database - Java JPA - Persisting @OneToMany entity -

hello everyone,

i'm having these days problem persisting object @onetomany. having problem i'm trying create both objects (one onetomany, other 1 manytoone), , want persist @onetomany one, , automatically have @manytoone persisted database also. (all tables set autoincrement, , collection initialized in constructor of komponenta.class, i've put parts connected problem). here's code:

public class komponenta implements serializable {  @id private integer idkom;  @onetomany(cascade = cascadetype.all, mappedby = "idkom") private collection<ima> imacollection = new arraylist<>();  }  public class ima implements serializable {  @id private integer idima;  @joincolumn(name = "idkom", referencedcolumnname = "idkom") @manytoone private komponenta idkom;  }      // runnable part     tools.em.gettransaction().begin();      komponenta k = new komponenta();     ima = new ima();      collection<ima> list = k.getimacollection();     list.add(i);     k.setimacollection(list);            i.setidkom(k);      tools.em.persist(k);     tools.em.gettransaction().commit(); 

i'm getting type of error console output:

internal exception: com.mysql.jdbc.exceptions.jdbc4.mysqlintegrityconstraintviolationexception: column 'idkom' cannot null error code: 1048

to use mysql auto_increment column, supposed use identity strategy:

@id @generatedvalue(strategy=generationtype.identity) private integer idkom; 

which you'd when using auto mysql:

@id @generatedvalue(strategy=generationtype.auto) private integer idkom; 

which equivalent to

@id @generatedvalue private integer idkom;