class Characteristic {
	int id;
	String name;

	//getters/setters
}

class CharacteristicValue {
	int id;
	Characteristic characteristic;
	String value;

	public CharacteristicValue(String value, Characteristic characteristic) {
		this.value = value;
		this.characteristic = characteristic;
	}

	//getters/setters
}


public void addCharacteristicValue(String value, Characteristic characteristic) {
	Session sesion = factory.openSession();
	Transaction t = null;

	try {
		CharacteristicValue value = new CharacteristicValue(value, characteristic);
		t = session.beginTransaction();
		session.save(value);
		t.commit();		
	} catch(Exception ex) {
		if (t != null) {t.rollback();}
		ex.printStackTrace();
	} finally {
		session.close();
	}
}

session.save(value);

<hibernate-mapping>
    <class name="Characteristic" table="CHARACTERISTIC">
        <id name="id" column="ID">
            <generator class="native"/>
        </id>

        <property name="name" column="NAME" type="string"/>
    </class>
</hibernate-mapping>

<hibernate-mapping>
    <class name="CharacteristicValue" table="CHARACTERISTIC_VALUE">
        <id name="id" column="ID">
            <generator class="native"/>
        </id>

        <property name="value" column="VALUE" type="string"/>


        <many-to-one name="characteristic" column="CHARACTERISTIC_ID" class="Characteristic" unique="true"
                     not-null="true" lazy="false"/>
    </class>
</hibernate-mapping>

CREATE TABLE public.characteristic_value (
  id INTEGER PRIMARY KEY NOT NULL,
  value CHARACTER VARYING(255),
  characteristic_id INTEGER NOT NULL,
  idx INTEGER,
  FOREIGN KEY (characteristic_id) REFERENCES characteristic (id)
  MATCH UNKNOWN ON UPDATE NO ACTION ON DELETE NO ACTION
);
CREATE UNIQUE INDEX uk_hwaanymqg2t9grhc2ko9migl0 ON characteristic_value USING BTREE (characteristic_id);


CREATE TABLE public.characteristic (
  id INTEGER PRIMARY KEY NOT NULL,
  name CHARACTER VARYING(255),
  idx INTEGER
);

<many-to-one name="characteristic" column="CHARACTERISTIC_ID" class="Characteristic" unique="true"
                     not-null="true" lazy="false"/>

<many-to-one name="characteristic" column="CHARACTERISTIC_ID" class="Characteristic" not-null="true"
                     lazy="false"/>