Saving collections of an object

JackBigMac · **Joined:** Tue May 17, 2005 2:48 pm **Posts:** 47

I have an employee object which has a list of EmployeeProject objects. This object indicates which employee is involved in which project. It has an Employee property and a Project property.
The user can select a project in a listbox and add it to another listbox with involved projects. The project is added to the employee like this:

Code:

private void btnAdd_Click(object sender, System.EventArgs e)
{
   ListItem item = lbxProjects.SelectedItem;
   if (item != null)
   {
           EmployeeProject proj = new EmployeeProject();
      proj.Employee = _employee;
      proj.Project= (Project)MyUtils.GetObjectById(typeof(Project), Int32.Parse(item.Value));
      _employee.Projects.Add(proj);

      lbxEmployeeProjects.Items.Add(item);
      item.Selected = false;
   }
}

But when I save the employee, the EmployeeProject objects are not saved to the database. I guess my mapping file isn't correct yet for the EmployeeProject collection:

Code:

<bag name="Projects" table="employeeproject" lazy="true">
   <key column="employeeid"/>
   <one-to-many class="MyApp.Core.Domain.EmployeeProject, MyApp.Core"/>
</bag>

What do I need to do to save the EmployeeProject objects?

martijnb · **Joined:** Sat May 14, 2005 8:40 am **Posts:** 130

You have to add a cascade attribute to your bag collection and remove the table attribute if the relation is a one-to-many.

Code:

BTW, if your EmployeeProject class does nothing more than connection Employees and Projects you might consider removing this class and add an IList of Projects directly to the Employee. This is a many-to-many relation and looks as follows:

Code:

<bag name="Projects" table="employeeprojects" cascade="none" lazy="true">
    <key column="employeeid" />
    <many-to-many class="MyApp.Core.Domain.Project, MyApp.Core" column="projectid"  />
</bag>

JackBigMac · **Joined:** Tue May 17, 2005 2:48 pm **Posts:** 47

Thanks Martijn,

I will try this tonight. But what does the 'lazy' element?

martijnb · **Joined:** Sat May 14, 2005 8:40 am **Posts:** 130

The lazy element means that the collections is only fetched from the database when accessed. See also http://nhibernate.sourceforge.net/h2.0. ... tions-s1-7 .

JackBigMac · **Joined:** Tue May 17, 2005 2:48 pm **Posts:** 47

The last time I solved my problem by removing the EmployeeProject class and defining a many-to-many relation between employees and projects.
I'm now in the situation that I have to make a separate class. Instances of this class don't get saved into the database. This is the bag in the mapping file of the Employee class:

Code:

<bag name="EmployeeProjects" cascade="all" lazy="true">
  <key column="employeeid"/>         
  <one-to-many class="MyApp.Core.Domain.EmployeeProject, MyApp.Core"/>
</bag>

What am I doing wrong?

Regards,
JackBigMac

Patrik.H · **Posted:** Thu Jul 28, 2005 1:42 am

Hi

Im not sure this will solve it but try adding inverse=true to your mapping files for the bag.

<bag name="Projects" table="employeeproject" lazy="true" inverse="true">