Hi,

I cannot find any example from doc, so I am asking this here. This may be
very simple for you guys, please bear with me.

I try to do a join based on multiple tables, for example: if I have
a Book table, and a User table, a Book can have multiple users, and they have one-to-many bidirectional association. That mean User table can have a FK which is identical to PK of Book. In SQL, I can do something like the following to retrieve all user names of one book:

select user.name from Book book, User user where user.book_id = book.book_id;

How can we do the above in HQL? Thanks.

Assuming you have this "one-to-many bidirectional association" mapped something like:


Then the HQL would be:
select u.name from User as u where u.book.id=:bookId
to retreive just the user's name attribute, or:
from User as u where u.book.id=:bookId
to retreive the entire User instance

I think I may have figure it out as following:

select user.name from User user where user.book.boo_id = ?

It means to retrieve all user names based on a given book id,
is this correct, need you guys confirmation.

I am assuming that "boo_id" is the column name? Don't do that. HQL deals with your java object model, not the relational model.

Thanks, Steve. Your explanations make my probelm go away.

You are right, Steve. That should be Id attribute of Book object, not the column name. I guess :bookId in your query example is assuming Book has a Id attribute, is that correct?

It seems Hibernate is really powerful!

:bookId is what is called a "named parameter". Much nicer than the '?' version. Hibernate also supports the '?' form if you feel more comfortable with that.

So either:


or

Steve illustrates a valid reason to use his first example rather than the second as the index starts at 0 rather than 1. This issue is avoid by using named parameters.