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  • Book Overview & Buying EJB 3 Developer Guide
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EJB 3 Developer Guide

EJB 3 Developer Guide

By : Michael Sikora
4.2 (6)
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EJB 3 Developer Guide

EJB 3 Developer Guide

4.2 (6)
By: Michael Sikora

Overview of this book

Table of Contents (18 chapters)
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EJB 3 Developer Guide
Credits
About the Author
About the Reviewers
Preface
1
Annotations and Their Corresponding Packages

Joins


The queries in the previous section performed an implicit join. A join occurs whenever we need to navigate across two or more entities. We have seen that we cannot construct a composite path expression from a collection association-field. This prevents us from navigating across a one-to-many or many-to-many entity relationship. We can do this explicitly using one of the JOIN operators.

Inner Joins

Take a look at the following query:

SELECT c.lastName, a.addressLine FROM Customer c
INNER JOIN c.addresses a

For each customer this will retrieve their last name and all associated address lines (recall a customer can have more than one address in our model). The identification variable a is defined by the path expression c.addresses, and this identification variable is used in the expression a.addressLine. In the case of an inner join, if a customer does not have an address then the customer's last name will not be retrieved by the above query. Note that the use of the keyword INNER is optional...

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83
Tech Concepts
36
Programming languages
73
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EJB 3 Developer Guide
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