Java hibernate-减少查询的数量
一个产品可以有一个或多个子产品形成树状结构。子产品也将引用父产品。在我的测试代码中,我创建了一个家长(Java hibernate-减少查询的数量,java,hibernate,Java,Hibernate,一个产品可以有一个或多个子产品形成树状结构。子产品也将引用父产品。在我的测试代码中,我创建了一个家长(mortgage)和两个孩子(ml和me)。为什么我尝试加载父级Product entity=(Product)hibernateTemplate.get(Product.class,mortgage.getId())它正在正确使用连接 然而,hibernate也在尝试加载ml和me的子项,即使它们都没有任何子项。有没有办法避免这种情况,这样我就可以将查询的数量从3个减少到1个 生成的SQL使用
mortgage
)和两个孩子(ml和me
)。为什么我尝试加载父级Product entity=(Product)hibernateTemplate.get(Product.class,mortgage.getId())代码>它正在正确使用连接
然而,hibernate也在尝试加载ml和me
的子项,即使它们都没有任何子项。有没有办法避免这种情况,这样我就可以将查询的数量从3个减少到1个
生成的SQL使用动态生成的别名,如children0\u0
。有没有办法让hibernate使用我自己的别名说“p”
这是我的hbm和测试代码
hbm
<class name="Product" table="PRODUCT">
<id name="id" type="java.lang.Long" column="ID">
<generator class="native">
<param name="sequence">PRODUCT_SN</param>
</generator>
</id>
<many-to-one name="parent" class="Product" lazy="false" column="PARENT" />
<set name="children" lazy="false" fetch="join" table="PRODUCT" cascade="all">
<key>
<column name="PARENT" />
</key>
<one-to-many class="Product" />
</set>
<property name="code" type="java.lang.String" column="CODE" not-null="true" />
<property name="name" type="java.lang.String" column="NAME" />
<property name="startDate" type="java.util.Date" column="STARTDATE" />
<property name="endDate" type="java.util.Date" column="ENDDATE" />
<property name="decisionable" type="boolean" column="ISDECISIONABLE" />
<property name="selectable" type="boolean" column="ISSELECTABLE" />
</class>
日志
Hibernate: select product0_.ID as ID0_1_, product0_.PARENT as PARENT0_1_, product0_.CODE as CODE0_1_, product0_.NAME as NAME0_1_, product0_.STARTDATE as STARTDATE0_1_, product0_.ENDDATE as ENDDATE0_1_, product0_.ISDECISIONABLE as ISDECISI7_0_1_, product0_.ISSELECTABLE as ISSELECT8_0_1_, children1_.PARENT as PARENT3_, children1_.ID as ID3_, children1_.ID as ID0_0_, children1_.PARENT as PARENT0_0_, children1_.CODE as CODE0_0_, children1_.NAME as NAME0_0_, children1_.STARTDATE as STARTDATE0_0_, children1_.ENDDATE as ENDDATE0_0_, children1_.ISDECISIONABLE as ISDECISI7_0_0_, children1_.ISSELECTABLE as ISSELECT8_0_0_ from PRODUCT product0_ left outer join PRODUCT children1_ on product0_.ID=children1_.PARENT where product0_.ID=?
