Question

我有两个实体，关系是OneToMany / ManyToOne

教师

 @Entity
@JsonIgnoreProperties({"password"})
public class Teacher extends ResourceSupport{

        @Id
        @GeneratedValue
        private Long id;
        @OneToMany(mappedBy = "teacher")
        private List<Course> courses;

       @JsonCreator
        public Teacher(@JsonProperty("Username") String username
            ,@JsonProperty("Password") String password){

                 this.username = username;
                 this.password = password;
        }

         public List<Course> getCourses() {
              return courses;
        }

        public void setCourses(List<Course> courses) {
              this.courses = courses;
        }

        public String getUsername(){
             return username;
        }

        public String getPassword(){
             return password;
        }

        @Setter
        private String username;


        @Setter
        private String password;

       Teacher(){

        }

}

课程实体

@Entity
@NoArgsConstructor
@JsonIgnoreProperties({"teacher"})
public class Course {

    @Getter @GeneratedValue(strategy = GenerationType.AUTO) @Id private Long identifier;
    @Getter @Setter @NotNull private String name;
    @Getter @Setter @NotNull private  String description;
    @Getter @Setter @ManyToOne private Teacher teacher;

    @JsonCreator
    public Course(@JsonProperty("Name") String name , @JsonProperty("Description") String description , @JsonProperty("Teacher")Teacher teacher){
        this.description = description;
        this.name = name;
        this.teacher= teacher;
    }


}

如果我在PostRequest中通过邮递员创建2个教师对象，我会将它们带到具有特定ID的桌面上。

但是当我创建一个课程时，它会从id 1开始，它需要最后一个教师ID并从那里开始。

这就是我得到的

     [
    {
        "courses": [
            {
                "identifier": 3,
                "name": "java",
                "description": "java basico"
            }
        ],
        "username": "teuddy",
        "links": [
            {
                "rel": "self",
                "href": "http://localhost:8181/teachers/teuddy"
            }
        ]
    },
    {
        "courses": [],
        "username": "rafael",
        "links": [
            {
                "rel": "self",
                "href": "http://localhost:8181/teachers/rafael"
            }
        ]
    }
]

这个课程不是第一个，而是三分之一，为什么？

H2 DATABASE https://i.stack.imgur.com/haoUy.png

Answer 1

您在两个实体中使用@GeneratedValue（strategy = GenerationType.AUTO）和@GeneratedValue，默认为GenerationType.AUTO。这意味着确定适用于所用DB的ID生成器。如果H2数据库是全局序列。因此，所有实体都共享此序列以生成id。

还有其他策略，但H2不支持afaik IDENTITY，也会回到SEQUENCE。

如果对您来说重要的是实体不共享其ID，您可以尝试使用TABLE策略，但我不推荐这样做。（有关更多信息，请阅读Why-you-should-never-use-the-table-identifier-generator-with-jpa-and-hibernate

具有相同自动生成ID的两个表

1 个答案: