java 休眠同表父/子关系
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Hibernate same table parent / child relation
提问by antohoho
I have Parent/Child relationship in a single-table, let's say as simple as
我在单表中有父/子关系，让我们说简单
id | parent_id | some_data
I am trying to understand / implement best practices how to build Hibernate classes for single table relationship.
我正在尝试了解/实现如何为单表关系构建 Hibernate 类的最佳实践。
I have a feed that comes from somewhere and it has nested JSON structure, so after parse it I want to have it representation in OracleDB.
我有一个来自某个地方的提要，它有嵌套的 JSON 结构，所以在解析它之后我想在 OracleDB 中让它表示。
Feed looks like
饲料看起来像
{
1:
=> 2:
=> 3
=> 4:
=> 5
=> 6
}
this data should end up in db as :
此数据应以 db 结尾：
1 | 0 (main rec, no parent)
2 | 1
3 | 2
4 | 2
5 | 4
6 | 1
And it could go deeper and deeper...
它可能会越来越深......
I would like to traverse JSON structure and build classes that at the end I save in db
我想遍历 JSON 结构并构建最后保存在 db 中的类
session.save(parent)
parent would be instance of my hibernate mapped class, lets name it Feed.
parent 将是我的休眠映射类的实例，我们将其命名为 Feed。
Each time I descend a tree, it creates a new Feed, finds it's parent and add it to the list.
每次我下树时，它都会创建一个新的 Feed，找到它的父级并将其添加到列表中。
Feed **parent** = new Feed();
-> Feed child2 = new Feed();
child2.setParent(parent)
parent.add(child2);
-> Feed child3 = new Feed();
child3.setParent(child2)
child2.add(child3);
Feed child4 = new Feed();
child4.setParent(child2)
child2.add(child4);
.............
session.save(**parent**)
My question is could I use @ManyToOne and @OneToMany approach?
我的问题是我可以使用 @ManyToOne 和 @OneToMany 方法吗？
I also looked at @Inheritance(strategy = InheritanceType.SINGLE_TABLE) but I do not think I could apply it to my problem since I do not know parents, they are dynamic. I could not build parent class and extend it.
我还查看了 @Inheritance(strategy = InheritanceType.SINGLE_TABLE) 但我不认为我可以将它应用于我的问题，因为我不认识父母，他们是动态的。我无法构建父类并扩展它。
So bottom line I am trying to solve two problems
所以底线我试图解决两个问题
Easy save on a parent level
How to get data from a parent to a leaf when I need it
轻松保存在父级
如何在需要时从父级获取数据到叶子
Some Hibernate Mapped Classes example would be very appreciated.
一些 Hibernate Mapped Classes 示例将不胜感激。
回答by antohoho
Seems like all I needed to do is:
似乎我需要做的就是：
@Entity
@Table(name = "table_name")
public class TableName{
......
@Transient
private Long parentId;
......
@ManyToOne(fetch = FetchType.LAZY, optional=true)
@JoinColumn(name="parent_id")
private TableName parent;
@OneToMany(mappedBy="parent", fetch = FetchType.LAZY, cascade = CascadeType.ALL, orphanRemoval=true)
private Set<TableName> children = new HashSet<TableName>();
Than simply
比简单的
TableName papa = new TableName();
papa.setParent(null); // parent
TableName kid1 = new TableName();
kid1.setParent(papa);
papa.getChildren().add(kid1);
TableName kid1_1 = new TableName();
kid1_1.setParent(kid1);
kid1.getChildren().add(kid1_1);
TableName kid2 = new TableName();
kid2.setParent(papa);
papa.getChildren().add(kid2);
session.save(papa)
回答by anirban
Why don't you create a self referencing one to many relation keeping cascade = all. So individual child objects need not be saved separately. Only saving parent is enough. For example.
为什么不创建一个自引用的一对多关系保持级联 = 全部。因此不需要单独保存单个子对象。只有保存父母就足够了。例如。
Adding a one to many relationship to a self reference parent/child
