java - How to insert foreign key references into database with JPA? -

in company model there employee superclass (it has public setter & getter methods):

@entity @inheritance @discriminatorcolumn(name="emp_type") @table(name="employees") public abstract class employee implements printable, serializable {      @id     @generatedvalue     @column(name = "employee_id", unique = true)     private int id;      @column(name = "position")     @enumerated(enumtype.string)     private position position;      @column(name = "name")     private string name;      @column(name = "salary")     private double salary;      @transient     public list<project> projectsworkingon = new arraylist<>();      public employee() {     } } 

there 2 subclasses worker, leader extending employee, , 5 other classes extending this, e.g.: developerleader:

@entity @discriminatorvalue("dl") public class developerleader extends leader {      public developerleader() {     } } 

i have project class, has 3 worker types:

@entity @table(name = "projects") public class project implements printable, serializable {      @id     @generatedvalue     @column(name = "project_id", unique = true)     private int id;      private string name;     private double budget;      @onetoone(cascade = {cascadetype.all})     @joincolumn(name="consultantleader_id", updatable = false, insertable = false)     private consultantleader consultantleader;      @onetoone(cascade = {cascadetype.all})     @joincolumn(name="developerleader_id", updatable = false, insertable = false)     private developerleader developerleader;      @onetoone(cascade = {cascadetype.all})     @joincolumn(name="projectleader_id", updatable = false, insertable = false)     private projectleader projectleader;      public project() {     } } 

the problem is, i'm trying reference leader types in project class, when running main class, every time i've tried add project db, got following error:

java.lang.illegalstateexception: org.hibernate.transientpropertyvalueexception: object references unsaved transient instance - save transient instance beforequery flushing org.hibernate.transientpropertyvalueexception: object references unsaved transient instance - save transient instance beforequery flushing

that's why i've added cascade = {cascadetype.all} @onetoone annotation. problem now, annotation, inserts leaders every time again in database, when i'm inserting new project, furthermore leaders not in database in right columns in project row (they empty).. how can solve this?