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Java Hibernate Query

Building a Hibernate Query

Java Hibernate query retrieves data with HQL expressions.

Introduction to Hibernate Query Language (HQL)

Hibernate Query Language (HQL) is an object-oriented query language, similar to SQL, but instead of operating on tables and columns, HQL operates on persistent objects and their properties. HQL is case-insensitive except for names of Java classes and properties.

HQL provides a powerful and flexible way to query the database while maintaining the object-oriented approach of Hibernate. Let's explore how to use HQL to retrieve data effectively.

Basic HQL Syntax

The basic syntax of HQL is similar to SQL. Here is the structure of a simple HQL query:

This example demonstrates a simple query to retrieve all instances of the Employee entity. The FROM clause in HQL is used similarly to SQL to specify the entity class to query from.

Selecting Specific Columns

To select specific fields of an entity, you can use the SELECT clause in HQL. Here's how you can do it:

This query selects only the firstName and lastName properties of the Employee entity. The results are returned as a list of object arrays.

Applying Conditions with WHERE Clause

Like SQL, HQL allows the use of the WHERE clause to filter records. Here’s an example:

This query retrieves all employees with a salary greater than 50,000.

Ordering Query Results

To sort the query results, you can use the ORDER BY clause. Below is an example of ordering employees by their first names:

This query orders the employees in ascending order based on their first name. You can also use DESC for descending order.

Using JOINs in HQL

HQL supports joining multiple entities, similar to SQL joins. Here is an example of how to use joins in HQL:

This query joins the Employee entity with the Department entity, selecting the employee's first name and the department name.

Conclusion

Hibernate Query Language (HQL) is a powerful tool for querying databases in a way that leverages the object-oriented nature of Java. Understanding and using HQL allows for efficient data retrieval and manipulation, enhancing the capabilities of Java applications.

Explore more Hibernate features to fully harness the power of this ORM framework in your Java applications.

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