Problem in a one-to-many relationship

BRRRRRRRR · **Posted:** Tue Aug 23, 2005 6:24 am

Hi folks,

I have a problem with a one-to-many relationship :

I have 2 classes Transactions and TransationLines

Code:

  public class TransactionInfo
   {
      public TransactionInfo()
      {
         Lines = new ArrayList();
      }

      public Int32 Id;
      public string CommentTop;
      public string CommentBottom;
      ...

      [XmlArray("Lines"), XmlArrayItem(typeof(TransactionLineInfo))]
      public IList Lines;
   }
   
   public class TransactionLineInfo
   {
      public TransactionLineInfo()
      {
      }

      public Int32 Id;
      public int Quantite;
      public string Description;
      ...
   }
 

mapped as :

Code:

 
  <class 
   name="MyCompany.Modules.ModA.Models.Transactions.TransactionInfo, MyCompany.Modules.ModA.Models" 
   table="Transactions_Transactions">
    
    <id name="Id" column="TransactionId" type="Int32" unsaved-value="0">
      <generator class="native" />
    </id>
    
    <property name="CommentTop" type="String" />
    <property name="CommentBottom" type="String" />
   ....
    
    <bag name="Lines" table="TransactionLignes" cascade="all-delete-orphan" lazy="false" inverse="true">
      <key column="TransactionId" />
      <one-to-many class="MyCompany.Modules.ModA.Models.Transactions.TransactionLineInfo, MyCompany.Modules.ModA.Models" />
    </bag>

  </class>
  
  <class 
   name="MyCompany.Modules.ModA.Models.Transactions.TransactionLineInfo, MyCompany.Modules.ModA.Models" 
   table="Transactions_TransactionLignes">
   
    <id name="Id" column="TransactionLigneId" type="Int32" unsaved-value="0">
      <generator class="native" />
    </id>
    
    <property name="Quantite" type="Int32" />
    <property name="Description" type="String" />
    ...
  <!-- Note: the 'transactionId' column that is used to make the link between a Transaction and its lines is not mapped -->
  </class>

Let's take an example :

Code:

Transaction trx = new Transaction();
TransactionLine l1 = new TransactionLine();
trx.CommentTop = "....";
l1.Description = ".....";
trx.Lines.Add(l1);
session.Save(trx);

The problem is that 'trx' is saved, 'l1' is saved but the link between trx and l1 is not assigned in the database (ie table TransactionLine.TransactionId = null)
I checked the generated sql and saw that at no time nhibernate does the association between trx and l1.
Here is the sequence in the log:
- INSERT INTO Transaction ... trx's properties ....
- Get the new Trx'Id ("Natively generated identity...")
- Detects the cascades
- INSERT INTO TransactionLines ... l1's properties BUT NO REFERENCE TO TRANSACTIONID !! ....

I checked with and without "inverse=true", giving the same result.

Someone faced the same problem ?

Thx in advance and have a nice day.

michal · **Posted:** Tue Aug 23, 2005 8:00 am

Hi,
when using inverse="true" you need to map many-to-one relation in your child , for example <many-to-one name="parent" column="parent_id" not-null="true"/> (transactionId in your case) Also remeber that the "bags" are not recommended without inverse="true" (use "Set" if you decide to use inverse="false" - in other case the whole collection will be deleted and recreated with any data change)

Because it is not so obvious subject I strongly recommend "deep" reading chapter 8 of the docs http://nhibernate.sourceforge.net/h2.0.3-docs/reference/html/parent-child.html

BRRRRRR · **Posted:** Wed Aug 24, 2005 8:18 am

Thx for ur answer Michal :)

I set up the many-to-one thing, but came another problem.
To understand, let me explain you the architecture of the project :

- a UI that calls the webservices (no link with dal, model or bll)
- a webservice (CRUD methods for TransactionInfo objects)
- a BLL
- a DAL (that use NHibernate)
- a Model class that stores all entities class (ie TransactionInfo, TransactionLineInfo, etc.)

I set a many-to-one link, it means that I have to add a "Parent" property to TransactionLineInfo.

Since TransactionInfo and TransactionLineInfo are exposed by the webservice, I need to set a [XmlIgnore()] on the "Parent" property to avoid a loop of serialization/deserialization on these entities.

In the DAL, before saving the object, I ensure links are correct by
relinking (trx.line.Parent = trx)

It works very well (add, update), until the moment I delete a TransactionLine from a Transaction :
nhibernate doesn't generate a DELETE command (that I don't understand since I precised cascade="all-delete-orphan".
Here is the sequence:
1. UI gets Transaction (thus the TransactionLines too) by the webservice
2. UI removes a line from Transaction.Lines
3. UI sends the Transaction back to the webservice
4. -- go through the layers --
5. (DAL) ensure transaction <-> transactionLine links
6. (DAL) session.SaveOrUpdate(transaction)

-> the line removed is still present in the database, and still linked to the transaction (transactionLine.transactionId != null)

What am I doing wrong ?

michal · **Posted:** Thu Aug 25, 2005 5:24 am

Hi,
I don't know it so deeply but as far I know the collections (IList in your case) MUST be a "proxy" to let the nhibernate know that you are deleting sth from them. So in your case you are loosing this information durign XML serialization/deserialization between UI and WS. Please someone correct me if I am wrong.
But if it is true, you should consider redesigning this part - for example WS method "deleteLineFromtrans(trans_id,line_id)" , re-read trans (or Lock it with Session) on the server, so the collection will be a proxy again and then - delete the line here. Then use session.flush() (not SaveOrUpdate) to commit the deletion.
Good luck.