演练5-5:Contoso大学校园管理系统5

      Contoso University示例网站演示如何使用Entity Framework 5创建ASP.NET MVC 4应用程序。 Entity Framework有三种处理数据的方式:  Database First ,  Model First , and  Code First . 本指南使用代码优先。其它方式请查询资料。 示例程序是为Contoso University建立一个网站。功能包括:学生管理、课程创建、教师分配。 本系列指南逐步讲述如何实现这一网站程序。

      如有问题,可在这些讨论区提问:  ASP.NET Entity Framework forum , the  Entity Framework and LINQ to Entities forum , or  StackOverflow.com .

上一节完成了相关联数据的显示,本节将学习如何更新关联数据。大部分关联关系可通过更新相应的外键来完成。对于多对多关系,EF没有直接暴漏连接表,需要显式的操作导航属性(向其中添加、移除实体)来完成。

一、定制课程的Create和Edit页面

      将要完成的效果如下:

      课程实体创建后是和某个部门有关联的。为了展示这一点,自动生成的代码生成了相应的控制器方法以及创建、编辑视图,其中包括可选择部门的下拉列表。下拉列表设置   Course.DepartmentID 外键属性,这样 EF 就可以正确加载 Department   导航属性的对应实体。这里只简单修改代码,增加错误处理和下拉列表排序功能。 
1.在CourseController.cs中修改Edit和Create动作代码

public ActionResult Create()
{
   PopulateDepartmentsDropDownList();
   return View();
}

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create(
   [Bind(Include = "CourseID,Title,Credits,DepartmentID")]
   Course course)
{
   try
   {
      if (ModelState.IsValid)
      {
         db.Courses.Add(course);
         db.SaveChanges();
         return RedirectToAction("Index");
      }
   }
   catch (DataException /* dex */)
   {
      //Log the error (uncomment dex variable name after DataException and add a line here to write a log.)
      ModelState.AddModelError("", "Unable to save changes. Try again, and if the problem persists, see your system administrator.");
   }
   PopulateDepartmentsDropDownList(course.DepartmentID);
return View(course);
}

public ActionResult Edit(int id)
{
   Course course = db.Courses.Find(id);
   PopulateDepartmentsDropDownList(course.DepartmentID);
return View(course);
}

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Edit(
    [Bind(Include = "CourseID,Title,Credits,DepartmentID")]
    Course course)
{
   try
   {
      if (ModelState.IsValid)
      {
         db.Entry(course).State = EntityState.Modified;
         db.SaveChanges();
         return RedirectToAction("Index");
      }
   }
   catch (DataException /* dex */)
   {
      //Log the error (uncomment dex variable name after DataException and add a line here to write a log.)
      ModelState.AddModelError("", "Unable to save changes. Try again, and if the problem persists, see your system administrator.");
   }
   PopulateDepartmentsDropDownList(course.DepartmentID);
   return View(course);
}

private void PopulateDepartmentsDropDownList(object selectedDepartment = null)
{
   var departmentsQuery = from d in db.Departments
                          orderby d.Name
                          select d;
   ViewBag.DepartmentID = new SelectList(departmentsQuery, "DepartmentID", "Name", selectedDepartment);
} 

      PopulateDepartmentsDropDownList方法获取按名排列的部门列表,为下拉列表构建一个SelectList集合,使用ViewBag属性将其传递到视图。该方法有一个可选参数     selectedDepartment,以便设置下拉列表默认值。相关视图将把DepartmentID传递给DropDownList帮助器, 帮助器从ViewBag中寻找名为DepartmentIDSelectList。  

      HttpGet Create调用PopulateDepartmentsDropDownList方法时不使用默认值,因为此时还没有创建新课程数据:

public ActionResult Create()
{
    PopulateDepartmentsDropDownList();
    return View();
}

     HttpGet Edit方法则设置默认值,因为此时课程在编辑时有原始的部门信息:

public ActionResult Edit(int id)
{
    Course course = db.Courses.Find(id);
    PopulateDepartmentsDropDownList(course.DepartmentID);
    return View(course);
}

