新表中的JPA ManyToOne [英] JPA ManyToOne in a new table

问题描述

我有下表: 标记，员工，位置. 员工和位置可以具有更多标签.我认为最好为这些关系创建新表:employee_tag和location_tag.

I have got the following tables: Tag, Employee, Location. Employee and Location can have more tags. I think it's best to create new tables for these relations so: employee_tag and location_tag.

如何使用JPA做到这一点?现在我明白了: 员工类别:

How do I do this using JPA? Right now I got this: Employee class:

@OneToMany()
@JoinTable(name="employee_tag", joinColumns={
    @JoinColumn(name="ID_employee", referencedColumnName="ID")
}, inverseJoinColumns={
    @JoinColumn(name="ID_tag", referencedColumnName="ID")
})
private Collection<Tag> tags;

标记类:

@ManyToOne()
private Employee employee;

它将创建一个名为employee_tag的新表，但tag仍具有一列employee_ID.如何将标签链接到该表?

It creates a new table named employee_tag but tag still has a column employee_ID. How do I link the tag to this table?

推荐答案

如果您需要单向一对多关联，则不必将雇员关联放在标记类中，而必须在员工班.

If you need a unidirectional one-to-many association, you have not to put the employee association in the tag class, you have to declare the association in the Employee class.

@Entity
public class Employee {
   @OneToMany()
   @JoinTable(name="employee_tag", joinColumns={
   @JoinColumn(name="ID_employee", referencedColumnName="ID")
   }, inverseJoinColumns={
   @JoinColumn(name="ID_tag", referencedColumnName="ID")
   })
   public Collection<Tag> tags;
   ...
}

@Entity
public class Tag {      
   ...
}

否则，您可以如下进行双向关联:

Otherwise you can do bidirectional association as below:

@Entity
public class Employee {
   @OneToMany(mappedBy="troop")
   public Collection<Tag> tags;
   ...
}

@Entity
public class Tag {
   @ManyToOne
   @JoinColumn(name="employee_fk")
   public Employee employee;
   ...
}

看看休眠注释文档

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