java如何从关系中仅检索属性而不是实体?
我在Netbeans中从事一个maven web应用程序项目,我有以下课程:
@Entity
@Table(name = "departments")
public class Department{
@Id
private Integer departmentId;
@Column(name = "department_name")
private String departmentName;
}
以及:
@Entity
@Table(name = "employees")
public class Employee {
@Id
private Integer employeetId;
@Column(name = "employee_name")
private String employeeName;
@JoinColumn(name = "department_id", referencedColumnName =
"department_id")
@ManyToOne(optional = false)
private Departments department;
}
我的rest api返回以下内容:
{
employeeId:1,
employeeName:"Jhon",
department: { departmentId:1, departmentName:"IT"}
}
我期望的输出是:
{
employeeId:1,
employeeName:"Jhon",
department: "IT"
}
我尝试返回DTO,但得到的是空json:
@GET
@Produces(MediaType.APPLICATION_JSON)
public List<EmployeeDto> findAllEmployees() {
CriteriaQuery cq = entityManager.getCriteriaBuilder().createQuery(Employee.class);
cq.select(cq.from(Employee.class));
List<Employee> employees = entityManager.createQuery(cq).getResultList();
List<EmployeeDto> employeesDto = new ArrayList<>();
for (Employee employee : employees) {
EmployeeDto employeeDto = new EmployeeDto();
employeeDto.employeeId = employee.getEmployeedId();
employeeDto.department = employee.getDepartment().getDepartmentName();
employeesDto.add(employeeDto);
}
return employeesDto;
DTO:
Class EmployeeDto{Integer employeeId; String employeeName; String department}
# 1 楼答案
这是因为我得到了一个空的json:我的Dto类没有公共的getter和setter。 解决方案是将Dto字段公开或添加公共getter/setter
# 2 楼答案
使用namedquery
您可以找到有关NamedQuery的更多信息:
https://www.petrikainulainen.net/programming/spring-framework/spring-data-jpa-tutorial-creating-database-queries-with-named-queries/