延迟、急切和显式加载在实体框架 5 中不起作用答案

【问题标题】：Lazy, Eager and Explicit loading is not working in Entity Framework 5延迟、急切和显式加载在实体框架 5 中不起作用
【发布时间】：2015-12-07 17:56:00
【问题描述】：

部门类：

public partial class Department
{
    public Department()
    {
        this.Courses = new HashSet<Course>();
    }

    public int DepartmentID { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Course> Courses { get; set; }

}

课程类别：

public partial class Course
{
     public Course()
     {
         this.Enrollments = new HashSet<Enrollment>();
         this.People = new HashSet<Person>();
     }

     public int CourseID { get; set; }
     public string Title { get; set; }
     public int DepartmentID { get; set; }
     public virtual Department Department { get; set; }

}

上下文：

如下启用延迟加载。

universityDBContext.Configuration.LazyLoadingEnabled = true;
universityDBContext.Configuration.ProxyCreationEnabled = true;

延迟加载在 Entity Framework 5 中不起作用。请帮助

【问题讨论】：

标签： entity-framework

【解决方案1】：

public partial class Department
{
    public Department()
    {
        this.Courses = new HashSet<Course>();
        this.Students = new HashSet<Student>();
    }

    public int DepartmentID { get; set; }
    public string Name { get; set; }
    public decimal Budget { get; set; }
    public System.DateTime StartDate { get; set; }
    public Nullable<int> InstructorID { get; set; }
    public byte[] RowVersion { get; set; }

    public virtual ICollection<Course> Courses { get; set; }
    public virtual ICollection<Student> Students { get; set; }
    public virtual Person Person { get; set; }
}

【讨论】：

【解决方案2】：

public partial class Course
{
    public Course()
    {
        this.Enrollments = new HashSet<Enrollment>();
        this.People = new HashSet<Person>();
    }

    public int CourseID { get; set; }
    public string Title { get; set; }
    public int Credits { get; set; }
    public int DepartmentID { get; set; }
    public byte[] rowversion { get; set; }

    [ForeignKey("Department")]
    public virtual Department Department { get; set; }
    public virtual ICollection<Enrollment> Enrollments { get; set; }
    public virtual ICollection<Person> People { get; set; }
}

【讨论】：

我编辑了我的答案，ForeignKey 属性应该在DepartmentID 之上
那么您的模型应该没问题，您可以发布您正在执行的查询吗？
masterEntities universityDBContext = new masterEntities(); universityDBContext.Configuration.LazyLoadingEnabled = true; universityDBContext.Configuration.ProxyCreationEnabled = true; var dep = universityDBContext.Departments； foreach (var course in dep) { Console.WriteLine(); }
每个部门可以有多门课程，你怎么可以只在dep中选择一门课程然后尝试将其写入控制台？你事先做了SelectMany 吗？编辑：var result = universityDBContext.Departments.SelectMany(d => d.Courses).ToList(); foreach(var course in result) Console.WriteLine(course.Title); 应该可以正常工作
此代码 universityDBContext.Departments 选择所有部门以及课程。这不应该是这样的。如果延迟加载正确实现，则只有在课程上完成迭代时才应加载课程