MVC NET 5链接模型保存到数据库但不加载

Question

我对.NET MVC 5相当陌生，主要来自PHP背景。我有一个带有List集合的'Project'模型。当我仅使用测试控制器将数据保存到集合中时，它将会保存到数据库中。

问题出现在我试图从该集合中取出信息时，因为它总是返回为空。

我的项目模型：

public class Project 
{ 
    public int ID { get; set; } 

    [Display(Name = "Project")] 
    public string ProjectNumber { get; set; } 

    [Display(Name = "Client")] 
    public string Client { get; set; } 

    [DataType(DataType.MultilineText)] 
    public string Description { get; set; } 

    [Display(Name = "Start Date")] 
    [DisplayFormat(DataFormatString = "{0:d}", ApplyFormatInEditMode = true)] 
    public DateTime StartDate { get; set; } 

    [Display(Name = "Required Date")] 
    [DisplayFormat(DataFormatString = "{0:d}", ApplyFormatInEditMode = true)] 
    public DateTime RequiredDate { get; set; } 

    public string ProjectManagerId { get; set; } 

    [ForeignKey("ProjectManagerId")] 
    [Display(Name = "Project Manager")] 
    public ApplicationUser ProjectManager { get; set; } 

    [Display(Name = "Project Members")] 
    public int[] ProjectMembers { get; set; } 

    [Display(Name = "Tasks")] 
    public List<ProjectTask> TaskCollection { get; set; } 

} 

public class ProjectDb : DbContext 
{ 
    public ProjectDb() : base("DefaultConnection") 
    { 

    } 

    public DbSet<Project> Projects { get; set; } 
} 

我ProjectTask型号： 公共类ProjectTask {

public int Id { get; set; } 

    public int ProjectId { get; set; } 

    [ForeignKey("ProjectId")] 
    public virtual Project Project { get; set; } 

    public string Name { get; set; } 

    public string Description { get; set; } 

    public string TaskNotes { get; set; } 

    [DisplayFormat(DataFormatString = "{0:d}", ApplyFormatInEditMode = true)] 
    public DateTime StartDate { get; set; } 

    [DisplayFormat(DataFormatString = "{0:d}", ApplyFormatInEditMode = true)] 
    public DateTime DueDate { get; set; } 

    public int Duration { get; set; } 

    public TaskStatus Status { get; set; } 

    public TaskAlertLevel AlertLevel { get; set; } 

    public List<ProjectTask> SubTasks { get; set; } 

    public string Progress { get; set; } 
} 


public class ProjectTaskDb : DbContext 
{ 
    public ProjectTaskDb() : base("DefaultConnection") 
    { 

    } 

    public DbSet<Project> ProjectTasks { get; set; } 
} 

我的控制器，我只是想多看少空例外以外的东西：

public ActionResult DetailTasks(int? id) 
    { 
     if (id == null) 
     { 
      return new HttpStatusCodeResult(HttpStatusCode.BadRequest); 
     } 

     Project project = db.Projects.Find(id); 

     if (project == null) 
     { 
      return HttpNotFound(); 
     } 

     var tasks = project.TaskCollection; 

     ViewBag.tasks = tasks; 
     return View(project); 

    } 

希望它是索姆完全明显和愚蠢的东西，现在逃脱了我！

Answer 1

道歉的问候的意见，由于某种原因，我还以为你有问题加载最初的项目对象。所以看你的项目实体已延迟加载关闭，因为你不使用虚拟关键字：

public List<ProjectTask> TaskCollection { get; set; } 

VS

public virtual List<ProjectTask> TaskCollection { get; set; } 

当你这样做，你必须明确地或急切加载TaskCollection

Exlicitly负载：

​​

热切负载：

Project project = db.Projects.where(a => a.ID == id).Include(b => b.TaskCollection).FirstOrDefault(); 

p.s.你可能不得不和我的背景一起玩，因为我不在我可以加载的地方VS

Answer 2

嗨，你可以改变这一行试试：var tasks = project.TaskCollection;喜欢这样的：var tasks = project.TaskCollection.ToList();，它可以帮助你

完整的示例/更改代码：

public ActionResult DetailTasks(int? id) 
    { 
     if (id == null) 
     { 
      return new HttpStatusCodeResult(HttpStatusCode.BadRequest); 
     } 

     Project project = db.Projects.Find(id); 

     if (project == null) 
     { 
      return HttpNotFound(); 
     } 

     var tasks = project.TaskCollection.ToList(); 

     ViewBag.tasks = tasks; 
     return View(project); 

    } 

我相信这个时候你不会得到空的该项目.TaskCollection，如果数据库中的数据可用。

希望将上述信息是有用的，请让我知道你的想法或反馈

感谢

KARTHIK