java - Reusing Persistence Context in JPA -

i working on @embededid code, want auto increment before entity persisted, want without use of @generatedvalue , identity column,

below table composite id,

create table tbl_employee_002(     id integer,      country varchar(50),     name varchar(50),     constraint pk_emp_00240 primary key(id,country) ) 

this code entity mapping,

@entity @table(name="tbl_employee_002") public class employeeentitysix implements serializable{  // contructor's      @embeddedid         private employeeidtwo id;      @column(name="name")     private string employeename;  // getters , setter's      @prepersist     public void incid(){         entitymanager em = null;         query q = null;        entitymanagerfactory emf = null;         try{             emf = persistence.createentitymanagerfactory("forpractise");             em = emf.createentitymanager();             q = em.createquery("select max(e.id.employeeid) employeeentitysix e");             list list = q.getresultlist();             integer = (list != null && list.size() > 0) ? integer.valueof(list.get(0).tostring()) : 0;             this.getid().setemployeeid(++i);         }catch(exception e){             system.out.println("excetion while increasing counter...");             e.printstacktrace();         }finally{             if(em != null && em.isopen()){                 em.close();             }             if(getemf() != null && getemf().isopen()){                 getemf().close();             }         }   } 

this composite id mapping,

@embeddable public class employeeidtwo implements serializable{       @column(name="id")      private integer employeeid;      @column(name="country",length=50)     private string empcountry;  // getters , setters      } 

this code of main method, main method in other class,

public static void main(string [] args){     entitymanagerfactory emf = null;     entitymanager em = null;     entitytransaction tx = null;     try{         emf = persistence.createentitymanagerfactory("forpractise");         em = emf.createentitymanager();         tx = em.gettransaction();                     tx.begin();     employeeentitysix employee = new employeeentitysix(new employeeidtwo("zimbabwe"), "henry olanga");     em.persist(employee); .... } 

now above code runs fine, whenever persist entity "employeeentitysix", method annotated @perpersist runs, first fetch max id, increments its, set id in embeded entity , persist entity.

now question is,

i creating entitymanagerfactory twice, first in main method, second time in @prepersist method in entity employeeentitysix. whether can use first entitymanagerfactory created in main method in entity employeeentitysix while pre-persist, or else whether can reuse entitymanager created in first time in main method in @prepersist method in entity.

just information, using plain java environment, not using java ee container.

hibernate default tries persist fields of entity class or embedded id, including field emf, not know how persist field of type entitymanagerfactory.

of course not make sense persist entitymanagerfactory. mark field @transient prevent being persisted, going face different problems.

the injection of entitymanagerfactory @persistenceunit annotation works on cdi beans , ejbs in applications run on java ee-compliant application server. using main method, assume example simple jse program.

furthermore should not access entitymanagers in lifecycle callback methods such @prepersist. quote jpa specification (jsr 317: javatm persistence api, version 2.0):

in general, lifecycle method of portable application should not invoke entitymanager or query operations, access other entity instances, or modify relationships within same persistence context. lifecycle callback method may modify non-relationship state of entity on invoked.

i suggest keep entitymanagerfactory out of embedded id class , rid of incid-method. instead execute query determine new employeeid in main method, before calling persist. works fine long 1 instance of program works database. when there multiple programs trying insert new employees there race conditions 2 programs try insert same id.

in order prevent can use database sequence generate employeeid, annotations @generatedvalue , @sequencegenerator. find more information id generation here: http://en.wikibooks.org/wiki/java_persistence/identity_and_sequencing#sequencing