java - Hibernate GenericJDBCException : Field 'KeyID' doesn't have a default value -

hi trying create 1 many relationship string object different key id on same table.

but when insert data show exception "general error message server: "field 'qid' doesn't have default value".

how resolve problem in hibernate. please refer below code.

     <class name="com.db.hrquestion" table="hrquestion">       <id name="id">       <generator class="increment"></generator>       </id>       <property name="qname"></property>       <list name="answers" table="answer">         <key column="qid"></key>         <index column="type"></index>         <element column="answer" type="string"></element>       </list>        </class>       <class name="com.db.javaquestion" table="javaquestion">         <id name="id">             <generator class="increment"></generator>          </id>         <property name="qname"></property>          <list name="answers" table="answer">              <key column="java_qid"></key>             <index column="type"></index>             <element column="answer" type="string"></element>         </list>      </class> 

java code :

 javaquestion javaquestion= new javaquestion(); javaquestion.setqname("what meant java?"); arraylist<string> javaanswerlist=new arraylist<string>(); javaanswerlist.add("java object oriented programming "); javaanswerlist.add("java platform independent"); javaquestion.setanswers(javaanswerlist);  hrquestion hrquestion=new hrquestion(); hrquestion.setqname("hr question one"); arraylist<string> list2=new arraylist<string>(); list2.add("my profile ....."); list2.add("my objetcive..."); hrquestion.setanswers(list1);  session.save(javaquestion); session.save(hrquestion); 

as map 2 lists of answers same table, have define both key column qid , java_qid nullable.

<key column="qid" not-null="false"></key> .... <key column="java_qid" not-null="false"></key>