I have a table with a primary key in the format M001, M002 etc (lets not think about what happens after M999 for now). I’m using Hibernate Annotations, and I found a great way of generating the Primary Key value for new Records:
First I created a database sequence to use. Then I implemented org.hibernate.id.IdentifierGenerator;
public class StockCodeGenerator implements IdentifierGenerator {
private static Logger log = Logger.getLogger(StockCodeGenerator.class);
public Serializable generate(SessionImplementor session, Object object)
throws HibernateException {
String prefix = "M";
Connection connection = session.connection();
try {
PreparedStatement ps = connection
.prepareStatement("SELECT nextval ('seq_stock_code') as nextval");
ResultSet rs = ps.executeQuery();
if (rs.next()) {
int id = rs.getInt("nextval");
String code = prefix + StringUtils.leftPad("" + id,3, '0');
log.debug("Generated Stock Code: " + code);
return code;
}
} catch (SQLException e) {
log.error(e);
throw new HibernateException(
"Unable to generate Stock Code Sequence");
}
return null;
}
}
Then, in my entity class, I simply annotate the id field like this:
@Id
@GenericGenerator(name="seq_id", strategy="my.package.StockCodeGenerator")
@GeneratedValue(generator="seq_id")
@Column(name = "stock_code", unique = true, nullable = false, length = 20)
public String getStockCode() {
return this.stockCode;
}
It works really well!
[Thanks to Jejomar Dimayuga for this post http://blog.dagitab.com/htsrv/trackback.php?tb_id=30 which I have modified slightly to use a sequence rather than a table]