So, while I'm pretty sure I would use the descriminator construct to do this, I'm just not sure how.

Basically I have one table, comments, that has a column that links to multiple tables based on a type column within comments. IE: If comments_type is 'blog' then the reference_id is a foreign key of the blog table. If the comments_type is 'pictures' then the reference_id is a foreign key of the media table, and so on and so forth.

For java I'm simply going to use inhertance to make them all have the same standard media properties (including id) and generics to instantiate the comment class with the appropriate media class. But I'm just not sure how to translate this when mapping, or how to tell hibernate which class to use for the generic comment class (or if I can use a generic comment class for that matter).

Any help would be appreciated as I couldn't find any examples of this...the only I found with discriminators didn't fit my situation at all.

Hi jojo46,

You could do it by bag. But for that you should have separate PK for each table. or what you can do ,use different range of PK for comments parent table.

Avoid this type of design

Actually, I'm not sure if I explained it right. There isn't a parent table of comment. Comment has a many to one relation to it's reference's (blog, media, etc). The comment for every type of reference is identical, there is no different between them.

While I know my alternative (realistic one) is to create an intermediate table for each reference type possible, that would break the many to one relation (making it many to many) and it would produce a lot of little tables everywhere which aren't needed. My preference is to keep it a many to one relation, and since I'll know what comment type I want based on the context of the user's actions, this seems like a fairly straight forward approach to me with no waste.

For the java I'll be instantiating the comment class w/ generics, so it'll be something like

Comment<Blog> blogComment = new Comment<Blog>();

which will tell the class to use a blog for the reference class. With generics, it seems much better to use the proper class in comment rather then have five of them, four of which aren't being used (plus I don't think you could do that anyway since they would relate to the same column). One of my questions was whether or not Hibernate could deal w/ generics in this way...I'm hoping it can since generics are so powerful, and keep things very organized.

Hopefully that explains better what I have in mind.