Question

我是.net web developpment的新手，我正在使用ASP.net开发一个rest API，问题是我希望通过名字让学生把它放在URL中，这是我的模型class Student.cs：

 public partial class Student : BaseEntity
        {

            public string FirstName { get; set; }
            public string LastName { get; set; }

//constructor of the Student
 public Student()
        {
            Attendances = new List<Attendance>();
            StudentComments = new List<StudentComment>();
        }
 }

这是我的dataBase数据初始化代码：SMADBInitializer.cs

var Students = new List<Student>  //I get the error in this line
            {
            new Student{FirstName="sam", LastName="9"},
            }

SMAContext.cs：

public partial class SMAContext : DataContext
    {
        static SMAContext()
        {
            Database.SetInitializer<SMAContext>(new SMADBInitializer());
        }

        public SMAContext()
            : base("Name=SMAContext")
        {
        }        
public DbSet<Student> Students { get; set; }
}

StudentsController.cs：

private static SMAContext cc = new SMAContext();
    [Route("api/Students/{name:alpha}")]
            public string Get(string name)
            {
                var query = from Students in cc.Students
                            where Students.FirstName.Contains(name)
                            select Students.FirstName;

                var students = query.ToList();
                HttpResponseMessage response = Request.CreateResponse(HttpStatusCode.OK, students);
                return response.ToString();
            }

这是RouteConfig类：

public class RouteConfig
    {
        public static void RegisterRoutes(RouteCollection routes)
        {
            routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

            routes.MapRoute(
                name: "Default",
                url: "{controller}/{action}/{id}",
                defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
            );
            routes.MapRoute(
               name: "GetStudentName",
               url: "{controller}/{action}/{name}",
               defaults: new { controller = "Home", action = "Index", name = UrlParameter.Optional }
           );
        }
    }

从教程中，我已经评论了WebApiConfig文件的那些行：

config.MapHttpAttributeRoutes();

            //config.Routes.MapHttpRoute(
            //    name: "DefaultApi",
            //    routeTemplate: "api/{controller}/{id}",
            //    defaults: new { id = RouteParameter.Optional }
            //);
            var json = config.Formatters.JsonFormatter;
            json.SerializerSettings.PreserveReferencesHandling = Newtonsoft.Json.PreserveReferencesHandling.Objects;
            config.Formatters.Remove(config.Formatters.XmlFormatter);

我创建了一个html文件，其中我放置了应用程序的所有URL，这是针对学生的名称选择：

<h4>Students</h4>
<a href="api/Students/sam" target="_blank">(GET => api/Students/sam) GetByName &raquo;</a><br />

问题在于，当我尝试在导航器中录制http://localhost:50001/api/Students/sam时，我收到此错误：

"ExceptionType":"System.NullReferenceException"

所以我在StudentsController

中得到了查询变量null

感谢您的帮助：）

通过名称获取学生的System.NullReferenceException

0 个答案: