Hi,

I collected all my questions for Chapter 3 into one post. I hope this is not too much.

Slew of questions on Chapter 3:

1) Page 80, Controlling Insertion and updates.
“If the complete class is immutable, set mutable=”false” in the class mapping”

What is the point of doing this? Wouldn’t declaring all the member variables as final take care of this automatically just using regular Java rules? Or is this so that Hibernate won’t even try to load data twice for the same instance and cause exceptions to be thrown?


2) Page 93, Entity and value types.
”In effect, the persistence mechanism implements pass-by-value semantics for some classes.”

I am not sure I understand your term of “pass-by-value persistence.” Could you explain what you mean by that?


3) Page 97, Table per concrete class
”In figure 3.7, if the subclasses are all mapped to different tables, a polymorphic association to their superclass (abstract BillingDetails in this example) can’t be represented as a simple foreign key relationship.”

Why not? Could you explain?


4) Page 110, discussion regarding cascade=”save-update”
Page 111, bottom of the page, example showing cascade=”all-delete-orphan”.

Wouldn’t both “save-update” and “all-delete-orphan” make inverse=”true” not needed, superfluous attribute (if the other one is specified)? If no, why not?


Thanks,
NG

Hibernate can make some optimizations if you set the attribute. It's not about loading things twice (this will not happen, since the Session is a cache anyway). Read chapters 4 and 5.



The topic is discussed again in chapter 6.



Again, covered in more detail in chapter 6. It's quite easy to understand that it doesn't work if you look at the tables for this strategy.



inverse and cascade are not related at all. Read chapter 4 for cascade and chapters 3 and 6 for inverse.

My best advice is to read at least chapters 3, 4, 5, 6, and 7 to understand Hibernate's core concepts.

Your best advise is to read the entire book to understand concepts explained in chapter 3 and only then ask questions?

Ok. I AM going through the entire book anyhow, but I like to understand what I am reading as I read it, especially if there is no "..We'll explain it later in chapter so and so" next to something that the book states and I don't undestand 100%.

But fine, I'll believe you that I am just lacking the material of the entire book and after I read it I'll have the answers to my questions from chapter 3. Seems odd to organize the book this way though.

No problem. I'll be back with these questions if it's not clear at the end of the read.

Thanks,
NG