HQL

With Hibernate, you can define an HQL query in a Hibernate mapping file (hbm. xml) and give it a name.

Listing 2 demonstrates two methods: a group lookup using an HQL query and a group lookup followed by an action.

Of course, not many of us would need (or want, for that matter) to retrieve the entire database with a single HQL query.

But HQL does enable you to pass native queries to your underlying database.

The only exception is when your application has special business rules for data aggregation and ordering that HQL doesn't support.

You can build a HQL WHERE clause using either binding parameters or simple string concatenation; the decision impacts on performance.

To access an Individual from the database, simply specify the class name in your HQL query, as shown in Listing 5.

Added support for calling Sql Functions (HQL concept) from projections (Criteria).

This can be overridden with an eager fetching, such as join fetching using HQL or Criteria, when you need data from both entities.

As of now, sharding framework cannot be used with HQL. It can only be used with SQL.

For information on externalizing HQL queries, refer to the Resources section.

From the WHERE clause in HQL you can usually guess the corresponding SQL WHERE clause.

We tuned an HQL query to select electricity deals from about 30 seconds to less than 1 second.

But our supporting example will use HQL exclusively.

You ll work entirely with HQL in the examples that follow.

I ll use only HQL in the examples for this article.

HQL is quite simple to use.

Listing 17 illustrates a way to retrieve the entire database using a two-word HQL query.

You should avoid embedding HQL queries in your Java code unless they are truly dynamic queries.

We can use this abstract superclass in our HQL queries, as shown in Listing 14.

If your HQL or Criteria returns a lot of data, you should take care of two things