merge - Spring-Data JPA: save new entity referencing existing one -

the question same below one:

jpa cascade persist , references detached entities throws persistentobjectexception. why?

i'm creating new entity references existing, detached one. when save entity in spring data repository exception thrown:

org.springframework.dao.invaliddataaccessapiusageexception: detached entity passed persist 

if @ save() method in source code of spring data jpa see:

public <s extends t> s save(s entity) {      if (entityinformation.isnew(entity)) {         em.persist(entity);         return entity;     } else {         return em.merge(entity);     } } 

and if @ isnew() in abstractentityinformation

public boolean isnew(t entity) {      return getid(entity) == null; } 

so if save() new entity (id == null), spring data call persist , hence scenario fail.

this seems typical use case when adding new items collections.

how can resolve this?

edit 1:

note:

this issue not directly related how save new entity refers existing entity in spring jpa?. elaborate assume request create new entity on http. extract information request , create entity , existing referenced one. hence detached.

i had similar issue trying save new entity object saved entity object inside.

what did implemented persistable< t > , implemented isnew() accordingly.

public class myentity implements persistable<long> {      public boolean isnew() {         return null == getid() &&             subentity.getid() == null;     } 

or use abstractpersistable , override isnew there ofcourse.

i don't know if considered way of handling issue worked out quite me , besides feels natural do.