When Should I Use @JoinColumn or @JoinTable with JPA?

Question

@JoinColumn gives an Entity a foreign key to another Entity whereas @JoinTable will list the relationship between all relationships between Entity A and Entity B. As far as I can tell, they both appear to do similar things. When should I use one or the other?

Answer 1

Let's say you have an entity A which has a @ManyToOne association ot an entity B

@JoinColumn will define the target table Foreign Key (e.g B_ID) while using the target Entity table (e.g. B).

@Entity public class A {      private Long id;      @ManyToOne     @JoinColumn(name="B_ID")     private B b;  } 

@JoinTable will use a separate table to hold the relationship between A and B.

@Entity public class A {      private Long id;      @ManyToOne     @JoinTable(        name = "A_B",         joinColumns = @JoinColumn(name = "B_ID"),         inverseJoinColumns = @JoinColumn(name = "A_ID")     )     private B b;  } 

This time neither A nor B contain any Foreign Key, because there's a separate table (e.g. A_B) to hold the association between A and B.