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Hibernate: HQL in Depth


SQL can be combined with an object-oriented approach. What we end up with is Hibernate Query Language, or HQL. This article discusses how HQL works, and shows how to use it in the real world.

Author Info:
By: A.P.Rajshekhar
Rating: 4 stars4 stars4 stars4 stars4 stars / 86
January 10, 2006
TABLE OF CONTENTS:
  1. · Hibernate: HQL in Depth
  2. · HQL: Understanding Queries
  3. · HQL in the Real World
  4. · Points to Remember

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Hibernate: HQL in Depth - Points to Remember
(Page 4 of 4 )

There are some points to be kept in mind when working with HQL. They are as follows:

1. Queries are case insensitive, barring the Java class and propertiesí names. Hence SELECT and select are the same, but Order and order are not.

2. If the class or package does not find a place in imports, then the objects have to be called with the package name. For example, if com.someorg.persist.Order is not imported, then the query would be from com.someorg.persist.Order and so on.

3. A query like

    from Foo foo where foo.bar.baz.customer.address.city is
not null

would translate into a SQL query with four joins. So such queries should be used when absolutely necessary, as joins cost heavily in terms of memory and processing.

Thatís all for this discussion. In the future I would be covering Criteria queries and advanced HQL. Till then.


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