireDate" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.OfficeAssignment.Location" class="control-label"></label>
                <input asp-for="Instructor.OfficeAssignment.Location" class="form-control" />
                <span asp-validation-for="Instructor.OfficeAssignment.Location" class="text-danger" />
            </div>
            <div class="form-group">
                <input type="submit" value="Save" class="btn btn-default" />
            </div>
        </form>
    </div>
</div>

<div>
    <a asp-page="./Index">Back to List</a>
</div>

@section Scripts {
    @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
}

验证是否可以更改讲师办公室位置。

向“讲师编辑”页添加课程分配

讲师可能教授任意数量的课程。 本部分将添加更改课程分配的功能。 下图显示更新的讲师“编辑”页:

带课程信息的讲师“编辑”页

Course 和 Instructor 具有多对多关系。 若要添加和删除关系,可以从 CourseAssignments 联接实体集中添加和删除实体。

通过复选框可对分配给讲师的课程进行更改。 数据库中的每一门课程均有对应显示的复选框。 已分配给讲师的课程将会被勾选。 用户可以通过选择或清除复选框来更改课程分配。 如果课程数量过多:

  • 可以使用其他用户界面显示课程。
  • 使用联接实体创建或删除关系的方法不会发生更改。

添加类以支持“创建”和“编辑”讲师页

使用以下代码创建 SchoolViewModels/AssignedCourseData.cs:

C#

namespace ContosoUniversity.Models.SchoolViewModels
{
    public class AssignedCourseData
    {
        public int CourseID { get; set; }
        public string Title { get; set; }
        public bool Assigned { get; set; }
    }
}

AssignedCourseData 类包含的数据可用于为讲师已分配的课程创建复选框。

创建 Pages/Instructors/InstructorCoursesPageModel.cshtml.cs 基类:

C#

using ContosoUniversity.Data;
using ContosoUniversity.Models;
using ContosoUniversity.Models.SchoolViewModels;
using Microsoft.AspNetCore.Mvc.RazorPages;
using System.Collections.Generic;
using System.Linq;

namespace ContosoUniversity.Pages.Instructors
{
    public class InstructorCoursesPageModel : PageModel
    {

        public List<AssignedCourseData> AssignedCourseDataList;

        public void PopulateAssignedCourseData(SchoolContext context, 
                                               Instructor instructor)
        {
            var allCourses = context.Courses;
            var instructorCourses = new HashSet<int>(
                instructor.CourseAssignments.Select(c => c.CourseID));
            AssignedCourseDataList = new List<AssignedCourseData>();
            foreach (var course in allCourses)
            {
                AssignedCourseDataList.Add(new AssignedCourseData
                {
                    CourseID = course.CourseID,
                    Title = course.Title,
                    Assigned = instructorCourses.Contains(course.CourseID)
                });
            }
        }

        public void UpdateInstructorCourses(SchoolContext context, 
            string[] selectedCourses, Instructor instructorToUpdate)
        {
            if (selectedCourses == null)
            {
                instructorToUpdate.CourseAssignments = new List<CourseAssignment>();
                return;
            }

            var selectedCoursesHS = new HashSet<string>(selectedCourses);
            var instructorCourses = new HashSet<int>
                (instructorToUpdate.CourseAssignments.Select(c => c.Course.CourseID));
            foreach (var course in context.Courses)
            {
                if (selectedCoursesHS.Contains(course.CourseID.ToString()))
                {
                    if (!instructorCourses.Contains(course.CourseID))
                    {
                        instructorToUpdate.CourseAssignments.Add(
                            new CourseAssignment
                            {
                                InstructorID = instructorToUpdate.ID,
                                CourseID = course.CourseID
                            });
                    }
                }
                else
                {
                    if (instructorCourses.Contains(course.CourseID))
                    {
                        CourseAssignment courseToRemove
                            = instructorToUpdate
                                .CourseAssignments
                                .SingleOrDefault(i => i.CourseID == course.CourseID);
                        context.Remove(courseToRemove);
                    }
                }
            }
        }
    }
}

