EF6不会延迟加载导航属性 [英] EF6 does not lazy load navigation property

问题描述

我有一个EF6懒加载的问题。我搜索了StackOverflow，但是我发现的其他问题并不适合我的情况。

我正在使用 virtual 关键字和我的类是 public 。 LazyLoadingEnabled 和 ProxyCreationEnabled 都设置为 true p>

当我从数据库加载课程对象时， presentationId 被设置为正确的 id 和演示文稿是 null 是正确的，因为它还没有加载。

当我将演示文稿属性传递给 PresentationsController.ToDto（）方法应该是延迟加载，但是我在方法中得到一个 null引用异常，因为它仍然是 null 。

我知道这些关系是有效的，因为当我强制加载在$ code code code code code code code code code code code code> public static CourseDto ToDto（Course item，DnbContext db）方法它被加载。见图：

如您所见， item.presentation 是 null ：

当我手动评估 db.courses.Find（257）.presentation 时，它引用与 item 对象，它们都被加载：

这是我的POCO：

  public abstract class BaseModel：ISoftDelete {
 public int id {get;组; 
} 
 
 public class课程：BaseModel {
 [必需] 
 public int presentationId {get;组; } 
 public virtual Presentation presentation {get;组; 
} 
  

我的Web API控制器方法：

  // GET api / Courses / 5 
 public CourseDto GetCourse（int id）{
 var item = db.courses.FirstOrDefault（x = > x.id == id）; 
返回ToDto（item，db）; 
} 
 
 public static CourseDto ToDto（课程项目，DnbContext db）{
 var dto = new CourseDto（）; 
 
 if（item.presentationId> 0）dto.presentation = PresentationsController.ToDto（item.presentation，db）; 
 
 return dto; 
} 
  

任何想法？

解决方案

如果要通过动态代理使用延迟加载，实体必须明确声明为公共构造函数。 （如果你有其他参数）

  public abstract class BaseModel：ISoftDelete {
 public BaseModel（）{} 
 public int id {get;组; } 
 
 public class课程：BaseModel {
 public Course（）{} 
 [必需] 
 public int presentationId {get;组; } 
 public virtual Presentation presentation {get;组; } 
} 
  

I'm having an issue with EF6 lazy loading. I've searched StackOverflow, but the other questions I've found doesn't fit my case.

I'm using the virtual keyword and my classes are public. LazyLoadingEnabled and ProxyCreationEnabled are both set to true.

When I load a course object from the db, presentationId is set to the correct id and presentation is null which is correct, because it hasn't been loaded yet.

When I pass the presentation property to the PresentationsController.ToDto() method it should be lazy loaded, but I get a null reference exception inside the method because it's still null.

I know that the relationships are working because when I force load the presentation property of a course in the Watch window with a break point at the public static CourseDto ToDto(Course item, DnbContext db) method it gets loaded. See images:

As you can see item.presentation is null:

When I manually evaluate db.courses.Find(257).presentation which is referencing the same presentation as the item object does, they're both loaded:

Here are my POCOs:

public abstract class BaseModel : ISoftDelete {
    public int id { get; set; }
}

public class Course : BaseModel {
    [Required]
    public int presentationId { get; set; }
    public virtual Presentation presentation { get; set; }
}

My Web API controller methods:

// GET api/Courses/5
public CourseDto GetCourse(int id) {
    var item = db.courses.FirstOrDefault(x => x.id == id);
    return ToDto(item, db);
}

public static CourseDto ToDto(Course item, DnbContext db) {
    var dto = new CourseDto();

    if (item.presentationId > 0) dto.presentation = PresentationsController.ToDto(item.presentation, db);

    return dto;
}

Any ideas?

解决方案

Entities must have explicitly declared public constructors if you want to use lazy loading via dynamic proxies. (If you have other with parameters)

public abstract class BaseModel : ISoftDelete {
    public BaseModel() { }
    public int id { get; set; }
}

public class Course : BaseModel {
    public Course() { }
    [Required]
    public int presentationId { get; set; }
    public virtual Presentation presentation { get; set; }
}

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