     HttpPost方法在捕获异常之后再次显示创建或编辑页面时,初始化下拉列表默认值:

catch (DataException /* dex */)
   {
      //Log the error (uncomment dex variable name after DataException and add a line here to write a log.)
      ModelState.AddModelError("", "Unable to save changes. Try again, and if the problem persists, see your system administrator.");
   }
   PopulateDepartmentsDropDownList(course.DepartmentID);
   return View(course);

       代码确保如果发生异常返回页面时,原有的操作数据还在。

 2.修改Create视图

      在Views\Course\Create.cshtml, 在Title域之前添加代码,提供录入课程编号的编辑域。之前曾经介绍过,自动生成代码不会保护对主键的编辑域。

model ContosoUniversity.Models.Course

@{
    ViewBag.Title = "Create";
}

<h2>Create</h2>

@using (Html.BeginForm())
{
    @Html.AntiForgeryToken()
    @Html.ValidationSummary(true)

    <fieldset>
        <legend>Course</legend>

        <div class="editor-label">
            @Html.LabelFor(model => model.CourseID)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.CourseID)
            @Html.ValidationMessageFor(model => model.CourseID)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.Title)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.Title)
            @Html.ValidationMessageFor(model => model.Title)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.Credits)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.Credits)
            @Html.ValidationMessageFor(model => model.Credits)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.DepartmentID, "Department")
        </div>
        <div class="editor-field">
            @Html.DropDownList("DepartmentID", String.Empty)
            @Html.ValidationMessageFor(model => model.DepartmentID)
        </div>

        <p>
            <input type="submit" value="Create" />
        </p>
    </fieldset>
}

<div>
    @Html.ActionLink("Back to List", "Index")
</div>

@section Scripts {
    @Scripts.Render("~/bundles/jqueryval")
}

      同样地修改Views\Course\Edit、Delete和Details视图,在Title字段前添加course number字段。

<div class="display-label">
         @Html.DisplayNameFor(model => model.CourseID)
    </div>
    <div class="display-field">
         @Html.DisplayFor(model => model.CourseID)
</div>

      运行Create、Edit、Delete、Details,查看效果。

 

二、为教师创建Edit页面

    

      当你编辑一条教师记录时,你可能希望能够更新教师的办公地点。Instructor实体和OfficeAssignment之间是一对一的关系,所以必须处理以下情况:

  • 如果用户清除了办公地点,而它本来是有值的,那么你必须删除OfficeAssignment实体。
  • 如果用户输入办公地点值,而它本来是空的,那么你必须新建一个OfficeAssignment实体。
  • 如果用户改变了办公地点的值,那么你必须改变已有的OfficeAssignment实体值。

1.添加办公地点

      Instructor控制器中,自动生成的HttpGet Edit方法代码如下:

public ActionResult Edit(int id = 0)
{
    Instructor instructor = db.Instructors.Find(id);
    if (instructor == null)
    {
        return HttpNotFound();
    }
    ViewBag.InstructorID = new SelectList(db.OfficeAssignments, "InstructorID", "Location", instructor.InstructorID);
    return View(instructor);
}

      自动生成的代码创建了下拉列表,我们将其修改以下,使用文本框:

public ActionResult Edit(int id)
{
    Instructor instructor = db.Instructors
        .Include(i => i.OfficeAssignment)
        .Where(i => i.InstructorID == id)
        .Single();
    return View(instructor);
}

      使用eager loading贪婪加载方式获取OfficeAssignment实体,就不能使用Find方法,所以我们使用了Where。

      将HttpPost Edit方法替换为如下代码。

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Edit(int id, FormCollection formCollection)
{
   var instructorToUpdate = db.Instructors
       .Include(i => i.OfficeAssignment)
       .Where(i => i.InstructorID == id)
       .Single();

   if (TryUpdateModel(instructorToUpdate, "",
      new string[] { "LastName", "FirstMidName", "HireDate", "OfficeAssignment" }))
   {
      try
      {
         if (String.IsNullOrWhiteSpace(instructorToUpdate.OfficeAssignment.Location))
         {
            instructorToUpdate.OfficeAssignment = null;
         }

         db.Entry(instructorToUpdate).State = EntityState.Modified;
         db.SaveChanges();

         return RedirectToAction("Index");
      }
      catch (DataException /* dex */)
      {
         //Log the error (uncomment dex variable name after DataException and add a line here to write a log.
         ModelState.AddModelError("", "Unable to save changes. Try again, and if the problem persists, see your system administrator.");
      }
   }
   ViewBag.InstructorID = new SelectList(db.OfficeAssignments, "InstructorID", "Location", id);
   return View(instructorToUpdate);
}

