如何在 NHibernate 中插入引用外键的子元素？

Question

我对 Fluent NHibernate 还很陌生。不知道我应该如何处理这个问题。

我有两个实体：

 public class Student
{
    public virtual Guid StudentId { get; set; }
    public virtual String Dept_id { get; set; }
    public virtual String Name { get; set; }
    public virtual int Age { get; set; }
    public virtual String Address { get; set; }

    public virtual Department Department { get; set; }
}
public class Department
{
    public virtual int Dept_id { get; set; }
    public virtual String Dept_name { get; set; }
    public virtual IList<Student> Students { get; set; }

    public Department()
    {
        Students = new List<Student>();
    }
}

并且映射是：

public class DepartmentMap : ClassMap<Department>
{
    public DepartmentMap()
    {
        Table("Department");
        Id(x => x.Dept_id).Column("Dept_id");
        Map(x => x.Dept_name).Column("Dept_name");

        HasMany(x => x.Students).KeyColumn("Student_id").Inverse()
            .Cascade.All();
    }
}
public class StudentMap :ClassMap<Student>
{
    public StudentMap() 
    {
        Table("Student");
        Id(x => x.StudentId).Column("Student_id").GeneratedBy.GuidComb();
        Map(x => x.Name);
        Map(x => x.Age);
        Map(x => x.Address);
        Map(x => x.Dept_id).Column("Dept_id");

        References(x => x.Department).Column("Dept_id").Not.Nullable();

    }
}

当我尝试插入为：时，

        StudentRepository rep = new StudentRepository();
        Student s = new Student();
        s.Name = txtname.Text;
        s.Age = int.Parse(txtage.Text);
        s.Address = txtaddress.Text;
        s.Dept_id = dddept.SelectedItem.Value;
        rep.Add(s);

它给我的错误为：

{"not-null property references a null or transient value nHibernateTest.Domain.Student.Department"}

Answer 1

如果您像帖子中那样这样做，您将收到错误，因为您想发送 Department 对象的空数据。正如科尔·W 所说。您需要将要添加的部门的 ID 与数据库中现有部门的 ID 进行比较。

我将从 Cole W 答案中定义 SelectedDepartment。您可以将其添加到存储库。

//repository
public Department SelectedDepartment(int id)
{
Department getDepartment = session.Get<Department>(id);
return getDepartment;
}
//controller
 s.Department = rep.SelectedDepartment(1) //for example department with id = 1

Answer 2

当您创建新学生时，您需要设置部门而不仅仅是 ID。您是否有理由为此需要一个单独的财产？我会从您的实体和映射类中删除此属性，然后保留部门引用。如果您需要部门 ID，您可以通过 Student.Department.Dept_id 引用它。

基本上，您正在尝试在外键列中插入具有空值的实体。您需要将您的创作更改为如下所示：

    StudentRepository rep = new StudentRepository();
    Student s = new Student();
    s.Name = txtname.Text;
    s.Age = int.Parse(txtage.Text);
    s.Address = txtaddress.Text;
    s.Department = SelectedDepartment;  //SelectedDepartment is the actual department entity from the database
    rep.Add(s);