+972 52-548-6969
How NHibernate forced me to OO design
time to read 1 min | 120 words
At some point of my code, I had this method.
Remember, this is spike code, so I didn't care for breaking things like encapsulation or getting ugly code. In essence, the code above is breaking encapsulation and stomps all over DRY and Liskov substitution principle.
It worked for a while, then it stopped. The reason that it stopped is that I started passing it lazy instances. And a lazy instance is a proxy, which is neither an ImageItem or HtmlItem. So now ContentItem has the following:
As an aside, notice the RecordApperances method. That is the absolute top of Ask, don't tell.
Comments
Heh, that should read "Tell, don't ask" :)
I wonder, what DisplayInformation looks like. Do you use it like:
if(info.IsImage) {
...
} else {
...
}
I have a similar problem with base classes and proxies, but mine also involves sublassing with discriminators.
The setup is following:
base class A, has Lazy=true, subclasses A1, A2 & A3 (table-per-class pattern - one table with columns for all class tree), discriminator field named e.g. "ASubClass"
class B has some property of type A (e.g. "myA")
Now, I am trying to do the following:
B myB = B.FindOne(.....);
A myA = B.myA;
if (myA.ASubClass == "1") //1 is discriminator value in subclass A1
{
}
Now, the line marked as Error, yields an "cannot cast NhibernateProxy to A1" exception - similarly to what you wrote in this post, the actual "myA" is an NHibernateProxy subclassing class A. However, it should rather be an proxy subclass of A1... Frankly speaking, I don't know how to go around this... How to cast the lazy initialized object to its subclass? I do not fully understand the solution that you gave here, Ayende :(
Comment preview