How to use @Query annotation for custom query in Hibernate?

How to use @Query annotation for custom query in Hibernate? Hibernate's @Query annotation allows us to perform custom queries using JPQL or SQL. JPQL query: Add @Query annotation on entity class methods. Specify the JPQL query string. SQL queries: Use the @NamedNativeQuery annotation to define named native queries. Specify the query statement and result class. Practical example: We can find employees in a specific department using the following query: @Query("SELECT e FROM Employee e WHERE e.department = :department") Lista7c15504e26c2dc9d33fa17ec3230b5f findEmployeesInDepartment(@Param("department") String department);

How to use the @Query annotation in Hibernate for custom query

Introduction

Hibernate's@Query annotation allows us to define custom JPQL or SQL queries on entity classes. It provides a convenient way to perform more advanced queries without writing low-level SQL code.

JPQL Query

To use JPQL (Java Persistence Query Language), you need to add the @Query annotation to the entity class method and specify the JPQL query string. For example:

@Query("SELECT e FROM Employee e WHERE e.salary > 50000")
List<Employee> findEmployeesWithSalaryGreaterThan50000();

This code defines a query that returns all employees with a salary greater than 50,000.

SQL query

To use native SQL query, you can use the @NamedNativeQuery annotation. @NamedNativeQueries Allows us to define multiple named native queries. For example:

@NamedNativeQueries({
    @NamedNativeQuery(
        name = "findEmployeesWithSalaryGreaterThan50000",
        query = "SELECT * FROM Employee WHERE salary > 50000",
        resultClass = Employee.class
    )
})

This code defines a native SQL query called "findEmployeesWithSalaryGreaterThan50000", which returns all employees whose salary is greater than 50,000.

Practical case

Consider such an entity class:

@Entity
public class Employee {
    @Id
    private Long id;
    private String name;
    private double salary;
    //省略 getter 和 setter
}

We can use the @Query annotation to find all employees in a specific department:

@Query("SELECT e FROM Employee e WHERE e.department = :department")
List<Employee> findEmployeesInDepartment(@Param("department") String department);

Now, we can use the findEmployeesInDepartment method to get all the employees in a specific department as follows:

List<Employee> employees = employeeRepository.findEmployeesInDepartment("Engineering");

Conclusion

@Query Annotations are a powerful tool in Hibernate that allow us to execute custom queries. We can write queries using JPQL or native SQL and use named parameters to pass query parameters dynamically.

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