演练5-1：Contoso大学校园管理1
**演练目的：掌握复杂模型的应用程序开发。
Contoso大学校园管理系统功能包括学生、课程、教师的管理。
一、创建MVC Web应用程序
显示效果如下图，操作步骤略。
二、创建数据模型
1.创建学生实体
using System; using System.Collections.Generic; namespace ContosoUniversity.Models { public class Student { public int StudentID { get; set; } public string LastName { get; set; } public string FirstMidName { get; set; } public DateTime EnrollmentDate { get; set; } public virtual ICollection<Enrollment> Enrollments { get; set; } } }
StudentID属性时主键，EF默认将Id或者classnameID作为主键。
Enrollments属性是导航属性，导航属性拥有与这个实体相关联的实体。此处为学生实体拥有相关的所有课程注册实体，如在数据库中，课程注册表中张三有三条记录，那么导航属性就会有3条Enrollment行。创建导航属性后，数据库数据表将自动生成外键。如果导航属性能包含多个实体（如一对多，多对多），类型必须为集合，比如Icollection。
导航属性通常定义成virtual，这样就可以好好利用EF的lazy loading（延迟加载）功能。延迟加载是指暂时不需要该数据，不用在当前马上加载，而可以推迟到使用它时再加载。延迟加载是一种很重要的数据访问特性，可以有效地减少与数据源的交互（注意，这里所提的交互不是指交互次数，而是指交互的数据量），从而提升程序性能。
2.创建课程实体
using System.Collections.Generic; using System.ComponentModel.DataAnnotations.Schema; namespace ContosoUniversity.Models { public class Course { [DatabaseGenerated(DatabaseGeneratedOption.None)] public int CourseID { get; set; } public string Title { get; set; } public int Credits { get; set; } public virtual ICollection<Enrollment> Enrollments { get; set; } } }
Enrollments属性是导航属性。
CourseID考虑到可能有特殊的数据规则，使用[DatabaseGenerated(DatabaseGeneratedOption.None)]，将不采用数据库自动生成的序号。
3.创建注册实体
namespace ContosoUniversity.Models { public enum Grade { A, B, C, D, F } public class Enrollment { public int EnrollmentID { get; set; } public int CourseID { get; set; } public int StudentID { get; set; } public Grade? Grade { get; set; } public virtual Course Course { get; set; } public virtual Student Student { get; set; } } }
Grade属性是一个enum枚举类型，?表示该属性可以为空。
StudentID属性是一个外键，相应的导航属性是Student。一个注册实体和一个学生实体相关联，所以导航属性拥有一个Student实体，而不是之前的ICollection集合。
CourseID同理。
4.创建数据库上下文
创建一个DAL（Data Access Layer）文件夹，在文件夹中新建SchoolContext.cs类。
using ContosoUniversity.Models; using System.Data.Entity; using System.Data.Entity.ModelConfiguration.Conventions; namespace ContosoUniversity.DAL { public class SchoolContext : DbContext { public DbSet<Student> Students { get; set; } public DbSet<Enrollment> Enrollments { get; set; } public DbSet<Course> Courses { get; set; } } }
这段代码为每个实体集合，创建了一个DbSet属性。在EF技术中，一个实体集合对应一张数据库表，一个实体对应表中的一行。
修改Web.config文件。
<add name="SchoolContext" connectionString="Data Source=(LocalDb)\v11.0;Initial Catalog=ContosoUniversity;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|\ContosoUniversity.mdf" providerName="System.Data.SqlClient" />
默认情况下，EF会寻找DbContext类名字的连接字符串名字。在这个连接字符串中，你已经在App_Data文件夹下添加了一个名字为ContosoUniversity.mdf的LocalDB数据库。如果没有指定连接字符串，EF会为你新建一个。
5.开启Code First Migrations
（1）打开Package Manager控制台
（2）输入命令Enable-Migrations -ContextTypeName SchoolContext
Configuration类包含一个Seed方法，可以在数据库创建时插入一些模型数据，作为测试数据。
namespace ContosoUniversity.Migrations { using System; using System.Collections.Generic; using System.Data.Entity.Migrations; using System.Linq; using ContosoUniversity.Models; internal sealed class Configuration : DbMigrationsConfiguration<ContosoUniversity.DAL.SchoolContext> { public Configuration() { AutomaticMigrationsEnabled = false; } protected override void Seed(ContosoUniversity.DAL.SchoolContext context) { var students = new List<Student> { new Student { FirstMidName = "Carson", LastName = "Alexander", EnrollmentDate = DateTime.Parse("2010-09-01") }, new