      这部分代码的作用是:  

  • 从数据库通过贪婪加载获取InstructorOfficeAssignment实体。这是和自动生成的HttpGet Edit方法一样的。

  • 使用模型绑定器数据更新Instructor实体。

if (TryUpdateModel(instructorToUpdate, "",
      new string[] { "LastName", "FirstMidName", "HireDate", "OfficeAssignment" }))
  • 如果办公室信息为空,将Instructor.OfficeAssignment属性设为null,OfficeAssignment表中相应的记录也将删除。
if (String.IsNullOrWhiteSpace(instructorToUpdate.OfficeAssignment.Location))
{
    instructorToUpdate.OfficeAssignment = null;
}
  • 保存对数据库的修改。

      在Views\Instructor\Edit.cshtmlHire Date div标记之后, 添加办公室信息的编辑域:

<div class="editor-label">
    @Html.LabelFor(model => model.OfficeAssignment.Location)
</div>
<div class="editor-field">
    @Html.EditorFor(model => model.OfficeAssignment.Location)
    @Html.ValidationMessageFor(model => model.OfficeAssignment.Location)
</div>

      运行,测试效果。

 

2.添加教师讲授的课程数据更新

      在教师Edit页面,增加对教师承担课程编辑的功能,效果如下。

      Course和Instructor实体之间是多对过关系,我们并没有手动生成它们之间的连接表,自动生成的连接表无法直接访问。事实上,我们将通过在Instructor.Courses导航属性中,添加或删除关联实体的方式来实现关系的维护。

      改变老师承担课程的功能,是通过一组复选框来实现。列出数据库中所有课程,教师承担某课程,则该复选框选中。用户通过选中或者取消选中的操作修改课程的分配情况。如果课程数目很多,你可能希望使用别的显示方法,但操作导航属性来添加或删除关系的方法是一样的。  

      为了能够显示这一组复选框,我们将使用视图模型类。在Models文件夹中,创建AssignedCourseData.cs文件。

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

      更新Instructor控制器的Edit方法。

public ActionResult Edit(int id)
{
    Instructor instructor = db.Instructors
        .Include(i => i.OfficeAssignment)
        .Include(i => i.Courses)
        .Where(i => i.InstructorID == id)
        .Single();
    PopulateAssignedCourseData(instructor);
    return View(instructor);
}

private void PopulateAssignedCourseData(Instructor instructor)
{
    var allCourses = db.Courses;
    var instructorCourses = new HashSet<int>(instructor.Courses.Select(c => c.CourseID));
    var viewModel = new List<AssignedCourseData>();
    foreach (var course in allCourses)
    {
        viewModel.Add(new AssignedCourseData
        {
            CourseID = course.CourseID,
            Title = course.Title,
            Assigned = instructorCourses.Contains(course.CourseID)
        });
    }
    ViewBag.Courses = viewModel;
}

      代码使用贪婪模式加载Courses导航属性,调用PopulateAssignedCourseData方法实现为视图提供AssignedCourseData视图模型的数据。  

      PopulateAssignedCourseData方法读取所有Course实体。对每一个Courses检查是否已经存在于某教师的导航属性中。为了提高效率,将当前承担课程的ID形成一个HashSet 集合。教师承担某课程,则Assigned属性将设为 true。视图将使用此属性决定哪些选择框处于被选中状态。最后通过ViewBag的一个属性将列表传递到视图。

      下一步,完成保存代码。使用如下代码替换HttpPost Edit方法的代码,调用一个新的方法更新Instructor实体的Courses导航属性。

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Edit(int id, FormCollection formCollection, string[] selectedCourses)
{
   var instructorToUpdate = db.Instructors
       .Include(i => i.OfficeAssignment)
       .Include(i => i.Courses)
       .Where(i => i.InstructorID == id)
       .Single();
   if (TryUpdateModel(instructorToUpdate, "", 
      new string[] { "LastName", "FirstMidName", "HireDate", "OfficeAssignment" }))
   {
      try
      {
         if (String.IsNullOrWhiteSpace(instructorToUpdate.OfficeAssignment.Location))
         {
            instructorToUpdate.OfficeAssignment = null;
         }

