java - jpa/hibernate one-to-one mapping -

        package com.sow.dao;          import java.io.serializable;          import javax.persistence.cascadetype;         import javax.persistence.column;         import javax.persistence.entity;         import javax.persistence.generatedvalue;         import javax.persistence.generationtype;         import javax.persistence.id;         import javax.persistence.joincolumn;         import javax.persistence.onetoone;         import javax.persistence.table;         import javax.xml.bind.annotation.xmlrootelement;          @xmlrootelement         @entity         @table(name = "empcre")         public class empauth implements serializable {             @id             @generatedvalue             @column(name = "id", unique = true, nullable = false)             int id;             @column(name = "username")             string username;             @column(name = "userpwd")             string pwd;             @onetoone(mappedby = "empcre")             @joincolumn(name = "id")             private empdetails empdetails;              public int getid() {                 return id;             }              public void setid(int id) {                 this.id = id;             }              public string getusername() {                 return username;             }              public void setusername(string username) {                 this.username = username;             }              public string getpwd() {                 return pwd;             }              public void setpwd(string pwd) {                 pwd = pwd;             }              public empdetails getempdetails() {                 return empdetails;             }              public void setempdetails(empdetails empdetails) {                 this.empdetails = empdetails;             }          }              package com.sow.dao;      import javax.persistence.column;     import javax.persistence.entity;     import javax.persistence.generatedvalue;     import javax.persistence.id;     import javax.persistence.joincolumn;     import javax.persistence.onetoone;     import javax.persistence.table;      import org.hibernate.annotations.genericgenerator;     import org.hibernate.annotations.parameter;      @entity     @table(name = "empdetails")     @genericgenerator(name = "person-primarykey", strategy = "foreign", parameters = { @parameter(name = "property", value = "empcre") })     public class empdetails {         @id         @generatedvalue(generator = "person-primarykey")         // @genericgenerator(name = "gen", strategy = "foreign", parameters =         // @parameter(name = "property", value = "empcre"))         @column(name = "id", unique = true, nullable = false)         int id;          @column(name = "empname")         string empname;         @column(name = "address")         string address;         @column(name = "empsal")         string empsal;          @onetoone()         @joincolumn(name = "id")         private empauth empcre;          public empauth getempcre() {             return empcre;         }          public void setempcre(empauth empcre) {             this.empcre = empcre;         }          public int getid() {             return id;         }          public void setid(int id) {             this.id = id;         }          public string getempname() {             return empname;         }          public void setempname(string empname) {             this.empname = empname;         }          public string getaddress() {             return address;         }          public void setaddress(string address) {             this.address = address;         }          public string getempsal() {             return empsal;         }          public void setempsal(string empsal) {             this.empsal = empsal;         }      } 

