JPA：保留地图<String,Entity>

Question

Could you help to persist a Map when String is not the key of the Entity mapped? For example:

class A {

   @Id
   long id;

   String code;
}

class B {

   @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true, fetch = FetchType.EAGER)
   @What magical combination of JPA annotations should I use here?! 
   Map<String,A> mapAByCode;

}

I've tried a lot of combinations of {@JoinTable,@MapKeyColumn,@JoinColumn,@JoinTable} annotations with no success and I'm going crazy...

Thanks!

Answer 1

Since you seem to want to map your entities using the A.code value, @MapKey is what you are after. @MapKey allows you to define the value within the reference to use as the key for the map. As the javadoc states, it is required to be unique though or you will run into problems.

  @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true, fetch = FetchType.EAGER)
  @MapKey(name="code")
  Map<String,A> mapAByCode;

Answer 2

It seems that the problem is related to other map I'm using in the same class:

@Entity
class A {

  @Id
  long id;

  String code;
}

@Entity
class B {

    @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true, fetch = FetchType.EAGER)
    @JoinTable(name = "B_MAPABYID", joinColumns = @JoinColumn(name = "B_ID"))
    @MapKey(name="id")
    Map<Long,A> mapAById;

    @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true, fetch = FetchType.EAGER)
    @JoinTable(name = "B_MAPABYCODE", joinColumns = @JoinColumn(name = "B_ID"))
    @MapKey(name="code")
    Map<String,A> mapAByCode;

}

This configuration is not working for me, but if I set mapAById as transient all works fine. Does it makes any sense for you?