InstructorCoursesPageModel 是将用于“编辑”和“创建”页模型的基类。 PopulateAssignedCourseData 读取所有 Course 实体以填充 AssignedCourseDataList。 该代码将设置每门课程的 CourseID 和标题,并决定是否为讲师分配该课程。 HashSet 用于创建高效查找。

讲师“编辑”页模型

使用以下代码更新讲师“编辑”页模型:

C#

public class EditModel : InstructorCoursesPageModel
{
    private readonly ContosoUniversity.Data.SchoolContext _context;

    public EditModel(ContosoUniversity.Data.SchoolContext context)
    {
        _context = context;
    }

    [BindProperty]
    public Instructor Instructor { get; set; }

    public async Task<IActionResult> OnGetAsync(int? id)
    {
        if (id == null)
        {
            return NotFound();
        }

        Instructor = await _context.Instructors
            .Include(i => i.OfficeAssignment)
            .Include(i => i.CourseAssignments).ThenInclude(i => i.Course)
            .AsNoTracking()
            .FirstOrDefaultAsync(m => m.ID == id);

        if (Instructor == null)
        {
            return NotFound();
        }
        PopulateAssignedCourseData(_context, Instructor);
        return Page();
    }

    public async Task<IActionResult> OnPostAsync(int? id, string[] selectedCourses)
    {
        if (!ModelState.IsValid)
        {
            return Page();
        }

        var instructorToUpdate = await _context.Instructors
            .Include(i => i.OfficeAssignment)
            .Include(i => i.CourseAssignments)
                .ThenInclude(i => i.Course)
            .FirstOrDefaultAsync(s => s.ID == id);

        if (await TryUpdateModelAsync<Instructor>(
            instructorToUpdate,
            "Instructor",
            i => i.FirstMidName, i => i.LastName,
            i => i.HireDate, i => i.OfficeAssignment))
        {
            if (String.IsNullOrWhiteSpace(
                instructorToUpdate.OfficeAssignment?.Location))
            {
                instructorToUpdate.OfficeAssignment = null;
            }
            UpdateInstructorCourses(_context, selectedCourses, instructorToUpdate);
            await _context.SaveChangesAsync();
            return RedirectToPage("./Index");
        }
        UpdateInstructorCourses(_context, selectedCourses, instructorToUpdate);
        PopulateAssignedCourseData(_context, instructorToUpdate);
        return Page();
    }
}

上面的代码处理办公室分配更改。

更新“讲师”Razor 视图:

CSHTML

@page
@model ContosoUniversity.Pages.Instructors.EditModel
@{
    ViewData["Title"] = "Edit";
}
<h2>Edit</h2>
<h4>Instructor</h4>
<hr />
<div class="row">
    <div class="col-md-4">
        <form method="post">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <input type="hidden" asp-for="Instructor.ID" />
            <div class="form-group">
                <label asp-for="Instructor.LastName" class="control-label"></label>
                <input asp-for="Instructor.LastName" class="form-control" />
                <span asp-validation-for="Instructor.LastName" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.FirstMidName" class="control-label"></label>
                <input asp-for="Instructor.FirstMidName" class="form-control" />
                <span asp-validation-for="Instructor.FirstMidName" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.HireDate" class="control-label"></label>
                <input asp-for="Instructor.HireDate" class="form-control" />
                <span asp-validation-for="Instructor.HireDate" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.OfficeAssignment.Location" class="control-label"></label>
                <input asp-for="Instructor.OfficeAssignment.Location" class="form-control" />
                <span asp-validation-for="Instructor.OfficeAssignment.Location" class="text-danger" />
            </div>
            <div class="form-group">
                <div class="col-md-offset-2 col-md-10">
                    <table>
                        <tr>
                            @{
                                int cnt = 0;