Student { FirstMidName = "Meredith", LastName = "Alonso", EnrollmentDate = DateTime.Parse("2012-09-01") }, new Student { FirstMidName = "Arturo", LastName = "Anand", EnrollmentDate = DateTime.Parse("2013-09-01") }, new Student { FirstMidName = "Gytis", LastName = "Barzdukas", EnrollmentDate = DateTime.Parse("2012-09-01") }, new Student { FirstMidName = "Yan", LastName = "Li", EnrollmentDate = DateTime.Parse("2012-09-01") }, new Student { FirstMidName = "Peggy", LastName = "Justice", EnrollmentDate = DateTime.Parse("2011-09-01") }, new Student { FirstMidName = "Laura", LastName = "Norman", EnrollmentDate = DateTime.Parse("2013-09-01") }, new Student { FirstMidName = "Nino", LastName = "Olivetto", EnrollmentDate = DateTime.Parse("2005-08-11") } }; students.ForEach(s => context.Students.AddOrUpdate(p => p.LastName, s)); context.SaveChanges(); var courses = new List<Course> { new Course {CourseID = 1050, Title = "Chemistry", Credits = 3, }, new Course {CourseID = 4022, Title = "Microeconomics", Credits = 3, }, new Course {CourseID = 4041, Title = "Macroeconomics", Credits = 3, }, new Course {CourseID = 1045, Title = "Calculus", Credits = 4, }, new Course {CourseID = 3141, Title = "Trigonometry", Credits = 4, }, new Course {CourseID = 2021, Title = "Composition", Credits = 3, }, new Course {CourseID = 2042, Title = "Literature", Credits = 4, } }; courses.ForEach(s => context.Courses.AddOrUpdate(p => p.Title, s)); context.SaveChanges(); var enrollments = new List<Enrollment> { new Enrollment { StudentID = students.Single(s => s.LastName == "Alexander").StudentID, CourseID = courses.Single(c => c.Title == "Chemistry" ).CourseID, Grade = Grade.A }, new Enrollment { StudentID = students.Single(s => s.LastName == "Alexander").StudentID, CourseID = courses.Single(c => c.Title == "Microeconomics" ).CourseID, Grade = Grade.C }, new Enrollment { StudentID = students.Single(s => s.LastName == "Alexander").StudentID, CourseID = courses.Single(c => c.Title == "Macroeconomics" ).CourseID, Grade = Grade.B }, new Enrollment { StudentID = students.Single(s => s.LastName == "Alonso").StudentID, CourseID = courses.Single(c => c.Title == "Calculus" ).CourseID, Grade = Grade.B }, new Enrollment { StudentID = students.Single(s => s.LastName == "Alonso").StudentID, CourseID = courses.Single(c => c.Title == "Trigonometry" ).CourseID, Grade = Grade.B }, new Enrollment { StudentID = students.Single(s => s.LastName == "Alonso").StudentID, CourseID = courses.Single(c => c.Title == "Composition" ).CourseID, Grade = Grade.B }, new Enrollment { StudentID = students.Single(s => s.LastName == "Anand").StudentID, CourseID = courses.Single(c => c.Title == "Chemistry" ).CourseID }, new Enrollment { StudentID = students.Single(s => s.LastName == "Anand").StudentID, CourseID = courses.Single(c => c.Title == "Microeconomics").CourseID, Grade = Grade.B }, new Enrollment { StudentID = students.Single(s => s.LastName == "Barzdukas").StudentID, CourseID = courses.Single(c => c.Title == "Chemistry").CourseID, Grade = Grade.B }, new Enrollment { StudentID = students.Single(s => s.LastName == "Li").StudentID, CourseID = courses.Single(c => c.Title == "Composition").CourseID, Grade = Grade.B }, new Enrollment { StudentID = students.Single(s => s.LastName == "Justice").StudentID, CourseID = courses.Single(c => c.Title == "Literature").CourseID, Grade = Grade.B } }; foreach (Enrollment e in enrollments) { var enrollmentInDataBase = context.Enrollments.Where( s => s.Student.StudentID == e.StudentID && s.Course.CourseID == e.CourseID).SingleOrDefault(); if (enrollmentInDataBase == null) { context.Enrollments.Add(e); } } context.SaveChanges(); } } }
