如何在具有多个表的休眠状态下呈现树结构? [英] How to render a tree structure in hibernate with multiple tables?

问题描述

我需要从其中定义了两个表的数据库中检索树:

I need to retrieve a tree from a DB in which I have two tables defined:

• 节点在这里，我定义了一个节点元素

• node Here I define a node element

关系在这里，我通过指定使用ID的父母和孩子来定义树结构

relation Here I define the tree structure by specifying parents and children making use of IDs

在Internet上，我只找到带有单个表(即节点1)的表的示例，其中定义了节点和关系:

Looking on the Internet I only find examples with a single table, the node one, in which both nodes and relations are defined:

@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>();

}

即使它更简单，我也不喜欢它，因为基础表没有被规范化.

Even though it is simpler I don't like it very much because the underlying tables are not normalized.

任何人都可以使用两个表为我提供一个简单的示例吗?

Anyone can provide me with a simple example using two tables?

推荐答案

您可能希望在关系"表中有两列，

You may want to have two columns in Relationship table,

| id | parent_id |

|id | parent_id|

父节点条目将针对该节点的ID更新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;

类似地，子节点将根据ID的parent_id更新ID. 节点

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;

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