                                foreach (var course in Model.AssignedCourseDataList)
                                {
                                    if (cnt++ % 3 == 0)
                                    {
                                        @:</tr><tr>
                                    }
                                    @:<td>
                                        <input type="checkbox"
                                               name="selectedCourses"
                                               value="@course.CourseID"
                                               @(Html.Raw(course.Assigned ? "checked=\"checked\"" : "")) />
                                               @course.CourseID @:  @course.Title
                                    @:</td>
                                }
                                @:</tr>
                            }
                    </table>
                </div>
            </div>
            <div class="form-group">
                <input type="submit" value="Save" class="btn btn-default" />
            </div>
        </form>
    </div>
</div>

<div>
    <a asp-page="./Index">Back to List</a>
</div>

@section Scripts {
    @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
}

 备注

将代码粘贴到 Visual Studio 中时,换行符会发生更改并导致代码中断。 按 Ctrl+Z 一次可撤消自动格式设置。 按 Ctrl+Z 可以修复换行符,使其看起来如此处所示。 缩进不一定要完美,但 @</tr><tr>、@:<td>、@:</td> 和 @:</tr> 行必须各成一行(如下所示)。 选中新的代码块后,按 Tab 三次,使新代码与现有代码对齐。 通过此链接投票或查看此 bug 的状态。

上面的代码将创建一个具有三列的 HTML 表。 每列均具有一个复选框和包含课程编号及标题的标题。 所有复选框均具有相同的名称(“selectedCourses”)。 使用相同名称可指示模型绑定器将它们视为一个组。 每个复选框的值特性都设置为 CourseID。 发布页面时,模型绑定器会传递一个数组,该数组只包括所选复选框的 CourseID 值。

初次呈现复选框时,分配给讲师的课程具有已勾选的特性。

运行应用并测试更新的讲师“编辑”页。 更改某些课程分配。 这些更改将反映在“索引”页上。

注意:此处所使用的编辑讲师课程数据的方法适用于数量有限的课程。 对于规模远大于此的集合,则使用不同的 UI 和不同的更新方法会更实用和更高效。

更新讲师“创建”页

使用以下代码更新讲师“创建”页模型:

C#

using ContosoUniversity.Models;
using Microsoft.AspNetCore.Mvc;
using System.Collections.Generic;
using System.Threading.Tasks;

namespace ContosoUniversity.Pages.Instructors
{
    public class CreateModel : InstructorCoursesPageModel
    {
        private readonly ContosoUniversity.Data.SchoolContext _context;

        public CreateModel(ContosoUniversity.Data.SchoolContext context)
        {
            _context = context;
        }

        public IActionResult OnGet()
        {
            var instructor = new Instructor();
            instructor.CourseAssignments = new List<CourseAssignment>();

            // Provides an empty collection for the foreach loop
            // foreach (var course in Model.AssignedCourseDataList)
            // in the Create Razor page.
            PopulateAssignedCourseData(_context, instructor);
            return Page();
        }

        [BindProperty]
        public Instructor Instructor { get; set; }

        public async Task<IActionResult> OnPostAsync(string[] selectedCourses)
        {
            if (!ModelState.IsValid)
            {
                return Page();
            }

            var newInstructor = new Instructor();
            if (selectedCourses != null)
            {
                newInstructor.CourseAssignments = new List<CourseAssignment>();
                foreach (var course in selectedCourses)
                {
                    var courseToAdd = new CourseAssignment
                    {
                        CourseID = int.Parse(course)
                    };
                    newInstructor.CourseAssignments.Add(courseToAdd);
                }
            }

            if (await TryUpdateModelAsync<Instructor>(
                newInstructor,
                "Instructor",
                i => i.FirstMidName, i => i.LastName,
                i => i.HireDate, i => i.OfficeAssignment))
            {
                _context.Instructors.Add(newInstructor);                
                await _context.SaveChangesAsync();
                return RedirectToPage("./Index");
            }
            PopulateAssignedCourseData(_context, newInstructor);
            return Page();
        }
    }
}