Seed方法使用数据库context对象作为输入参数，使用这个对象把新的实体插入到数据库中。每一个实体类型，代码都创建了一个新的实体集合，把它们添加到相应的DbSet属性中，然后保存到数据库中。
AddOrUpdate方法，第一个参数用来检查一个行是否已经存在，第二个参数是插入的值。
Enrollment实体并没有使用AddOrUpdate方法，而是使用循环遍历Enrollment集合，判断是不是已经存在。
（3）add-migration InitialCreate
（4）update-database
运行Up方法创建数据库，并运行Seed方法填充数据库。
三、创建Student控制器和视图
1.创建Student控制器，选择自动生成控制器代码和视图。
**Conventions
- 实体类名字的复数，被用作数据库表名
- 实体属性的名字，被用作列名
- Id或ClassnameID属性，被标识为主键。
2.创建Details页面
在EnrollmentDate后面，<fieldset>之前，添加显示注册信息列表的代码。
<div class="display-label"> @Html.LabelFor(model => model.Enrollments) </div> <div class="display-field"> <table> <tr> <th>Course Title</th> <th>Grade</th> </tr> @foreach (var item in Model.Enrollments) { <tr> <td> @Html.DisplayFor(modelItem => item.Course.Title) </td> <td> @Html.DisplayFor(modelItem => item.Grade) </td> </tr> } </table> </div> </fieldset> <p> @Html.ActionLink("Edit", "Edit", new { id=Model.StudentID }) | @Html.ActionLink("Back to List", "Index") </p>
3.更新Create页面
更新HttpPost Create方法，添加try-catch和Bind attribute
[HttpPost] [ValidateAntiForgeryToken] public ActionResult Create( [Bind(Include = "LastName, FirstMidName, EnrollmentDate")] Student student) { try { if (ModelState.IsValid) { db.Students.Add(student); 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."); } return View(student); }
这段代码使用模型绑定添加Student实体，并保存至数据库。
ValidateAntiForgeryToken属性，帮助伪造响应跨站攻击。需要在Create视图中，表单里面添加语句“@Html.AntiForgeryToken()”。
Bind属性用来保护过度提交。例如，假设Student实体包含一个Secret属性，你不想通过网页更新。Exclude参数阻止你希望排除的黑名单字段。
public class Student { public int StudentID { get; set; } public string LastName { get; set; } public string FirstMidName { get; set; } public DateTime EnrollmentDate { get; set; } public string Secret { get; set; } public virtual ICollection<Enrollment> Enrollments { get; set; } }
4.更新HttpPost Edit方法
[HttpPost] [ValidateAntiForgeryToken] public ActionResult Edit( [Bind(Include = "StudentID, LastName, FirstMidName, EnrollmentDate")] Student student) { try { if (ModelState.IsValid) { db.Entry(student).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."); } return View(student); }
Entity状态有Added、Unchanged、Modified、Delete、Detached。
5.更新Delete页面
public ActionResult Delete(bool? saveChangesError=false, int id = 0) { if (saveChangesError.GetValueOrDefault()) { ViewBag.ErrorMessage = "Delete failed. Try again, and if the problem persists see your system administrator."; } Student student = db.Students.Find(id); if (student == null) { return HttpNotFound(); } return View(student); }
[HttpPost] [ValidateAntiForgeryToken] public ActionResult Delete(int id) { try { Student student = db.Students.Find(id); db.Students.Remove(student); db.SaveChanges(); } catch (DataException/* dex */) { // uncomment dex and log error. return RedirectToAction("Delete", new { id = id, saveChangesError = true }); } return RedirectToAction("Index"); }
在Views\Student\Delete.cshtml页面中，添加错误消息。
<h2>Delete</h2> <p class="error">@ViewBag.ErrorMessage</p> <h3>Are you sure you want to delete this?</h3>
