Spring Data JPA规范继承

Question

我有三个实体，如下所示：

@Entity
@Inheritance(strategy = InheritanceType.JOINED)
@DiscriminatorColumn(name = "type")
public abstract class Employee {
    @Id
    protected Long id;
    ...
}

@Entity
public class FullTimeEmployee extends Employee {
    protected Integer salary;
    ...
}

@Entity
public class PartTimeEmployee extends Employee {
    protected Float hourlyWage;
}

我尝试使用Spring Data Specification查询，如下所示：

我的Spring数据托管存储库：

@Repository
public interface EmployeeRepository<T extends Employee> extends JpaRepository<T, Long> {
    Page<T> findAll(Specification<T> specification, Pageable pageable);
}

还有我的样品控制器

@Controller
public class MyController {
    private final EmployeeRepository employeeRepository;

    @Autowired
    public MyController(EmployeeRepository employeeRepository) {
        this.employeeRepository = employeeRepository;
    }

    @GetMapping("/")
    public ModelAndView queryEmployeeExample(EmployeeQueryDTO query) {
        Page response = this.employeeRepository.findAll((root, criteriaQuery, criteriaBuilder) -> {
            ArrayList<Predicate> predicates = new ArrayList<>();
            if(query.getId() != null) {
                predicates.add(
                    criteriaBuilder.equal(root.get("id"), query.getId())
                );
            }
            if(query.getSalary() != null) {
                predicates.add(
                    criteriaBuilder.equal(root.get("salary"), query.getSalary())
                );
            }
            if(query.getHourlyWage() != null) {
                predicates.add(
                    criteriaBuilder.equal(root.get("hourlyWage"), query.getHourlyWage())
                );
            }
            return criteriaBuilder.and(predicates.toArray(new Predicate[predicates.size()]));
        }, new PageRequest(0, 100));

        return new ModelAndView("index")
                    .addObject("result", response);
    }

    @Getter
    @Setter
    static class EmployeeQueryDTO {
        private Long id;
        private Integer salary;
        private Float hourlyWage;
    }
}

我可以使用id执行查询，但是其他参数（例如salary和hourlyWage）不会发生相同的情况，我收到此异常：

java.lang.IllegalArgumentException：无法在此ManagedType [Employee]上找到具有给定名称[salary / hourlyWage]的Attribute

我了解问题是要在超类中查找该字段，并且该字段不存在，我想知道是否可以解决我的问题？

问候。

Answer 1

作为@JBNizet使用“ CriteriaBuilder.treat（）”的技巧：

@GetMapping("/")
public ModelAndView queryEmployeeExample(EmployeeQueryDTO query) {
    Page response = this.employeeRepository.findAll((root, 
                                                    criteriaQuery, 
                                                    criteriaBuilder) -> {

    ArrayList<Predicate> predicates = new ArrayList<>();

    if(query.getId() != null) {
        predicates.add(
            criteriaBuilder.equal(
                    root.get("id"), 
                    query.getId()
            )
        );
    }
    if(query.getSalary() != null) {
        //Downcast Root object to the specified type.
        Root<FullTimeEmployee> rootFullTImeEmployee = criteriaBuilder
                                        .treat(root, FullTimeEmployee.class);
        predicates.add(
            criteriaBuilder.equal(
                    rootFullTImeEmployee.get("salary"), 
                    query.getSalary()
            )
        );
    }
    if(query.getHourlyWage() != null) {
        //Downcast Root object to the specified type.
        Root<PartTimeEmployee> rootPartTimeEmployee = criteriaBuilder
                                        .treat(root, PartTimeEmployee.class);
        predicates.add(
            criteriaBuilder.equal(
                    rootPartTimeEmployee.get("hourlyWage"), 
                    query.getHourlyWage()
            )
        );
    }
    return criteriaBuilder.and(predicates.toArray(new Predicate[predicates.size()]));}, 
                new PageRequest(0, 100));

    return new ModelAndView("index")
                .addObject("result", response);
}

@Getter
@Setter
static class EmployeeQueryDTO {
    private Long id;
    private Integer salary;
    private Float hourlyWage;
}