当我在存储库中保存对象时，为什么相同的 id 会增加？答案

【问题标题】：Why the same id is incremented when I save an object in the repository?当我在存储库中保存对象时，为什么相同的 id 会增加？
【发布时间】：2016-08-11 15:08:22
【问题描述】：

每当我调用 save() 方法时，相同的 ID 在三个不同的实体之间共享，我不知道为什么？

@Entity
public class Department {
    @Id
    @GeneratedValue
    private Long departmentId;
    private String name;

    public Department(Long departmentId) {
        this.departmentId = departmentId;
    }

    public Department() {
    }

    public Department(String name) {
        this.name = name;
    }

    public Long getDepartmentId() {
        return departmentId;
    }

    public void setDepartmentId(Long departmentId) {
        this.departmentId = departmentId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

@Entity
public class Location {
    @Id
    @GeneratedValue
    private Long locationId;
    private String name;

    public Location(Long locationId) {
        this.locationId = locationId;
    }

    public Location() {
    }

    public Location(String name) {
        this.name = name;
    }

    public Long getLocationId() {
        return locationId;
    }

    public void setLocationId(Long locationId) {
        this.locationId = locationId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

这是我的控制器：

@RestController
public class SettingsController {

    @Autowired
    private LocationRepository locationRepository;
    @Autowired
    private DepartmentRepository departmentRepository;
    @Autowired
    private RoleRepository roleRepository;

    @RequestMapping(value = "/api/locations", method = RequestMethod.POST)
    public ResponseEntity addLocation(@RequestBody DataForm dataForm) {
        if (dataForm == null) {
            return new ResponseEntity(HttpStatus.BAD_REQUEST);
        }
        locationRepository.save(new Location(dataForm.getName()));
        return new ResponseEntity(HttpStatus.CREATED);
    }

    @RequestMapping(value = "/api/roles", method = RequestMethod.POST)
    public ResponseEntity addRole(@RequestBody DataForm dataForm) {
        if (dataForm == null) {
            return new ResponseEntity(HttpStatus.BAD_REQUEST);
        }
        roleRepository.save(new Role(dataForm.getName()));
        return new ResponseEntity(HttpStatus.CREATED);
    }

    @RequestMapping(value = "/api/departments", method = RequestMethod.POST)
    public ResponseEntity addDepartment(@RequestBody DataForm dataForm) {
        if (dataForm == null) {
            return new ResponseEntity(HttpStatus.BAD_REQUEST);
        }
        departmentRepository.save(new Department(dataForm.getName()));
        return new ResponseEntity(HttpStatus.CREATED);
    }
}

只有当 id 是静态的时才会发生这种情况，但事实并非如此。如果我创建两个新的 Location() 对象，当我创建一个新的 Department() 时，部门的 ID 将为 3。为什么？

【问题讨论】：

标签： java spring hibernate api rest

【解决方案1】：

由于您没有为@GeneratedValue 指定策略，我猜Hibernate 对您的所有实体使用相同的序列。

你可以设置类似

@Id
@GeneratedValue(strategy=GenerationType.SEQUENCE, generator="department_seq_gen")
@SequenceGenerator(name="department_seq_gen", sequenceName="DEPARTMENT_SEQ")

在Department 实体上，以及在Location 实体上的类似内容（只需使用location_seq_gen 和LOCATION_SEQ）。

【讨论】：