Spring supports the usage of restricted SpEL template expressions in manually defined queries that are defined with @Query.
In this tutorial, we will see the usage of variable entityName. It is used in query as shown in following example:
@Query("SELECT e FROM #{#entityName} e WHERE .... ")
The one of the advantages of the above as compared to the hard-coded entity name is, entityName is resolved dynamically. As JPQL looks for the entity name either by looking at @Entity#name attribute (if that exists as specified in say, @Entity(name = "Emp")), or entity simple class name. That means from refactoring perspective (i.e. if we need to change the entity name via @Entity#name ) then we don't have to update it manually every time in the query declared by @Query.
Example
Entity
@Entity(name = "emp")
public class Employee {
private @Id
@GeneratedValue
Long id;
private String name;
private String dept;
private int salary;
.............
}
Repository interface
package com.logicbig.example;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.CrudRepository;
import java.util.List;
public interface EmployeeRepository extends CrudRepository<Employee, Long> {
@Query("SELECT e FROM #{#entityName} e WHERE e.dept = ?1")
public List<Employee> findByDepartment(String deptName);
}
Example Client
@Component
public class ExampleClient {
@Autowired
private EmployeeRepository repo;
public void run() {
List<Employee> employees = createEmployees();
repo.saveAll(employees);
System.out.println(" -- finding all employees --");
Iterable<Employee> all = repo.findAll();
all.forEach(System.out::println);
System.out.println(" -- finding by dept Admin --");
List<Employee> list = repo.findByDepartment("Admin");
list.forEach(System.out::println);
}
private List<Employee> createEmployees() {
return Arrays.asList(
Employee.create("Diana", "Admin", 2000),
Employee.create("Mike", "Sale", 1000),
Employee.create("Rose", "IT", 4000),
Employee.create("Sara", "Admin", 3500),
Employee.create("Randy", "Sale", 3000),
Employee.create("Charlie", "IT", 2500)
);
}
}
Main class
public class ExampleMain {
public static void main(String[] args) {
AnnotationConfigApplicationContext context =
new AnnotationConfigApplicationContext(AppConfig.class);
ExampleClient exampleClient = context.getBean(ExampleClient.class);
exampleClient.run();
EntityManagerFactory emf = context.getBean(EntityManagerFactory.class);
emf.close();
}
} -- finding all employees -- Employee{id=1, name='Diana', dept='Admin', salary=2000} Employee{id=2, name='Mike', dept='Sale', salary=1000} Employee{id=3, name='Rose', dept='IT', salary=4000} Employee{id=4, name='Sara', dept='Admin', salary=3500} Employee{id=5, name='Randy', dept='Sale', salary=3000} Employee{id=6, name='Charlie', dept='IT', salary=2500} -- finding by dept Admin -- Employee{id=1, name='Diana', dept='Admin', salary=2000} Employee{id=4, name='Sara', dept='Admin', salary=3500}
Example ProjectDependencies and Technologies Used: - spring-data-jpa 2.0.7.RELEASE: Spring Data module for JPA repositories.
Uses org.springframework:spring-context version 5.0.6.RELEASE - hibernate-core 5.3.1.Final: Hibernate's core ORM functionality.
Implements javax.persistence:javax.persistence-api version 2.2 - h2 1.4.197: H2 Database Engine.
- JDK 1.8
- Maven 3.3.9
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