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Inner Join

Deepika Joshi
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Joined: Feb 24, 2009
Posts: 268
EJB 3 in Action, page 377

Category & User entities have many-to-one association. To retrieve all user that match a specific criterion we could try this query:




I think its correct in book.... there is no way to delete the post... so please ignore this doubt....
Reza Rahman
author
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Joined: Feb 01, 2005
Posts: 580
    
    5
Deepika,

It is a poorly constructed inner join example. The inner join in this case really serves no function. This is in my list to fix for the second edition.

Thanks,
Reza


Independent Consultant — Author, EJB 3 in Action — Expert Group Member, Java EE 6 and EJB 3.1
Hong Anderson
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Joined: Jul 05, 2005
Posts: 1936

Just want to make it clear. Should "u.Category c" be "Category c"?
Or "u.Category c" is correct syntax?

But why don't you use "u.category c"? (I guess category is a property of User entity).


SCJA 1.0, SCJP 1.4, SCWCD 1.4, SCBCD 1.3, SCJP 5.0, SCEA 5, SCBCD 5; OCUP - Fundamental, Intermediate and Advanced; IBM Certified Solution Designer - OOAD, vUML 2; SpringSource Certified Spring Professional
Deepika Joshi
Ranch Hand

Joined: Feb 24, 2009
Posts: 268
Just want to make it clear. Should "u.Category c" be "Category c"?
Or "u.Category c" is correct syntax?

But why don't you use "u.category c"? (I guess category is a property of User entity).

I had the same doubt & finally imagined that Category is property of User.... (as in description it says Many-to-One relationship in Entities)
(for author) No offense, but JPQL examples could b easy to understand if corresponding (native) SQL is also given in the book....
I have completed the chapter (JPQL) but I do not have confidence, is there any link for JPQL for some other source.....


thanks...
Reza Rahman
author
Ranch Hand

Joined: Feb 01, 2005
Posts: 580
    
    5
Deepika,

There is no offense taken. I don't think the JPQL chapter is particularly strong either. You could try the Mike Keith book centered on JPA only.

Regards,
Reza
 
It is sorta covered in the JavaRanch Style Guide.
 
subject: Inner Join