Spring Data JPA - Interface-based Projections
Table of contents
Open Table of contents
Interface-based Projections
1. Entity
@Entity
public class Employee{
private @Id
@GeneratedValue
Long id;
private String name;
private String dept;
private int salary;
.............
}
2. Projection Interface
public interface EmployeeSalary {
String getName();
int getSalary();
}
3. Repository
public interface EmployeeRepository extends CrudRepository<Employee, Long> {
List<EmployeeSalary> findBy();
List<EmployeeSalary> findByDept(String dept);
}
Interface Based Nested Projections
1. 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;
.............
}
2. Defining Projections
public interface EmployeeInfo {
String getName();
int getSalary();
DeptInfo getDepartment();
interface DeptInfo {
String getDeptName();
}
}
3. Repository
public interface EmployeeRepository extends CrudRepository<Employee, Long> {
List<EmployeeInfo> findBy();
List<EmployeeInfo> findBySalaryBetween(int salaryMin, int salaryMax);
List<EmployeeInfo> findByDepartmentLocation(String location);
}
Open Projections
1. 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;
.............
}
2. Open Projection interface
public interface EmployeeInfo {
@Value("#{target.name+' ('+ target.department.deptName+' dept)'}")
String getDisplayString();
@Value("#{args[0]+': '+target.name+', '+args[1]+': '+ "
+ "target.department.deptName+', '+target.department.location}")
String getDetailedString(String labelName, String labelDept);
}
3. Repository
public interface EmployeeRepository extends CrudRepository<Employee, Long> {
List<EmployeeInfo> findBy();
}
Projections Using Default Methods
1. 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;
.............
}
2. Projection interface using default method
public interface EmployeeInfo {
String getName();
Department getDepartment();
default String getDisplayString() {
return String.format("Name: %s, Dept: %s", getName(),
getDepartment().getDeptName());
}
}
3.Repository
public interface EmployeeRepository extends CrudRepository<Employee, Long> {
List<EmployeeInfo> findBy();
}
Invoking Bean Methods from Projections’ SpEL expressions
1. 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;
.............
}
2. The Bean
@Component
public class EmployeeInfoBean {
public String getDisplayString(Employee employee) {
return String.format("%s (%s)", employee.getName(), employee.getDepartment().getDeptName());
}
public String getDetailedString(Employee employee, String labelName, String labelDept) {
return String.format("%s: %s, %s: %s, %s",
labelName, employee.getName(),
labelDept, employee.getDepartment().getDeptName(),
employee.getDepartment().getLocation());
}
}
3. Projection interface
public interface EmployeeInfo {
@Value("#{@employeeInfoBean.getDisplayString(target)}")
String getDisplayString();
@Value("#{@employeeInfoBean.getDetailedString(target, args[0], args[1])}")
String getDetailedString(String labelName, String labelDept);
}
Class Based Projections
1. Entity
@Entity
public class Employee{
private @Id
@GeneratedValue
Long id;
private String name;
private String dept;
private int salary;
.............
}
2. Defining class-based projection
public class EmployeeInfo {
private String name;
private int salary;
public EmployeeInfo(String name, int salary) {
this.name = name;
this.salary = salary;
}
.............
}
3. Repository
public interface EmployeeRepository extends CrudRepository<Employee, Long> {
List<EmployeeInfo> findBy();
List<EmployeeInfo> findByDept(String dept);
}
Dynamic Projections
1. Entity
@Entity
public class Employee{
private @Id
@GeneratedValue
Long id;
private String name;
private String dept;
private int salary;
private String phone;
.............
}
2. Repository
public interface EmployeeRepository extends CrudRepository<Employee, Long> {
<T> List<T> findByDept(String dept, Class<T> type);
}
3. 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;
}
.............
}
4. 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")
);
}
}
