java - Hibernate:复合元素导致每次提交时删除+插入

Question

这是我的映射的一部分:

<hibernate-mapping package="trx.domain">
    <class name="Master" table="master" dynamic-update="true" dynamic-insert="true">

        <set name="attributes" table="attribute" lazy="true"
            cascade="all" batch-size="10">
            <cache usage="nonstrict-read-write" />
            <key>
                <column name="master_id" />
            </key>
            <composite-element class="Attribute">
                <many-to-one name="type" class="AttributeType"
                     not-null="true" column="attribute_type_id" lazy="false" />
                <property name="value">
                    <column name="value" />
                </property>
            </composite-element>
        </set>
    </class>
</hibernate-mapping>

如果我只是扫描 attributes 集，没有任何更新，Hibernate 仍然会在提交时执行一批 delete 和 insert 操作。

Hibernate: delete from attribute where master_id=? and attribute_type_id=?
Hibernate: delete from attribute where master_id=? and attribute_type_id=?
Hibernate: insert into attribute (master_id, attribute_type_id, value) values (?, ?, ?)
Hibernate: insert into attribute (master_id, attribute_type_id, value) values (?, ?, ?)

为什么会这样？如何预防？

Answer 1

根据 Hibernate Reference

Because of the structure of a Set, Hibernate does not UPDATE a row when an element is "changed". Changes to a Set always work via INSERT and DELETE of individual rows.

如果 Hibernate 尝试更新您的集合，即使您不修改它，也许您在 Attribute 类中的 equals 和 hashcode 实现是坏了？