如何在NHibernate中插入引用外鍵的子元素？

Question

我對流利NHibernate還是個新手。不知道我應該如何處理這個問題。

我有兩個實體：

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>(); 
    } 
} 

和映射是：

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(); 

    } 
} 

當我試圖儘可能插入：

 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); 

它給我的錯誤是：

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

Answer 1

當您創建新學生時，您需要設置Department不僅僅是Id。您是否有理由爲此需要單獨的財產？我會從你的實體和你的映射類中刪除這個屬性，並留在Department引用中。如果你需要Department Id，你可以通過Student.Department.Dept_id來引用它。

基本上你試圖在外鍵列中插入一個空值的實體。你會需要你的創作改變這樣的事情：

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); 

Answer 2

如果你會做這就像在你的職位，因爲您要發送Department對象的空數據，你會得到一個錯誤。正如Cole W所說。您需要將要添加的部門的ID與數據庫中現有部門的ID進行比較。

我將從Cole W answer中定義SelectedDepartment。您可以將其添加到存儲庫。

//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