In Spring Data JPA, projects can also be specified during runtime by using generic repository methods. For example:
public interface EmployeeRepository extends CrudRepository<Employee, Long> {
<T> List<T> findByDept(String dept, Class<T> type);
}
Example
Entity
@Entity
public class Employee{
private @Id
@GeneratedValue
Long id;
private String name;
private String dept;
private int salary;
private String phone;
.............
}
Repository
public interface EmployeeRepository extends CrudRepository<Employee, Long> {
<T> List<T> findByDept(String dept, Class<T> type);
}
Projection classes
public class SalaryInfo {
private String name;
private int salary;
public SalaryInfo(String name, int salary) {
this.name = name;
this.salary = salary;
}
.............
}
public class ContactInfo {
private String name;
private String phone;
public ContactInfo(String name, String phone) {
this.name = name;
this.phone = phone;
}
.............
}
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 SalaryInfo for IT dept --");
List<SalaryInfo> list = repo.findByDept("IT", SalaryInfo.class);
list.forEach(System.out::println);
System.out.println(" -- finding ContactInfo for IT dept --");
List<ContactInfo> list2 = repo.findByDept("IT", ContactInfo.class);
list2.forEach(System.out::println);
}
private List<Employee> createEmployees() {
return Arrays.asList(
Employee.create("Diana", "Admin", 3000, "111-111-111"),
Employee.create("Mike", "IT", 1000, "222-222-222"),
Employee.create("Rose", "Admin", 4000, "333-333-333"),
Employee.create("Sara", "Admin", 3500, "444-444-444"),
Employee.create("Tanaka", "IT", 3000, "555-555-555"),
Employee.create("Charlie", "IT", 450, "666-666-666")
);
}
}
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=3000} Employee{id=2, name='Mike', dept='IT', salary=1000} Employee{id=3, name='Rose', dept='Admin', salary=4000} Employee{id=4, name='Sara', dept='Admin', salary=3500} Employee{id=5, name='Tanaka', dept='IT', salary=3000} Employee{id=6, name='Charlie', dept='IT', salary=450} -- finding SalaryInfo for IT dept -- SalaryInfo{name='Mike', salary=1000} SalaryInfo{name='Tanaka', salary=3000} SalaryInfo{name='Charlie', salary=450} -- finding ContactInfo for IT dept -- ContactInfo{name='Mike', phone='222-222-222'} ContactInfo{name='Tanaka', phone='555-555-555'} ContactInfo{name='Charlie', phone='666-666-666'}
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 5.3.6.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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