hibernate執行表與表之間多對一的查詢時,如果數據庫中沒有數據時,一切正常,一旦將數據插入到數據庫中,查詢的時候將會拋出空指針異常。以下是我的*.hbm.xml的配置
<?xml version="1.0" encoding="utf-8"?>
<!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.song.entity.Album" table="album" catalog="photosystem">
<id name="albumId" type="java.lang.Integer" column="albumId">
<generator class="identity" />
</id>
<property name="albumName" type="java.lang.String" column="albumName" />
<property name="albumDesc" type="java.lang.String" column="albumDesc" />
<property name="createDate" type="java.lang.String" column="createDate" />
<property name="cover" type="java.lang.String" column="cover" />
<many-to-one name="user" column="userId" class="com.song.entity.User" />
<many-to-one name="kind" column="kindId" class="com.song.entity.Kind" />
<set name="photos" inverse="true">
<key column="albumId" />
<one-to-many class="com.song.entity.Photo"/>
</set>
</class>
</hibernate-mapping>
後來經過多方查證,需要在配置文件中的多對一的查詢中加入Lazy="false".需要修改的地方爲:
<many-to-one name="user" column="userId" class="com.song.entity.User" lazy="false"/>
<many-to-one name="kind" column="kindId" class="com.song.entity.Kind" lazy="false"/>
但我有個疑問啊,lazy的默認就是false,不寫的話就會報錯,寫上就不拋空指針異常,這是問什麼呢??求證。。。。。。