Red Hat Web Application Framework 6.1 Manual do Utilizador descarregar pdf (Página 98)

84 Chapter 9. Persistence Tutorial

select article_id

from authors, author_article_map

where authors.author_id = author_article_map.author_id

and lower(last_name) like :lastName || ’%’

} map {

authorID = authors.author_id;

}

query retrieveSelectedArticles {

BigDecimal articleID;

String title;

do {

select article_id, title from articles

} map {

articleID = articles.article_id;

title = articles.title;

}

Next, simply retrieve one query and add the other query as part of the ﬁlter, as follows (remove the \

and make it all one line):

Session session = SessionManager.getSession();

DataQuery query = \

session.retrieveQuery("tutorial.retrieveSelectedArticles");

Filter filter = query.addInSubqueryFilter("articleID", \

"tutorial.retrieveAuthorsWithParam");

// we have to set the value for "lastName" since it is a bind variable

// in the subquery we added.

filter.set("lastName", "b");

System.out.println\

("The following articles have at least one author whose " +

"last name starts with ’b’");

while (query.next()) {

System.out.println(query.get("title"));

}

The code above will actually execute the following SQL:

select article_id, title from articles

where article_id in (select article_id

from authors, author_article_map

where authors.author_id = \

author_article_map.author_id

and lower(last_name) like ? || ’%’

with ? = "b"

Note

While there are other, possibly better ways to obtain the same result, this example is used to demon-

strate how the feature works, not as an authoritative example of writing queries.

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