error

 severe: servlet.service() servlet [jersey-serlvet] in context path [/restdemo] threw exception     org.hibernate.id.identifiergenerationexception: attempted assign id null one-to-one property [com.sow.dao.empdetails.empcre]         @ org.hibernate.id.foreigngenerator.generate(foreigngenerator.java:101)         @ org.hibernate.event.internal.abstractsaveeventlistener.savewithgeneratedid(abstractsaveeventlistener.java:120)         @ org.hibernate.event.internal.defaultmergeeventlistener.savetransiententity(defaultmergeeventlistener.java:422)         @ org.hibernate.event.internal.defaultmergeeventlistener.mergetransiententity(defaultmergeeventlistener.java:342)         @ org.hibernate.event.internal.defaultmergeeventlistener.entityistransient(defaultmergeeventlistener.java:304)         @ org.hibernate.event.internal.defaultmergeeventlistener.onmerge(defaultmergeeventlistener.java:259)         @ org.hibernate.event.internal.defaultmergeeventlistener.onmerge(defaultmergeeventlistener.java:86)         @ org.hibernate.internal.sessionimpl.firemerge(sessionimpl.java:781)         @ org.hibernate.internal.sessionimpl.merge(sessionimpl.java:766)         @ org.hibernate.internal.sessionimpl.merge(sessionimpl.java:770)         @ com.sow.userservice.newemp(userservice.java:100)         @ sun.reflect.nativemethodaccessorimpl.invoke0(native method)         @ sun.reflect.nativemethodaccessorimpl.invoke(nativemethodaccessorimpl.java:57)         @ sun.reflect.delegatingmethodaccessorimpl.invoke(delegatingmethodaccessorimpl.java:43)         @ java.lang.reflect.method.invoke(method.java:606)         @ com.sun.jersey.spi.container.javamethodinvokerfactory$1.invoke(javamethodinvokerfactory.java:60)         @ com.sun.jersey.server.impl.model.method.dispatch.abstractresourcemethoddispatchprovider$typeoutinvoker._dispatch(abstractresourcemethoddispatchprovider.java:185)         @ com.sun.jersey.server.impl.model.method.dispatch.resourcejavamethoddispatcher.dispatch(resourcejavamethoddispatcher.java:75)         @ com.sun.jersey.server.impl.uri.rules.httpmethodrule.accept(httpmethodrule.java:288)         @ com.sun.jersey.server.impl.uri.rules.righthandpathrule.accept(righthandpathrule.java:147)         @ com.sun.jersey.server.impl.uri.rules.resourceclassrule.accept(resourceclassrule.java:108)         @ com.sun.jersey.server.impl.uri.rules.righthandpathrule.accept(righthandpathrule.java:147)         @ com.sun.jersey.server.impl.uri.rules.rootresourceclassesrule.accept(rootresourceclassesrule.java:84)         @ com.sun.jersey.server.impl.application.webapplicationimpl._handlerequest(webapplicationimpl.java:1469)         @ com.sun.jersey.server.impl.application.webapplicationimpl._handlerequest(webapplicationimpl.java:1400)         @ com.sun.jersey.server.impl.application.webapplicationimpl.handlerequest(webapplicationimpl.java:1349)         @ com.sun.jersey.server.impl.application.webapplicationimpl.handlerequest(webapplicationimpl.java:1339)         @ com.sun.jersey.spi.container.servlet.webcomponent.service(webcomponent.java:416)         @ com.sun.jersey.spi.container.servlet.servletcontainer.service(servletcontainer.java:537)         @ com.sun.jersey.spi.container.servlet.servletcontainer.service(servletcontainer.java:699)         @ javax.servlet.http.httpservlet.service(httpservlet.java:727)         @ org.apache.catalina.core.applicationfilterchain.internaldofilter(applicationfilterchain.java:303)         @ org.apache.catalina.core.applicationfilterchain.dofilter(applicationfilterchain.java:208)         @ org.apache.tomcat.websocket.server.wsfilter.dofilter(wsfilter.java:52)         @ org.apache.catalina.core.applicationfilterchain.internaldofilter(applicationfilterchain.java:241)         @ org.apache.catalina.core.applicationfilterchain.dofilter(applicationfilterchain.java:208)         @ org.apache.catalina.core.standardwrappervalve.invoke(standardwrappervalve.java:220)         @ org.apache.catalina.core.standardcontextvalve.invoke(standardcontextvalve.java:122)         @ org.apache.catalina.authenticator.authenticatorbase.invoke(authenticatorbase.java:503)         @ org.apache.catalina.core.standardhostvalve.invoke(standardhostvalve.java:170)         @ org.apache.catalina.valves.errorreportvalve.invoke(errorreportvalve.java:103)         @ org.apache.catalina.valves.accesslogvalve.invoke(accesslogvalve.java:950)         @ org.apache.catalina.core.standardenginevalve.invoke(standardenginevalve.java:116)         @ org.apache.catalina.connector.coyoteadapter.service(coyoteadapter.java:421)         @ org.apache.coyote.http11.abstracthttp11processor.process(abstracthttp11processor.java:1070)         @ org.apache.coyote.abstractprotocol$abstractconnectionhandler.process(abstractprotocol.java:611)         @ org.apache.tomcat.util.net.jioendpoint$socketprocessor.run(jioendpoint.java:316)         @ java.util.concurrent.threadpoolexecutor.runworker(threadpoolexecutor.java:1145)         @ java.util.concurrent.threadpoolexecutor$worker.run(threadpoolexecutor.java:615)         @ org.apache.tomcat.util.threads.taskthread$wrappingrunnable.run(taskthread.java:61)         @ java.lang.thread.run(thread.java:744) 

i trying achieve one-to-one relationship unidirectional using foreign key in associated table. while inserting date, inserting data in primary key table giving error insert above error.

you using primary key join column.

in @onetoone, joincolumn column references other side of relationship. since id primary key column, shouldn't use foreign key column (it's name of referencing column, not referenced column).

change joincolumn emp_id (or remove default value.)

the exception caused way hibernate persists relationships, first inserts both sides of relationship, , update create relationship. here, update on primary key column, fails.