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Path Expression

 
Deepika Joshi
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EJB 3 in Action, end of page 360 & starting of 361

You can navigate further to other persistence fields or association fields using
a single-value path expression. For example, say we have a many-to-one relationship
between Category and User; we can navigate to a persistence field such as
firstName using association field user as follows:

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c.items.user.firstName


We may also want to navigate to the association field contactDetails to use its
e-mail address:

1
c.items.user.contactDetails.email

While using path expressions, keep in mind that you cannot navigate through the
collection-value path expressions to access a persistence or association field as in
the following example:

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c.items.itemName or c.items.seller

This is due to the fact you cannot access an element of a Collection, and items is
in fact is a collection of items. Using c.items.itemName in JPQL is similar to using

category.getItems().getItemName(), and this is not allowed.

Doubt:
I am not able to understand difference between two cases....
c.items.user is valid
c.items.seller is not valid
Please share your thoughts (interperate in your words).....

thanks....
 
Hong Anderson
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Deepika Joshi wrote:
Doubt:
I am not able to understand difference between two cases....
c.items.user is valid
c.items.seller is not valid
Please share your thoughts (interperate in your words).....

thanks....

To me, there is no different in these 2 cases.
 
Raf Szczypiorski
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There is a mistake in the 1, the book has a mistake. Have you checked the errata:
http://www.manning.com/panda/excerpt_errata.html
You can find this problem there, just do a search for "360".
 
Hong Anderson
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Thanks for errata list, I was thinking to see it.
 
Deepika Joshi
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I also thought that 1. is not correct, and wanted to confirm it.
thanks for EJB 3 in action correction page.....
 
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