Question

好的，我是MVC的新手，我只是尝试了一个简单的例子，我从数据库中获取数据并在简单的网页中显示它。

我正在做这个教程。

我创建了3个名为Student，Course，Enrollment的文章。

他们是：

public class Student
    {
        public int StudentId {get; set;}
        public string LastName { get; set; }
        public string FirstName { get; set; }
   //     public DateTime EnrollmentDate { get; set; }
        public List<Enrollment> Enrollments { get; set; }
    }

public class Course
    {
        public int CourseId { get; set; }
        public string CourseName {get; set;}
        public int TotalCredits { get; set; }
        public List<Enrollment> Enrollments { get; set; }
    }


public class Enrollment
    {
        public int EnrollmentID { get; set; }
        public int CourseId { get; set; }
        public int StudentId { get; set; }
        public decimal? Grade { get; set; }
        public Student Student { get; set; }
        public Course Course { get; set; }
    }

请注意，学生有一个入学列表，与课程相同。那个Enrollments有一个Sudent实例和一个Course实例。这告诉数据库如何将不同的表相互连接。

我在XyzController中创建了一个简单的Action方法，它从数据库中提取数据，将其传递给View并将View（）的返回转发给浏览器：

XyzController.cs

public class XyzController : Controller
    {
        private SchoolContext db = new SchoolContext();

        public ActionResult Abc()
        {

            var students = db.Students.ToList();
            var courses = db.Courses.ToList();
            var enrollments = db.Enrollments.ToList();

            Courses_Students_Enrollments obj = new Courses_Students_Enrollments();
            obj.courses = courses;
            obj.students = students;
            obj.enrollments = enrollments;

            return View(obj);

        }

这是View（Abc.cshtml文件），它使用Controller中Action方法传递的数据创建View：

Abc.cshtml

    @model WebApplication.ViewModels.Courses_Students_Enrollments
    @{
        ViewBag.Title = "Abc Page";
    }

    <h2>This is Abc.cshtml under the folder View/Xyz</h2>

     @* <h2>Course Tittle: @Model.course.CourseName</h2> *@

    <br />
    Students:
    @foreach (var item in Model.students) {
    <h2>Student Name: @item.FirstName @item.LastName</h2>
    }
    <br />

    Courses:
    @foreach (var item in Model.courses) {
    <h2>Course Tittle: @item.CourseName @item.TotalCredits</h2>
    }
    <br />

    Enrollments:
    @foreach (var item in Model.enrollments) {
    <h2>Enrollments: @item.CourseId @item.StudentId</h2>
    }

现在进入数据库。

这是Class SchoolContext，它扩展了DbContext，并且像数据库接口一样运行（种类）。我在类中放入了我想要的每个类的DbSet。

SchoolContext.cs

public class SchoolContext : DbContext
    {   //This class enables CRUD (Create, Read, Update, Delete) functionality 
        public DbSet<Student> Students { get; set; }
        public DbSet<Course> Courses { get; set; }
        public DbSet<Enrollment> Enrollments { get; set; }
    }

在从数据库中获取数据之前，有必要引入一些数据。

此类将使用每个表的一些记录初始化数据库。

SchoolInitializer.cs

    public class SchoolInitializer : DropCreateDatabaseIfModelChanges<SchoolContext>
        {
            protected override void Seed(SchoolContext context)
            {
                var students = new List<Student> 
                {
                    new Student{FirstName = "James", LastName = "Dean")},
                    new Student{FirstName = "Lynda", LastName = "Thames")}
                };
                foreach (var temp in students)
                {
                    context.Students.Add(temp);
                }

                var courses = new List<Course> 
                {
                    new Course{CourseName = "Java", TotalCredits = 4},
                    new Course{CourseName = "C#", TotalCredits = 4}
                };
                foreach (var temp in courses)
                {
                    context.Courses.Add(temp);
                }

                var enrollments = new List<Enrollment> 
                {
                    new Enrollment{StudentId = 1, CourseId = 1, Grade = 3},
                    new Enrollment{StudentId = 1, CourseId = 2, Grade = 4}
                };
                foreach (var temp in enrollments)
                {
                    context.Enrollments.Add(temp);
                }

        -->     context.SaveChanges();
            }
}

这里在Application_start（）

上调用了SchoolInitializer类

Global.asax中

namespace WebApplication
    {
        public class MvcApplication : System.Web.HttpApplication
        {
            protected void Application_Start()
            {
        -->     Database.SetInitializer<SchoolContext>(new SchoolInitializer());
                AreaRegistration.RegisterAllAreas();
                FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
                RouteConfig.RegisterRoutes(RouteTable.Routes);
                BundleConfig.RegisterBundles(BundleTable.Bundles);
            }
        }
    }

一切正常，数据库中的数据已由控制器提取，传递给View并显示在浏览器中。但是，在再次运行项目后，修改SchoolInitializer中的记录不会影响数据库，数据库保持不变，并在第一次初始化时使用第一个数据。

{我解决了我写这个问题的问题:)所以，谢谢大家;）}

解决方案：当数据库不存在时，Global.asax中的Application_Start（）仅调用SchoolInitializer。一旦创建，ApplicationInstializer将不会被Application_start（）调用。

离开这篇文章以防有人可以受益：）

数据库未初始化/播种

0 个答案: