Following example shows how to use interface based nested Projections.
Example
Entities
@Entity
public class Employee {
@Id
@GeneratedValue
private Integer id;
private String name;
@ManyToOne(cascade = CascadeType.ALL)
private Department department;
private int salary;
.............
}
@Entity
public class Department {
@Id
@GeneratedValue
private Integer id;
private String deptName;
private String location;
.............
}
Defining Projections
public interface EmployeeInfo {
String getName();
int getSalary();
DeptInfo getDepartment();
interface DeptInfo {
String getDeptName();
}
}
In above class, EmployeeInfo is the main projection to get the selected attributes and DeptInfo is the nested projection to get department name only.
Creating Repository
public interface EmployeeRepository extends CrudRepository<Employee, Long> {
List<EmployeeInfo> findBy();
List<EmployeeInfo> findBySalaryBetween(int salaryMin, int salaryMax);
List<EmployeeInfo> findByDepartmentLocation(String location);
}
The third query method in above example is nested derived query method which applies condition equivalent to JPQL 'where employee.department.location = ?'.
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(" -- All EmployeeInfo --");
List<EmployeeInfo> list = repo.findBy();
for (EmployeeInfo ei : list) {
EmployeeInfo.DeptInfo di = ei.getDepartment();
System.out.printf("Name: %s, Salary: %s, Dept: %s%n",
ei.getName(), ei.getSalary(), di.getDeptName());
}
System.out.println(" -- EmployeeInfo with salary between 3000 and 4000 --");
list = repo.findBySalaryBetween(3000, 4000);
for (EmployeeInfo ei : list) {
EmployeeInfo.DeptInfo di = ei.getDepartment();
System.out.printf("Name: %s, Salary: %s, Dept: %s%n",
ei.getName(), ei.getSalary(), di.getDeptName());
}
System.out.println(" -- EmployeeInfo with dept Location TX --");
list = repo.findByDepartmentLocation("TX");
for (EmployeeInfo ei : list) {
EmployeeInfo.DeptInfo di = ei.getDepartment();
System.out.printf("Name: %s, Salary: %s, Dept: %s%n",
ei.getName(), ei.getSalary(), di.getDeptName());
}
}
private List<Employee> createEmployees() {
return Arrays.asList(
Employee.of("Diana", Department.of("Admin", "NY"), 3000),
Employee.of("Mike", Department.of("IT", "TX"), 35000),
Employee.of("Rose", Department.of("Sales", "NC"), 4000),
Employee.of("Sara", Department.of("Admin", "TX"), 3500),
Employee.of("Joe", Department.of("IT", "TX"), 3000),
Employee.of("Charlie", Department.of("IT", "NY"), 4500)
);
}
}
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', department=Department{id=2, deptName='Admin', location='NY'}} Employee{id=3, name='Mike', department=Department{id=4, deptName='IT', location='TX'}} Employee{id=5, name='Rose', department=Department{id=6, deptName='Sales', location='NC'}} Employee{id=7, name='Sara', department=Department{id=8, deptName='Admin', location='TX'}} Employee{id=9, name='Joe', department=Department{id=10, deptName='IT', location='TX'}} Employee{id=11, name='Charlie', department=Department{id=12, deptName='IT', location='NY'}} -- All EmployeeInfo -- Name: Diana, Salary: 3000, Dept: Admin Name: Mike, Salary: 35000, Dept: IT Name: Rose, Salary: 4000, Dept: Sales Name: Sara, Salary: 3500, Dept: Admin Name: Joe, Salary: 3000, Dept: IT Name: Charlie, Salary: 4500, Dept: IT -- EmployeeInfo with salary between 3000 and 4000 -- Name: Diana, Salary: 3000, Dept: Admin Name: Rose, Salary: 4000, Dept: Sales Name: Sara, Salary: 3500, Dept: Admin Name: Joe, Salary: 3000, Dept: IT -- EmployeeInfo with dept Location TX -- Name: Mike, Salary: 35000, Dept: IT Name: Sara, Salary: 3500, Dept: Admin Name: Joe, Salary: 3000, Dept: IT
Example ProjectDependencies and Technologies Used: - spring-data-jpa 2.0.9.RELEASE: Spring Data module for JPA repositories.
Uses org.springframework:spring-context version 5.0.8.RELEASE - hibernate-core 5.3.5.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 3.5.4
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