I'm using NHibernate 1.2 GA and I have a problem

My Order class has a few properties like this:

public virtual decimal Total
{
get {
decimal total = 0;
foreach (OrderItem item in OrderItems) {
total += item.Total;
}

total += ShippingCost;
total += Tax*total;

return total;
}

set { }
}

You can see that the Total property is calculated based on the OrderItems and other properties of the class. I'm coding the Total this way to avoid having to call a RecalculateTotal method any time a dependent orderItem or property changes.

The mapping for the property is:

<property name="Total" column="total" type="Decimal" not-null="true" />

I can get, insert, update and delete orders, but the problem is that when I get an order, even if I don't change it, it gets updated.

I think this is because of automatic dirty chechking.

The total is stored as decimal(8, 4) in a SQL Server 2005 DB. So when I create an order, if the Total was 1.353433, the value 1.3534 will be stored in the database.

When NHibernate loads the order, the Total returns 1.353433 but when NHibernate loaded the Total, it read 1.3534 from the database, so when the flushing happens, as the value does not match, it forces an update of the order.

Is there any way to avoid this update for my usage scenario?

When NHibernate loads the entity, the property's value is 1.3534 and this value is "remembered" by NHibernate so that when the session is flushed, it can do a dirty check to see if anything has been changed. When the getter returns 1.353433 even when nothing is changed, NHibernate thinks that the Total property has been changed. Therefore, it issue an update statement to the database.

There are a number of ways around that. The simplest (if you can accept it) is to round the number before you return it from the getter so it will be consistent with what actually got written to the database. Other methods are along the lines of creating a UserType or an interceptor.

I have thought of that solution, but it seems a bit hackish.

How would you do it with an interceptor?

Inherit from the EmptyInterceptor class and override the FindDirty method. See the API documentation of the IInterceptor interface for the precise semantics.

Actually, overriding OnFlushDirty() probably makes the implementation easier. You may want to explore both options (i.e. OnFlushDirty and FindDirty)

I have looked at OnFlushDirty, but it seems that after an entity has been marked as dirty, there is no way to clean it. This comments are in the OnFlushDirty method:

Note that all flushes end in an actual synchronization with the database, in which as the new currentState will be propagated to the object, but not necessarily (immediately) to the database.

So, I'll look into the FindDirty method for now. Thanks

BTW, It is a shame that there aren't any post events in the IInterceptor interface.

Thanks

Hi manunews,

Did you find a solution? If yes: could you post it here?

Thanks,


Pieter