java - 如何在 hibernate 中渲染具有多个表的树结构？

Question

我需要从数据库中检索一棵树，其中定义了两个表:

• node这里我定义了一个节点元素

• 关系这里我通过使用ID指定父级和子级来定义树结构

在互联网上查找，我只找到具有单个表(节点表)的示例，其中定义了节点和关系:

@Entity 
@Table(name = "tree")
public class Node { 

    @Id 
    @GeneratedValue
    private Integer id; 

    @NotNull 
    private String name; 

    @OneToMany 
    @JoinColumn(name = "parent_id") 
    @OrderColumn 
    private List<Node> children = new LinkedList<Node>();

}

尽管它更简单，但我不太喜欢它，因为基础表没有标准化。

任何人都可以为我提供一个使用两个表的简单示例吗？

Answer 1

您可能希望在关系表中有两列，

|id | parent_id|

Parent Node entry will update the parent_id against the id of the node

    @ManyToOne(fetch = FetchType.EAGER, cascade=CascadeType.ALL)
@JoinTable(name="Relationship", joinColumns =  @JoinTable(name = "Relationship", joinColumns = @JoinColumn(name = "parent_id", referencedColumnName = "id"), inverseJoinColumns = @JoinColumn(name = "id", referencedColumnName = "id"))@Fetch(FetchMode.SELECT)
 private Node parentNode;

Similarly child node will update the id against the parent_id of the node

@OneToMany(fetch=FetchType.EAGER, cascade=CascadeType.ALL)
@JoinTable(name = "Relationship", joinColumns = @JoinColumn(name = "id", referencedColumnName = "id"), inverseJoinColumns = @JoinColumn(name = "parent_id", referencedColumnName = "id"))
@Fetch(FetchMode.SELECT)
 private Set<Node> childNodes;