public class User {
 
	private Integer id;
 	private String name;
 	private Set<Order> orders=new  HashSet<Order>();
	
 	public Set<Order> getOrders() {
 		return orders;
 	}

	 public void setOrders(Set<Order> orders) {
	 this.orders = orders;
	 }
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	
	public User() {
		
	}
	public User(Integer id, String name) {
		
		this.id = id;
		this.name = name;
	}
}

public class Order  {
	 
	private Integer id;
	private Integer id_user;
	private String item;

	public Order() {
	}
		
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public Integer getId_user() {
		return id_user;
	}
	public void setId_user(Integer id_user) {
		this.id_user = id_user;
	}
	public String getItem() {
		return item;
	}
	public void setItem(String item) {
		this.item = item;
	}
	 	
}

<hibernate-mapping>
    <class name="com.mycompany.User" table="USERS">
        <id name="id" type="java.lang.Integer">
            <column name="ID" />
            <generator class="identity" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="NAME" length="20" />
        </property>
       <set name="orders" table="ORDERS" inverse="true" lazy="true" fetch="select">
            <key>
                <column name="ID" not-null="true" />
            </key>
            <one-to-many class="com.mycompany.Order" />
        </set>
    </class>
</hibernate-mapping>

<hibernate-mapping>
    <class name="com.mycompany.Order" table="ORDERS">
        <id name="id" type="java.lang.Integer">
            <column name="ID" />
            <generator class="identity" />
        </id>
       
        <property name="id_user" type="java.lang.Integer">
            <column name="ID_USER" />
        </property>
       
        <property name="item" type="java.lang.String">
            <column name="ITEM" />
        </property>
       
    </class>
</hibernate-mapping>