java - JPA with Hibernate 4.x, @ElementCollection, Primary Key -

i using jpa hibernate 4.x., , postgresql 9.x, wonder problem.

when using @elementcollection annotation, , configured set type embedded field, expect generate primary key of embeddable collection table, it's not working. can find 1 foreign key against owner of relationship. wonder why not generate primary key. test code. a.java

@entity public class {     @id     private long id;     @column(name = "\"as\"")     private string as;     public string getas() {         return as;     }      public void setas(string as) {         this.as = as;     }      @elementcollection     private set<b> bs = new hashset<>();      public long getid() {         return id;     }      public void setid(long id) {         this.id = id;     }      public set<b> getbs() {         return bs;     }      public void setbs(set<b> bs) {         this.bs = bs;     } } 

b.java

@embeddable public class b {     private string col1;     private string col2;      public string getcol1() {         return col1;     }      public void setcol1(string col1) {         this.col1 = col1;     }      public string getcol2() {         return col2;     }      public void setcol2(string col2) {         this.col2 = col2;     } } 

the result is

hibernate:      create table (         id int8 not null,         "as" varchar(255),         primary key (id)     ) hibernate:      create table a_bs (         a_id int8 not null,         col1 varchar(255),         col2 varchar(255)     ) hibernate:      alter table a_bs          add constraint fk_rcecll1ao3brmwwnsep3iqq3p          foreign key (a_id)          references 

let me know why did not generate primary key? in advance~

because @elementcollection used mapping collections of simple elements, not same entities. thing need reference owning entity generated hibernate (column a_id , foreign key (a_id) references a). take @ this post more information.

if need primary key in embeddable object, consider making proper entity.