         UpdateInstructorCourses(selectedCourses, instructorToUpdate);

         db.Entry(instructorToUpdate).State = EntityState.Modified;
         db.SaveChanges();

         return RedirectToAction("Index");
      }
      catch (DataException /* dex */)
      {
         //Log the error (uncomment dex variable name after DataException and add a line here to write a log.
         ModelState.AddModelError("", "Unable to save changes. Try again, and if the problem persists see your system administrator.");
      }
   }
   PopulateAssignedCourseData(instructorToUpdate);
return View(instructorToUpdate);
}

private void UpdateInstructorCourses(string[] selectedCourses, Instructor instructorToUpdate)
{
   if (selectedCourses == null)
   {
      instructorToUpdate.Courses = new List<Course>();
      return;
   }

   var selectedCoursesHS = new HashSet<string>(selectedCourses);
   var instructorCourses = new HashSet<int>
       (instructorToUpdate.Courses.Select(c => c.CourseID));
   foreach (var course in db.Courses)
   {
      if (selectedCoursesHS.Contains(course.CourseID.ToString()))
      {
         if (!instructorCourses.Contains(course.CourseID))
         {
            instructorToUpdate.Courses.Add(course);
         }
      }
      else
      {
         if (instructorCourses.Contains(course.CourseID))
         {
            instructorToUpdate.Courses.Remove(course);
         }
      }
   }

       因为自动生成的视图中,不包含Course实体集合, 因此模型绑定器不能直接更新Courses导航属性。更新由UpdateInstructorCourses方法完成。因此要把Courses属性从模型绑定器中排除出去。这并不需要修改TryUpdateModel的代码,因为使用了白名单,Courses不在名单之内。

      如果没有选中任何课程,UpdateInstructorCoursesCourses导航属性设为一个空的列表:

if (selectedCourses == null)
{
    instructorToUpdate.Courses = new List<Course>();
    return;
}

      代码执行循环检查数据库中的每一课程,若此课程被选中则判断是否已经包含在相关数据中,如果没有则添加到导航属性。为了提高效率,把选中课程 Id和已有课程ID放在哈希表中。

if (selectedCoursesHS.Contains(course.CourseID.ToString()))
{
    if (!instructorCourses.Contains(course.CourseID))
    {
        instructorToUpdate.Courses.Add(course);
    }
}

      如果某课程没有选中但存在于Instructor.Courses导航属性则将其从中移除。

else
{
    if (instructorCourses.Contains(course.CourseID))
    {
        instructorToUpdate.Courses.Remove(course);
    }
}

      在Views\Instructor\Edit.cshtml文件中,在OfficeAssignment之后,添加课程复选框。

@model ContosoUniversity.Models.Instructor

@{
    ViewBag.Title = "Edit";
}

<h2>Edit</h2>

@using (Html.BeginForm())
{
    @Html.AntiForgeryToken()
    @Html.ValidationSummary(true)

    <fieldset>
        <legend>Instructor</legend>

        @Html.HiddenFor(model => model.InstructorID)
             

        <div class="editor-label">
            @Html.LabelFor(model => model.LastName)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.LastName)
            @Html.ValidationMessageFor(model => model.LastName)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.FirstMidName)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.FirstMidName)
            @Html.ValidationMessageFor(model => model.FirstMidName)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.HireDate)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.HireDate)
            @Html.ValidationMessageFor(model => model.HireDate)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.OfficeAssignment.Location)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.OfficeAssignment.Location)
            @Html.ValidationMessageFor(model => model.OfficeAssignment.Location)
        </div>

        <div class="editor-field">
    <table>
        <tr>
            @{
                int cnt = 0;
                List<ContosoUniversity.ViewModels.AssignedCourseData> courses = ViewBag.Courses;

                foreach (var course in courses) {
                    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>
        <p>
            <input type="submit" value="Save" />
        </p>
    </fieldset>
}

<div>
    @Html.ActionLink("Back to List", "Index")
</div>

@section Scripts {
    @Scripts.Render("~/bundles/jqueryval")
}

      这段代码创建了一个包含三列的表格。每一列包含一个复选框、课程编号和名称。所有复选框的名字都是一样的 ("selectedCourses"), 模型绑定器由此得知将其作为一组信息来处理。复选框的 value设为对于课程的 CourseID。当编辑提交之后,模型绑定器将被选中的复选框的值组合为一个数组传给控制器。

