Generics - Mapping Collections Example Please

gcook1@shaw.ca · **Joined:** Tue Feb 07, 2006 4:27 pm **Posts:** 69

I'm looking for a simple example of using a generic collection to map a one-to-many association using NHibernate 1.2.0 alpha 1.

What I Have now

Code:

    public class Invoice
    {
        private IList _LineItems;
    }

What I would like

Code:

    public class Invoice
    {
        private IList<LineItem> _LineItems;
    }

Any help would be great, as I'm not finding good documenation on this feature since it has been integrated.

Aaron_Murrell · **Joined:** Tue Aug 01, 2006 9:42 pm **Posts:** 6

Code:

    class Invoice
    {
        private IList<LineItem> _LineItems;

        public Invoice()
        {
            this._LineItems = new List<LineItem>();
        }

        public IList<LineItem> LineItems
        {
            get { return this._LineItems; }
            set { this._LineItems = value; }
        }
    }

Code:

    class LineItem
    {
        private Invoice _Invoice;

        public LineItem()
        {
        }

        public Invoice ParentInvoice
        {
            get { return this._Invoice; }
            set { this._Invoice = value; }
        }
    }

Code:

<class name="YourNamespace.Invoice, YourAssembly" table="Invoices">
  ...
  <bag generic="true" name="LineItems" inverse="true" cascade="all-delete-orphan">
    <key column="InvoiceID"></key>
    <one-to-many class="YourNamespace.LineItem, YourAssembly"/>
  </bag>
</class>

Code:

<class name="YourNamespace.LineItem, YourAssembly" table="LineItems">
  ...
  <many-to-one 
  name="Invoice" 
  column="InvoiceID" 
  class="YourNamespace.LineItem, YourAssembly" />
</class>

This should give you the right idea. Don't forget, just like any other bidirectional collection association you must maintain both sides in your object. ie

Code:

LineItem li = new LineItem();
Invoice1.LineItems.Add(li);
li.ParentInvoice = Invoice1;

gcook1@shaw.ca · **Joined:** Tue Feb 07, 2006 4:27 pm **Posts:** 69

Excellent. I have mapped these types of relationship before, I had no idea it was as easy as generic="true" to use generics with them.

Thanks

gert · **Joined:** Thu Jan 19, 2006 4:29 pm **Posts:** 348

gcook1@shaw.ca wrote:

Excellent. I have mapped these types of relationship before, I had no idea it was as easy as generic="true" to use generics with them.

Thanks

AFAIK, You should not need the generic="true"... They should work just "as is", use old mapping but the new generic IList<>. Did You have any problems with mapping generics?

Gert

gcook1@shaw.ca · **Joined:** Tue Feb 07, 2006 4:27 pm **Posts:** 69

So far things are working well. I've got the object mapped but I have yet to develop my mapping tests for it so I'm not using it right now.

NHibernate was happy with how it is mapped for now. I'll keep your suggestion in mind though if my mapping test for this association fails once I get the test developed.

Thanks

sergey · **Posted:** Wed Aug 16, 2006 8:13 am

NHibernate doesn't need generic="true", you can switch between generic and non-generic types without altering the mapping files.

PandaWood · **Joined:** Wed Oct 25, 2006 10:51 pm **Posts:** 71

Code:

<class name="YourNamespace.Invoice, YourAssembly" table="Invoices">
  ...
  <bag generic="true" name="LineItems" inverse="true" cascade="all-delete-orphan">
    <key column="InvoiceID"></key>
    <one-to-many class="YourNamespace.LineItem, YourAssembly"/>
  </bag>
</class>

Hi Aaron,

I was wondering why you use a 'bag' collection type. Just semantically speaking, since we're using a 'List' I would have thought you would use a <list> ?

Admittedly, while I'm looking at the documentation on collections (beta2), it's not yet clear to me what the difference is, or really exactly what a bag is.

But you can ignore that, I'm just hoping there's a sensible reason why you need something other than a <list> for a List.