Hello, I'm using Hibernate 3 and already have a bunch of very simple one-class-per-table type stuff working, so I'm not 100% newbie (just 90% :-))

However, I'm having trouble grasping the difference between these three concepts -- any explaination would be helpful. Thanks in advance.

1. When do you use <join> versus a collection (e.g. <one-to-many>)?

2. What is the difference between collection of value types versus a collection of references to other entities? Specifically, from a cascading perspective.

3. Lastly, when do you use <composite-id>? I believe the answer is obvious here (i.e. db table is designed this way) but still wanted to hear people's thoughts here.

Thanks again.

1. Apples and oranges. <join> pulls a value from another table into the mapped class. Your object model can be fine grained, where you have more classes than tables (<component>), flat, where you have as many classes as tables (regular <class> mappings, one per table), or coarse grained, where you have more tables than classes (<join>).

2. I think a collection of components has the same semantics as a collection of entities mapped with cascade="all,delete-orphan"

3. I think you pretty much answered your own question there. <composite-id> is not nice to work with, avoid it if you can.