java - JPA Collection Using Map -

so have small proof of concept using jpa, hibernate , spring data. in poc have created post entity , comment entity. post entity contains map of comments map<integer,comment>.

i having issues persisting multiple comment entities map since used comment entities @id column key map. basically, if didn't explicitly set id of comment hibernate recognized them same entity , persisted 1 of them.

i found persist map specifying garbage keys, mysql autonumber replace once persisted. led issue, keys within current map not receive new commentid values set database. caused unit test fail.

so have 3 questions?

1. should specify garbage keys persist entities in map?
2. is approach wrong? if so, whats better way?
3. if garbage keys ok, how can refresh them after insert?

post.java

@entity @table(name = "post") public class post {      @id     @generatedvalue(strategy = generationtype.identity)     @column(name = "post_id")     private integer postid;      @column(name = "title")     private string title;      @onetomany(mappedby = "post", cascade = cascadetype.all)     @mapkeycolumn(name="comment_id")     private map<integer, comment> comments = new hashmap<integer, comment>();          /** accessors (get/set) **/         /** hashcode & equals not consider postid field or map */ } 

comment.java

@entity @table(name="comment") public class comment {      @id     @column(name="comment_id")     @generatedvalue(strategy=generationtype.identity)     private integer commentid;      @column(name="body")     private string body;      @manytoone(cascade=cascadetype.all)     @joincolumn(name="post_id")     private post post;          /** accessors (get/set) **/         /** hashcode & equals not consider commentid field or post */ } 

unit test

@test public void inserttest2(){     comment comment = new comment();     comment comment2 = new comment();     final string body1 = "this map test";     final string body2 = "this map test";      comment.setbody(body1);     comment2.setbody(body2);      post post = new post();     post.setpostdate(new date());     post.settitle("first post");       post.getcomments().put(1,comment);   //setting garbage ids     post.getcomments().put(2, comment2); //setting garbage ids      comment.setpost(post);     comment2.setpost(post);      repository.save(post);      post dbpost = repository.findone(post.getpostid());      map<integer, comment> comments = dbpost.getcomments();      //test fails using old id            asserttrue(comments.containskey(comment.getcommentid()));     //same here      asserttrue(comments.containskey(comment2.getcommentid()));    } 

also note bidirectional relationship

should specify garbage keys persist entities in map?

no. real id affected, map in inconsistent state. keys of map should immutable.

is approach wrong? if so, whats better way?

frankly, don't see point in using map hold comments id. entity manager able comment id. use set or list.

the alternative persist comments , flush entity manager before adding them map, make sure have real id.