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to the properties of particular instances. You wouldn t want the details of this naming scheme to be exposed to the user; instead, native SQL queries are specified with placeholders for the column aliases. The following native SQL query shows what these placeholders the names enclosed in braces look like:

String sql = "select u.USER_ID as {uzer.id}," + " u.FIRSTNAME as {uzer.firstname}," + " u.LASTNAME as {uzer.lastname} from USERS u";

Each placeholder specifies an HQL-style property name. When we call this query in code, we must provide the entity class that is referred to by uzer in the placeholders. This tells Hibernate what type of entity is returned by the query:

List results = session.createSQLQuery(sql, "uzer", User.class).list();

If User is mapped to the USER table, it s verbose to respecify all the mappings from columns to properties in this way. Here s a shortcut:

List results = session.createSQLQuery("select {uzer.*} from USERS uzer", "uzer", User.class) .list();

The {uzer.*} placeholder is replaced with a list of the mapped column names and correct column aliases for all properties of the User entity. The name used in the placeholder must be the same name that is used as the table alias in the SQL query (uzer in this example). Note that the following variation works, but it isn t good style:

List results = session.createSQLQuery("select {users.*} from users", "users", User.class) .list();

In this case, there is no explicit table alias, so the implicit alias is the same as the table name users (note the lowercase). A native SQL query may return tuples of entities (as usual, Hibernate represents a tuple as an instance of Object[]):

List tuples = session.createSQLQuery( "select {u.*}, {b.*} from USERS u inner join BID b" + " where u.USER_ID = b.BIDDER_ID",

new String[] { "u", "b" }, new Class[] {User.class, Bid.class} ) .list();

You may also have named SQL queries separate from application code in your Hibernate mapping files. We use the <return> element to specify the query return types:

<sql-query name="findUsersAndBids"><![CDATA[ select {u.*}, {b.*} from USERS u inner join BID b where u.USER_ID = b.BIDDER_ID ]]> <return alias="u" class="User"/> <return alias="b" class="Bid"/> </sql-query>

Since the native SQL is tightly coupled to the actual mapped tables and columns, we strongly recommend that you define all native SQL queries in the mapping document instead of embedding them in the Java code. If, in some special cases, you need even more control over the SQL that is executed, or if you want to call a stored procedure using JDBC, Hibernate offers you a way to get a JDBC connection. A call to session.connection() returns the currently active JDBC Connection from the Session. It s not your responsibility to close this connection, just to execute whatever SQL statements you like and then continue using the Session (and finally, close the Session). The same is true for transactions; you must not commit or roll back this connection yourself (unless you completely manage the connection for Hibernate, without a connection pool or container datasource).

How do I execute a stored procedure with Hibernate In Hibernate 2.x, there is no direct support for stored procedures. You have to get the JDBC connection and execute the SQL yourself. However, direct stored procedure support was implemented for the next major Hibernate version at the time of writing. You will soon be able to map CUD operations for entities to stored procedures and directly call any stored procedure using a Hibernate API.

When you re writing queries and testing them in your application, you may encounter one of the common performance issues with ORM. Fortunately, we know how to avoid (or, at least, limit) their impact. This process is called optimizing object retrieval. Let s walk through the most common issues.