Hibernate: select max(ID) from T_PARENT
Hibernate: select tparentchi_.PARENT_ID, tparentchi_.ORDER_ID, tparentchi_.CHILD_ID from T_PARENT_CHILD tparentchi_ where tparentchi_.PARENT_ID=? and tparentchi_.ORDER_ID=? and tparentchi_.CHILD_ID=?
Hibernate: select max(ID) from T_CHILD
Hibernate: select tparentchi_.PARENT_ID, tparentchi_.ORDER_ID, tparentchi_.CHILD_ID from T_PARENT_CHILD tparentchi_ where tparentchi_.PARENT_ID=? and tparentchi_.ORDER_ID=? and tparentchi_.CHILD_ID=?
Hibernate: insert into T_PARENT (NAME, ID) values (?, ?)
Hibernate: insert into T_CHILD (NAME, ID) values (?, ?)
Hibernate: insert into T_PARENT_CHILD (PARENT_ID, ORDER_ID, CHILD_ID) values (?, ?, ?)
org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update
   at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:96)
   at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66)
   at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:275)
   at org.hibernate.jdbc.AbstractBatcher.prepareStatement(AbstractBatcher.java:114)
   at org.hibernate.jdbc.AbstractBatcher.prepareStatement(AbstractBatcher.java:109)
   at org.hibernate.jdbc.AbstractBatcher.prepareBatchStatement(AbstractBatcher.java:244)
   at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2393)
   at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2856)
   at org.hibernate.action.EntityInsertAction.execute(EntityInsertAction.java:79)
   at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:273)
   at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:265)
   at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:184)
   at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:321)
   at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:51)
   at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1216)
   at Main.main(Main.java:34)
   at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
   at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
   at java.lang.reflect.Method.invoke(Method.java:597)
   at com.intellij.rt.execution.application.AppMain.main(AppMain.java:115)
Caused by: java.sql.BatchUpdateException: Column 'PARENT_ID' cannot be null
   at com.mysql.jdbc.PreparedStatement.executeBatchSerially(PreparedStatement.java:2007)
   at com.mysql.jdbc.PreparedStatement.executeBatch(PreparedStatement.java:1443)
   at org.hibernate.jdbc.BatchingBatcher.doExecuteBatch(BatchingBatcher.java:70)
   at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:268)
   ... 18 more

CREATE TABLE `T_PARENT`
(
   `ID` INT NOT NULL AUTO_INCREMENT,
   `NAME` VARCHAR(32),
   PRIMARY KEY (`ID`)
) TYPE=MyISAM DEFAULT CHARSET=utf8;

CREATE TABLE `T_CHILD`
(
   `ID` INT NOT NULL AUTO_INCREMENT,
   `NAME` VARCHAR(32),
   PRIMARY KEY (`ID`)
) TYPE=MyISAM DEFAULT CHARSET=utf8;

CREATE TABLE `T_PARENT_CHILD`
(
   `PARENT_ID` INT NOT NULL,
   `CHILD_ID` INT NOT NULL,
   `ORDER_ID` INT NOT NULL,
   PRIMARY KEY (`PARENT_ID`, `CHILD_ID`, `ORDER_ID`),
   INDEX `PARENT_ID` (`PARENT_ID` ASC),
   INDEX `CHILD_ID` (`CHILD_ID` ASC)
) TYPE=MyISAM DEFAULT CHARSET=utf8;


ALTER TABLE `T_PARENT_CHILD` ADD CONSTRAINT `FK_TPC_PARENT`
   FOREIGN KEY (`PARENT_ID`) REFERENCES `T_PARENT` (`ID`);

ALTER TABLE `T_PARENT_CHILD` ADD CONSTRAINT `FK_TPC_CHILD`
   FOREIGN KEY (`CHILD_ID`) REFERENCES `T_CHILD` (`ID`);

