导航属性未加载

Question

我正在使用objectDataSource填充gridview 。 我有2个简单的课程：

public class Employee
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Gender { get; set; }
    public int Salary { get; set; }
    public Department Department { get; set; }

}

和

public class Department
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Location { get; set; }
    public List<Employee> Employees { get; set; }
}

我也有

public class EmployeeDBContext : DbContext
{
    public DbSet<Department> Departments { get; set; }
    public DbSet<Employee> Employees { get; set; }

}

现在在我的EmployeeRepository类中

public List<Department> GetDepartments()
{
    EmployeeDBContext employeeDBContext = new EmployeeDBContext();
    return employeeDBContext.Departments.Include("Employees").ToList();
}

即使我添加了.Include（“ Employees”） ，在gridview中也缺少员工。 我在这里做错了什么？

Answer 1

首先，您需要在Employee类中具有一个外键（DepartmentId） 。 我不知道视频是如何解决的。

public class Employee
{
    public int Id { get; set; }
    public int DepartmentId { get; set; } <=====
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Gender { get; set; }
    public int Salary { get; set; }
    public virtual Department Department { get; set; }
           ^^^^^^^
}

public class Department
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Location { get; set; }
    public virtual ICollection<Employee> Employees { get; set; }
           ^^^^^^^^^^^^^^^^^^
}

public partial class EmployeeDBContext : DbContext
{
    public virtual DbSet<Employee> Employee { get; set; }
    public virtual DbSet<Department> Department { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        // Optional, but good practice to have the mapping here. 
        modelBuilder.Entity<Department>()
            .HasMany(e => e.Employee)
            .WithRequired(e => e.Department)
            .HasForeignKey(e => e.DepartmentId);
    }
}

- 要么 -

将DepartmentId属性和[ForeignKey]数据注释添加到Department。

public class Employee
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Gender { get; set; }
    public int Salary { get; set; }    
    public int DepartmentId { get; set; } <=== 

    // Optional, but good practice to have this data annotation attribute. 
    [ForeignKey("DepartmentId")] <=== 
    public Department Department { get; set; }
}

仅供参考：您想使用虚拟的，以防将来有人要使用延迟加载。

Answer 2

你尝试过这样的事情吗

return employeeDBContext.Departments.Include(x =>x.Employees ).ToList(); ？