DEBUG [org.hibernate.type.LongType] binding '1' to parameter: 1
DEBUG [org.hibernate.type.LongType] returning '2' as column: ID0_0_
DEBUG [org.hibernate.type.LongType] returning '1' as column: PARENT0_0_
DEBUG [org.hibernate.type.StringType] returning 'Mortgage Loan' as column: CODE0_0_
DEBUG [org.hibernate.type.StringType] returning null as column: NAME0_0_
DEBUG [org.hibernate.type.TimestampType] returning null as column: STARTDATE0_0_
DEBUG [org.hibernate.type.TimestampType] returning null as column: ENDDATE0_0_
DEBUG [org.hibernate.type.BooleanType] returning 'false' as column: ISDECISI7_0_0_
DEBUG [org.hibernate.type.BooleanType] returning 'false' as column: ISSELECT8_0_0_
DEBUG [org.hibernate.type.LongType] returning null as column: PARENT0_1_
DEBUG [org.hibernate.type.StringType] returning 'Mortgage' as column: CODE0_1_
DEBUG [org.hibernate.type.StringType] returning null as column: NAME0_1_
DEBUG [org.hibernate.type.TimestampType] returning null as column: STARTDATE0_1_
DEBUG [org.hibernate.type.TimestampType] returning null as column: ENDDATE0_1_
DEBUG [org.hibernate.type.BooleanType] returning 'false' as column: ISDECISI7_0_1_
DEBUG [org.hibernate.type.BooleanType] returning 'false' as column: ISSELECT8_0_1_
DEBUG [org.hibernate.type.LongType] returning '1' as column: PARENT3_
DEBUG [org.hibernate.type.LongType] returning '2' as column: ID3_
DEBUG [org.hibernate.type.LongType] returning '3' as column: ID0_0_
DEBUG [org.hibernate.type.LongType] returning '1' as column: PARENT0_0_
DEBUG [org.hibernate.type.StringType] returning 'Home Equity LOC' as column: CODE0_0_
DEBUG [org.hibernate.type.StringType] returning null as column: NAME0_0_
DEBUG [org.hibernate.type.TimestampType] returning null as column: STARTDATE0_0_
DEBUG [org.hibernate.type.TimestampType] returning null as column: ENDDATE0_0_
DEBUG [org.hibernate.type.BooleanType] returning 'false' as column: ISDECISI7_0_0_
DEBUG [org.hibernate.type.BooleanType] returning 'false' as column: ISSELECT8_0_0_
DEBUG [org.hibernate.type.LongType] returning '1' as column: PARENT3_
DEBUG [org.hibernate.type.LongType] returning '3' as column: ID3_
Hibernate: select children0_.PARENT as PARENT1_, children0_.ID as ID1_, children0_.ID as ID0_0_, children0_.PARENT as PARENT0_0_, children0_.CODE as CODE0_0_, children0_.NAME as NAME0_0_, children0_.STARTDATE as STARTDATE0_0_, children0_.ENDDATE as ENDDATE0_0_, children0_.ISDECISIONABLE as ISDECISI7_0_0_, children0_.ISSELECTABLE as ISSELECT8_0_0_ from PRODUCT children0_ where children0_.PARENT=?
DEBUG [org.hibernate.type.LongType] binding '3' to parameter: 1
Hibernate: select children0_.PARENT as PARENT1_, children0_.ID as ID1_, children0_.ID as ID0_0_, children0_.PARENT as PARENT0_0_, children0_.CODE as CODE0_0_, children0_.NAME as NAME0_0_, children0_.STARTDATE as STARTDATE0_0_, children0_.ENDDATE as ENDDATE0_0_, children0_.ISDECISIONABLE as ISDECISI7_0_0_, children0_.ISSELECTABLE as ISSELECT8_0_0_ from PRODUCT children0_ where children0_.PARENT=?
DEBUG [org.hibernate.type.LongType] binding '2' to parameter: 1
您可能应该将关系标记为lazy,以便仅在必要时加载子对象。
如果要加载节点及其子节点,请使用专用查询:
select p from Product left join fetch p.children where p.id = :id
我认为你看到所有孩子的原因是你在
中定义了fetch=“join”
。如果你把它去掉,我想Hibernate只会拉产品
,我不希望他们懒惰。我只是想知道是否有办法告诉hibernate抑制最后两个sql。不,如果要抑制它们,应该使用延迟抓取。您可以在模型中配置它,也可以将其配置为此特定查询的获取配置文件(以便它在应用程序中的任何其他地方都可以使用)。
select p from Product left join fetch p.children where p.id = :id