  <class name="hibtest.model.TParent" table="T_PARENT">
    <id name="id" type="java.lang.Integer">
      <column name="ID" precision="5" scale="0"/>
      <generator class="increment"/>
    </id>
    <property name="name" type="string">
      <column name="NAME" length="20" not-null="true"/>
    </property>
    <set name="children" cascade="all" inverse="true">
      <key><column name="PARENT_ID" not-null="true"/></key>
      <one-to-many class="hibtest.model.TParentChild"></one-to-many>
    </set>
  </class>

  <class name="hibtest.model.TChild" table="T_CHILD">
    <id name="id" type="java.lang.Integer">
      <column name="ID" precision="5" scale="0"/>
      <generator class="increment"/>
    </id>
    <property name="name" type="string">
      <column name="NAME" length="20" not-null="true"/>
    </property>
    <set name="parent" table="T_PARENT_CHILD">
      <key><column name="CHILD_ID" not-null="true"/></key>
      <one-to-many class="hibtest.model.TParentChild"></one-to-many>
    </set>
  </class>

  <class name="hibtest.model.TParentChild" table="T_PARENT_CHILD">
    <composite-id name="id" class="hibtest.model.TParentChildId">
      <key-property name="parentId" column="PARENT_ID" type="java.lang.Integer" />
      <key-property name="orderId" column="ORDER_ID" type="java.lang.Integer" />
      <key-property name="childId" column="CHILD_ID" type="java.lang.Integer" />
    </composite-id>
    <many-to-one name="parent" insert="false" update="false"
                 column="PARENT_ID" class="hibtest.model.TParent"/>
    <many-to-one name="child" lazy="false" insert="false" update="false"
                 cascade="all" column="CHILD_ID" class="hibtest.model.TChild"/>
  </class>

import hibtest.model.TChild;
import hibtest.model.TParent;
import hibtest.model.TParentChild;
import hibtest.model.TParentChildId;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

import java.util.HashSet;
import java.util.Set;

public class Main {
    private static final SessionFactory ourSessionFactory;

    static {
        try {
            ourSessionFactory = new Configuration().
                    configure("hibernate.cfg.xml").
                    buildSessionFactory();
        } catch (Throwable ex) {
            throw new ExceptionInInitializerError(ex);
        }
    }

    public static Session getSession() throws HibernateException {
        return ourSessionFactory.openSession();
    }

    public static void main(final String[] args) throws Exception {
        final Session session = getSession();
        try {
            session.saveOrUpdate(getParent());
            session.flush();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            session.close();
        }
    }

    private static TParent getParent () {
        TParent parent = new TParent ();
        parent.setName("pname");
        Set<TParentChild> children = new HashSet<TParentChild>();
        children.add(getParentChild(parent, "c1", 1));
        children.add(getParentChild(parent, "c2", 2));
        parent.setChildren(children);
        return parent;
    }

    private static TChild getChild (String name) {
        TChild child = new TChild();
        child.setName(name);
        return child;
    }

    private static TParentChild getParentChild (TParent parent, String childName, Integer order) {
        TParentChild pc = new TParentChild();
        TParentChildId pcId = new TParentChildId();
        pcId.setParentId(parent.getId());
        pcId.setOrderId(order);
        pc.setId(pcId);
        TChild child = getChild(childName);
        Set<TParentChild> parentSet = new HashSet<TParentChild>();
        parentSet.add(pc);
        child.setParent(parentSet);
        pc.setChild(child);
        pc.setParent(parent);
        return pc;
    }
}

  <class name="hibtest.model.TParentChild" table="T_PARENT_CHILD">
    <composite-id name="id" class="hibtest.model.TParentChildId">
      <key-many-to-one name="parent" column="PARENT_ID" class="hibtest.model.TParent"/>
      <key-property name="orderId" column="ORDER_ID" type="java.lang.Integer" />
    </composite-id>
    <many-to-one name="child" lazy="false" fetch="select"
                 cascade="all" column="CHILD_ID" class="hibtest.model.TChild"/>
  </class>