为什么Hibernate尝试插入具有ID的新记录？

Question

Why Hibernate tries to insert new record with existing id?

Category table before save (was filled manually with insert)

ID | NAME  | IMAGE
1  | 'NAME'| 'IMAGE'

Save code

//Category{id=0, name='NAME', image='IMAGE', parent=null}
getCurrentSession().save(category);

Should be inserted with id 2.

Category Java code

@Entity
@Table(name = "CATEGORY",
    indexes = {
            @Index(name = "CATEGORY_NAME_INDEX",
                    columnList = "CATEGORY_NAME")})
public class Category implements NamedModel {
    @Id
    @Column(name = "CATEGORY_ID")
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;
    @NotNull
    @Size(min = 1, max = 256)
    @Column(name = "CATEGORY_NAME", length = 256)
    private String name;
    @OneToOne(fetch = FetchType.EAGER)
    @JoinTable(name = "CATEGORY_RELATIONS",
            joinColumns = {
                    @JoinColumn(name = "CATEGORY_RELATIONS_CATEGORY_ID", 
                                referencedColumnName = "CATEGORY_ID")},
            inverseJoinColumns = {
                    @JoinColumn(name = "CATEGORY_RELATIONS_PARENT_ID",
                                referencedColumnName = "CATEGORY_ID")})
private Category parent;
    @OneToMany(cascade = {CascadeType.REMOVE, CascadeType.PERSIST}, 
               fetch = FetchType.LAZY, mappedBy = "parent")
    private List<Category> children;
}

SOLUTION

//Category
@GeneratedValue(strategy = GenerationType.IDENTITY) 

//CategoryRelations
@Entity
@IdClass(CategoryRelationsPrimaryKey.class)
public static class CategoryRelationsPrimaryKey implements Serializable {
    private Long categoryId;
    private Long parentId; 

instead of long.

Answer 1

This is because you had deleted/added a record from database directly instead from the application ie ORM, that's why values in hibernate_sequence is no longer maintained.

Hibernate maintains values in a hibernate_sequence table which would be inserted on creating a new record.

update next_val column value in hibernate_sequence to resolve the problem.

You can use Annotation @GeneratedValue(strategy = GenerationType.IDENTITY) to delegate primary key generation to database.