java - 公式延迟加载不起作用

Question

我正在寻找从实体检索计算字段。

我有一个 Customer 实体，我想知道客户订购的总订单，但我需要延迟加载获取，因此我希望在 时计算“totalOrders”字段调用 Customer.getTotalOrders()。

使用以下配置，延迟加载不起作用，并且总是计算总订单数。我做错了什么？

客户实体上的 XML 映射:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.tumrapp.entities.Customer" table="customers">
        <id name="id" type="java.lang.Integer">
            <column name="id" />
            <generator class="identity" />
        </id>

        <property name="name" type="string">
            <column name="name" not-null="true" />
        </property>

        <property update="false" insert="false" name="totalOrders" type="int" lazy="true"
            formula="(select count(o.id) from orders o where o.customer_id = id)">
        </property>

    </class>
</hibernate-mapping>

客户实体类:

public class Customer implements java.io.Serializable {

    private static final long serialVersionUID = 1L;
    private Integer id;
    private String name;
    private Integer totalOrders;

    //constructors
    //simple getters and setters
}

Hibernate 控制台上显示的查询:

select
    customer0_.id as id61_0_,
    customer0_.name as name61_0_,
    (select
        count(o.id) 
    from
        orders o 
    where
        o.customer_id = customero0_.id) as formula1_0_ 
from
    customer customer0_ 
where
    customer0_.id=?

Answer 1

公式将始终在初始 select 上进行计算，并且惰性属性将被默默忽略，除非您为实体类添加字节码检测(例如通过 Ant/Maven )。对于一对一连接也是如此。