前面的代码与 Pages/Instructors/Edit.cshtml.cs 代码类似。

使用以下标记更新讲师“创建”Razor 页面:

CSHTML

@page
@model ContosoUniversity.Pages.Instructors.CreateModel

@{
    ViewData["Title"] = "Create";
}

<h2>Create</h2>

<h4>Instructor</h4>
<hr />
<div class="row">
    <div class="col-md-4">
        <form method="post">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <div class="form-group">
                <label asp-for="Instructor.LastName" class="control-label"></label>
                <input asp-for="Instructor.LastName" class="form-control" />
                <span asp-validation-for="Instructor.LastName" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.FirstMidName" class="control-label"></label>
                <input asp-for="Instructor.FirstMidName" class="form-control" />
                <span asp-validation-for="Instructor.FirstMidName" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Instructor.HireDate" class="control-label"></label>
                <input asp-for="Instructor.HireDate" class="form-control" />
                <span asp-validation-for="Instructor.HireDate" class="text-danger"></span>
            </div>
            
            <div class="form-group">
                <label asp-for="Instructor.OfficeAssignment.Location" class="control-label"></label>
                <input asp-for="Instructor.OfficeAssignment.Location" class="form-control" />
                <span asp-validation-for="Instructor.OfficeAssignment.Location" class="text-danger" />
            </div>
            <div class="form-group">
                <div class="col-md-offset-2 col-md-10">
                    <table>
                        <tr>
                            @{
                                int cnt = 0;

                                foreach (var course in Model.AssignedCourseDataList)
                                {
                                    if (cnt++ % 3 == 0)
                                    {
                                        @:</tr><tr>
                                    }
                                    @:<td>
                                        <input type="checkbox"
                                               name="selectedCourses"
                                               value="@course.CourseID"
                                               @(Html.Raw(course.Assigned ? "checked=\"checked\"" : "")) />
                                               @course.CourseID @:  @course.Title
                                    @:</td>
                                }
                                @:</tr>
                            }
                    </table>
                </div>
            </div>
            <div class="form-group">
                <input type="submit" value="Create" class="btn btn-default" />
            </div>
        </form>
    </div>
</div>

<div>
    <a asp-page="Index">Back to List</a>
</div>

@section Scripts {
    @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
}

测试讲师“创建”页。

更新“删除”页

使用以下代码更新“删除”页模型:

C#

using ContosoUniversity.Models;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.EntityFrameworkCore;
using System.Linq;
using System.Threading.Tasks;

namespace ContosoUniversity.Pages.Instructors
{
    public class DeleteModel : PageModel
    {
        private readonly ContosoUniversity.Data.SchoolContext _context;

        public DeleteModel(ContosoUniversity.Data.SchoolContext context)
        {
            _context = context;
        }

        [BindProperty]
        public Instructor Instructor { get; set; }

        public async Task<IActionResult> OnGetAsync(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            Instructor = await _context.Instructors.SingleAsync(m => m.ID == id);

            if (Instructor == null)
            {
                return NotFound();
            }
            return Page();
        }

        public async Task<IActionResult> OnPostAsync(int id)
        {
            Instructor instructor = await _context.Instructors
                .Include(i => i.CourseAssignments)
                .SingleAsync(i => i.ID == id);

            var departments = await _context.Departments
                .Where(d => d.InstructorID == id)
                .ToListAsync();
            departments.ForEach(d => d.InstructorID = null);

            _context.Instructors.Remove(instructor);

            await _context.SaveChangesAsync();
            return RedirectToPage("./Index");
        }
    }
}

上面的代码执行以下更改:

  • 对 CourseAssignments 导航属性使用预先加载。 必须包含 CourseAssignments,否则删除讲师时将不会删除课程。 为避免阅读它们,可以在数据库中配置级联删除。
  • 如果要删除的讲师被指派为任何系的管理员,则需从这些系中删除该讲师分配。


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