Question

我不明白，Hibernate是否应该自动工作？

我有Category实体，编码如下：

@Entity
public class Category {

@Id
public String Url;

@OneToMany
@JoinTable(name = "category_childs")
private Set<Category> childs = new HashSet<Category>();

@OneToMany
@JoinTable(name = "category_parents")
private Set<Category> parents = new HashSet<Category>();

@OneToMany(cascade=CascadeType.ALL)
private Set<Person> persons = new HashSet<Person>();

public String Title;

public boolean Done;

这会导致创建下表

CREATE TABLE
category_parents
(
    Category_Url VARCHAR(255) NOT NULL,
    parents_Url VARCHAR(255) NOT NULL,
    PRIMARY KEY (Category_Url, parents_Url),
    CONSTRAINT FK9BB292C83275D6D7 FOREIGN KEY (Category_Url) REFERENCES category (Url) ,
    CONSTRAINT FK9BB292C8569C2962 FOREIGN KEY (parents_Url) REFERENCES category (Url),
    CONSTRAINT parents_Url UNIQUE (parents_Url),

这是不正确的，因为parents_Url不应该是唯一的（应允许多行具有相同的父级）。

如果我没有@JoinTable规范进行编码

@Entity
public class Category {

@Id
public String Url;

@ManyToMany(cascade=CascadeType.ALL)
//@JoinTable(name = "category_childs")
private Set<Category> childs = new HashSet<Category>();

@ManyToMany(cascade=CascadeType.ALL)
//@JoinTable(name = "category_parents")
private Set<Category> parents = new HashSet<Category>();

@OneToMany(cascade=CascadeType.ALL)
private Set<Person> persons = new HashSet<Person>();

public String Title;

public boolean Done;

然后我会有以下

CREATE TABLE
category_category
(
    Category_Url VARCHAR(255) NOT NULL,
    parents_Url VARCHAR(255) NOT NULL,
    childs_Url VARCHAR(255) NOT NULL,
    PRIMARY KEY (Category_Url, childs_Url),
    CONSTRAINT FK8635931F3275D6D7 FOREIGN KEY (Category_Url) REFERENCES category (Url) ,
    CONSTRAINT FK8635931F569C2962 FOREIGN KEY (parents_Url) REFERENCES category (Url) ,
    CONSTRAINT FK8635931F6ADF3430 FOREIGN KEY (childs_Url) REFERENCES category (Url),

如何让Hibernate创建具有两个字段的关系表？

如下：

CREATE TABLE
category_category
(
    parents_Url VARCHAR(255) NOT NULL,
    childs_Url VARCHAR(255) NOT NULL,
    PRIMARY KEY (parents_Url, childs_Url),
    CONSTRAINT FK8635931F569C2962 FOREIGN KEY (parents_Url) REFERENCES category (Url) ,
    CONSTRAINT FK8635931F6ADF3430 FOREIGN KEY (childs_Url) REFERENCES category (Url),

Answer 1

Hibernate在第一种情况下创建了一个唯一的列，因为你正在使用@OneToMany告诉hibernate一个类别最多只有一个父类。在您注释掉@JoinTable的代码中，您还将@OneToMany更改为@ManyToMany。这就是hibernate在这种情况下不会创建唯一约束的原因。

我认为该类别的孩子将该类别本身作为父母。在这种情况下，必须使用mappedBy中的@ManyToMany将孩子或父母定义为关系的另一面：

@ManyToMany
@JoinTable(name = "category_childs")
private Set<Category> childs = new HashSet<Category>();

@ManyToMany(mappedBy="childs")
private Set<Category> parents = new HashSet<Category>();

如何正确实现@ManyToMany映射？

1 个答案: