JPA：外键注释

Question

I've got two database entities: Forum and Topic .

Topic has protected long forumId data member, which indicates of course the Topic 's forum.

My question is what annotation to use for this data member?

Answer 1

As Forum has many topics, and a topic belongs to one and only Forum, you probably want to go with a Forum type attribute annotated with @ManyToOne :

@ManyToOne
@JoinColumn(name = "forumId")
private Forum forum;

See more:

ManyToOne and JPA mapping

Answer 2

As others have answered -
You should use the ManyToOne , and JoinColumn annotations.
Bare in mind , that since JPA is about ORM - Object relational mapping,
You should reference another object as you would have done "naturally" in Java - ie via an object and not via its identifier (which is forumId) in your case),
This was one of the design consideration between the relations at JPA and Hibernate (previously to JPA).

Answer 3

@ManyToOne正如注释所暗示的那样 - 每个论坛都有很多主题