      更新Views\Instructor\Index.cshtml视图,在Office列之后添加Courses,更新Details视图。

@model ContosoUniversity.ViewModels.InstructorIndexData

@{
    ViewBag.Title = "Instructors";
}

<h2>Instructors</h2>

<p>
    @Html.ActionLink("Create New", "Create")
</p>
<table>
    <tr>
        <th></th>
        <th>Last Name</th>
        <th>First Name</th>
        <th>Hire Date</th>
        <th>Office</th>
        <th>Courses</th>
    </tr>
    @foreach (var item in Model.Instructors)
    {
        string selectedRow = "";
        if (item.InstructorID == ViewBag.InstructorID)
        {
            selectedRow = "selectedrow";
        } 
        <tr class="@selectedRow" valign="top">
            <td>
                @Html.ActionLink("Select", "Index", new { id = item.InstructorID }) | 
                @Html.ActionLink("Edit", "Edit", new { id = item.InstructorID }) | 
                @Html.ActionLink("Details", "Details", new { id = item.InstructorID }) | 
                @Html.ActionLink("Delete", "Delete", new { id = item.InstructorID })
            </td>
            <td>
                @item.LastName
            </td>
            <td>
                @item.FirstMidName
            </td>
            <td>
                @String.Format("{0:d}", item.HireDate)
            </td>
            <td>
                @if (item.OfficeAssignment != null)
                { 
                    @item.OfficeAssignment.Location  
                }
            </td>
            <td>
                @{
                foreach (var course in item.Courses)
                {
                    @course.CourseID @:  @course.Title <br />
                }
                }
            </td>
        </tr> 
    }
</table>

@if (Model.Courses != null)
{ 
    <h3>Courses Taught by Selected Instructor</h3> 
    <table>
        <tr>
            <th></th>
            <th>ID</th>
            <th>Title</th>
            <th>Department</th>
        </tr>

        @foreach (var item in Model.Courses)
        {
            string selectedRow = "";
            if (item.CourseID == ViewBag.CourseID)
            {
                selectedRow = "selectedrow";
            } 
        
            <tr class="@selectedRow">

                <td>
                    @Html.ActionLink("Select", "Index", new { courseID = item.CourseID })
                </td>
                <td>
                    @item.CourseID
                </td>
                <td>
                    @item.Title
                </td>
                <td>
                    @item.Department.Name
                </td>
            </tr> 
        }

    </table> 
}
@if (Model.Enrollments != null)
{ 
    <h3>Students Enrolled in Selected Course</h3> 
    <table>
        <tr>
            <th>Name</th>
            <th>Grade</th>
        </tr>
        @foreach (var item in Model.Enrollments)
        { 
            <tr>
                <td>
                    @item.Student.FullName
                </td>
                <td>
                    @Html.DisplayFor(modelItem => item.Grade)
                </td>
            </tr> 
        }
    </table> 
}

       运行Instructor Index,查看效果。点击Edit查看功能,修改一些课程的分配,然后点击Save,修改结果在Index页面展示。

      这种方式在课程数目不多时有效。如果课程数目很多需要修改显示方式和更新方法。

3.更新Instructor的Delete方法

      修改代码,当删除教师时,为其分配的办公室信息随之删除:

 [HttpPost, ActionName("Delete")]
        [ValidateAntiForgeryToken]
        public ActionResult DeleteConfirmed(int id)
        {
            Instructor instructor = db.Instructors
              .Include(i => i.OfficeAssignment)
              .Where(i => i.InstructorID == id)
              .Single();
 
            foreach (var department in db.Departments)
            {
                if (department.InstructorID == id)
                {
                    department.InstructorID = null;
                }
            }
            db.Instructors.Remove(instructor);
            db.SaveChanges();
            return RedirectToAction("Index");
        }

    

      已经完成了完整的CRUD操作,但没有处理同步问题。下一节将引入同步问题,介绍处理方法,为CRUD操作添加同步处理。

视频教程: 12

posted @ 2014-10-23 16:09  liesl  阅读(494)  评论(2编辑  收藏  举报