无法从子项中获取父项数据

Question

我正在尝试查看是否将 Cab 分配给任何 Employee，以便我可以获取该 Employee Id 并将 cab 设置为 null，但是 @OneToMany 映射，只是返回一个员工列表 & 通过这个我没有得到任何方法，比如 cab.getEmp() 来获取员工详细信息

Employee.java

@Data
@Entity
@Table(name = "employee")
public class Employee {
    
     @Id
     private Integer id;
     private String username;
     private String password;
     private String role;
     private String dropLocation;
    
     @ManyToOne(
         cascade = CascadeType.ALL,
         fetch = FetchType.EAGER
     )
    
     @JoinColumn(
         name = "empCab",
         referencedColumnName = "cabId"
     )

     public Cab cab;
}

Cab.java

@Data
@Entity
@Table(name = "cab")
public class Cab {
    
     @Id
     private Integer cabId;
     private Integer cabNumber;
     private String cabShift;
        
     @OneToMany(
         cascade = CascadeType.ALL,
         fetch = FetchType.EAGER,
         mappedBy= "cab"
     )

     private List<Employee> emp = new ArrayList<>();
}

控制器

@GetMapping("deleteCab")
public ModelAndView deleteCab(@RequestParam("id") Integer id, ModelAndView mvc){
         Cab cab = cabRepo.findById(id).orElse(null);
         if(cab!=null){
             List<Employee> emp =  cab.getEmp();
             if(!cab.getEmp().isEmpty()){
                 //e1.setCab(null);
                 //empRepo.save(e1);
                 mvc.addObject("msg", "Cab deleted & an employee cab detail also got changed");
                 mvc.setViewName(NOTHING_JSP);
             } else {
                 cabRepo.deleteById(id);
                 mvc.addObject("msg", "Cab removed from the database");
                 mvc.setViewName(NOTHING_JSP);
             }
         }
}

Answer 1

在您的代码中，Cab 是永久的 class，Employee 是子 class，您的目标是移除子 class 对父的依赖class。为此，您必须从 Cab 中提取 Employee 并使用 employee.setCab(null).

删除与 Cab 的关系

@GetMapping("/deleteCab")
@ResponseBody
public ModelAndView deleteCab(@RequestParam("id") Integer id, ModelAndView mvc){
    Cab cab = cabRepo.findById(id).orElse(null);
    if(cab != null){
         // Extract employee from cab
         for(Employee emp: cab.getEmp())
         {
            // Remove the relationship with cab
            emp.setCab(null);
         }
         cabRepo.save(cab);
         mvc.addObject("msg", "Cab deleted & an employee cab detail also got changed");
         mvc.setViewName(NOTHING_JSP);
    } else {
         cabRepo.deleteById(id);
         mvc.addObject("msg", "Cab removed from the database");
         mvc.setViewName(NOTHING_JSP);
    }
    return mvc;
}

无法从子项中获取父项数据

Unable to fetch Parent data from Child

java

spring-boot

hibernate

mapping