Saving child collections with NHibernate
- by Ben
Hi,
I am in the process or learning NHibernate so bare with me.
I have an Order class and a Transaction class. Order has a one to many association with transaction. The transaction table in my database has a not null constraint on the OrderId foreign key.
Order class:
public class Order {
public virtual Guid Id { get; set; }
public virtual DateTime CreatedOn { get; set; }
public virtual decimal Total { get; set; }
public virtual ICollection<Transaction> Transactions { get; set; }
public Order() {
Transactions = new HashSet<Transaction>();
}
}
Order Mapping:
<class name="Order" table="Orders">
<cache usage="read-write"/>
<id name="Id">
<generator class="guid"/>
</id>
<property name="CreatedOn" type="datetime"/>
<property name="Total" type="decimal"/>
<set name="Transactions" table="Transactions" lazy="false" inverse="true">
<key column="OrderId"/>
<one-to-many class="Transaction"/>
</set>
Transaction Class:
public class Transaction {
public virtual Guid Id { get; set; }
public virtual DateTime ExecutedOn { get; set; }
public virtual bool Success { get; set; }
public virtual Order Order { get; set; }
}
Transaction Mapping:
<class name="Transaction" table="Transactions">
<cache usage="read-write"/>
<id name="Id" column="Id" type="Guid">
<generator class="guid"/>
</id>
<property name="ExecutedOn" type="datetime"/>
<property name="Success" type="bool"/>
<many-to-one name="Order" class="Order" column="OrderId" not-null="true"/>
Really I don't want a bidirectional association. There is no need for my transaction objects to reference their order object directly (I just need to access the transactions of an order). However, I had to add this so that Order.Transactions is persisted to the database:
Repository:
public void Update(Order entity)
{
using (ISession session = NHibernateHelper.OpenSession()) {
using (ITransaction transaction = session.BeginTransaction()) {
session.Update(entity);
foreach (var tx in entity.Transactions) {
tx.Order = entity;
session.SaveOrUpdate(tx);
}
transaction.Commit();
}
}
}
My problem is that this will then issue an update for every transaction on the order collection (regardless of whether it has changed or not).
What I was trying to get around was having to explicitly save the transaction before saving the order and instead just add the transactions to the order and then save the order:
public void Can_add_transaction_to_existing_order()
{
var orderRepo = new OrderRepository();
var order = orderRepo.GetById(new Guid("aa3b5d04-c5c8-4ad9-9b3e-9ce73e488a9f"));
Transaction tx = new Transaction();
tx.ExecutedOn = DateTime.Now;
tx.Success = true;
order.Transactions.Add(tx);
orderRepo.Update(order);
}
Although I have found quite a few articles covering the set up of a one-to-many association, most of these discuss retrieving of data and not persisting back.
Many thanks,
Ben
