hibernate 的left join fetch可以取出lazy对象，如果lazy的是Set，还想对Set里面对象进行继续Fetch他的成员怎么办呢？

Question

->刚才做了个例子试了一下,
->当你使用from Category c left join fetch c.childCategories as c1的时候
->childCategories里面的对象已经载入了,不需要再去写一个外联接后来想想c1其实是Collection，而不是Category了->感觉c1在hql里面不是Collection而是一个Category对象,你可以在where里面用c1.Category的属性=值  来定义查询条件的

Answer 1

:)，谢谢，不过你似乎理解错了，第一层的Collection里面确实是Category，已经取出来了，但这是个嵌套的需求，Collection里面的Category也一样还有Cellection，我是接着往里嵌套的取不出来了，比如第一层是爷爷，2层是父亲，3层是孙子，那么通过爷爷连接是可以把父亲那一辈取出来，但是这辈人的儿子们怎么取呢？

Answer 2

对每一个孩子集合使用Hibernate.initialize(parent.getChildren());
感觉好像没有别的好办法，呵呵

Answer 3

我觉得单靠left join取所有的子孙(虽然楼主只想取到孙子层)是行不通的.

Answer 4

from Father f left join fetch f.son as s left join fetch s.grandson as gHibernate: select father0_.father_id as father1_0_, son1_.son_id as son1_1_, grandson2_.grand_id as grand1_2_, father0_.name as name0_0_, son1_.name as name1_1_, son1_.fatherId as fatherId1_1_, son1_.fatherId as fatherId0__, son1_.son_id as son1_0__, grandson2_.grandsonName as grandson2_2_2_, grandson2_.sonId as sonId2_2_, grandson2_.sonId as sonId1__, grandson2_.grand_id as grand1_1__ from father father0_ left outer join son son1_ on father0_.father_id=son1_.fatherId left outer join grandson grandson2_ on son1_.son_id=grandson2_.sonId这是生成的sql

Answer 5

在同一张表里面没有试过,代码主干贴出来看一下,我得下层是一个集合<?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.softbrain.wangzl.hibernate.children.Father" table="father">
<id name="fatherId" column="father_id">
<generator class="increment">
</generator>
</id>
<property name="fatherName" column="name">
</property>

<set name="son" table="son" inverse="true" cascade="all" lazy="true">
<key>
<column name="fatherId">
</column>
</key>
<one-to-many class="com.softbrain.wangzl.hibernate.children.Son"></one-to-many>
</set>
</class>
</hibernate-mapping>public class Father {
    private Set son = new HashSet();
    private Integer fatherId;
    private String fatherName = null;
    
    /**
     * @return Returns the fatherId.
     */
    public Integer getFatherId() {
        return fatherId;
    }
    /**
     * @param fatherId The fatherId to set.
     */
    public void setFatherId(Integer fatherId) {
        this.fatherId = fatherId;
    }
    /**
     * @return Returns the fatherName.
     */
    public String getFatherName() {
        return fatherName;
    }
    /**
     * @param fatherName The fatherName to set.
     */
    public void setFatherName(String fatherName) {
        this.fatherName = fatherName;
    }
    /**
     * @return Returns the son.
     */
    public Set getSon() {
        return son;
    }
    /**
     * @param son The son to set.
     */
    public void setSon(Set son) {
        this.son = son;
    }
}

Answer 6

<?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.softbrain.wangzl.hibernate.children.Son" table="son">
<id name="sonId" column="son_id">
<generator class="increment">
</generator>
</id>
<property name="sonName" column="name">
</property>

<set name="grandson" table="grandson" inverse="true" cascade="all" lazy="true">
<key>
<column name="sonId">
</column>
</key>
<one-to-many class="com.softbrain.wangzl.hibernate.children.Grandson"></one-to-many>
</set>

<many-to-one name="father" class="com.softbrain.wangzl.hibernate.children.Father" column="fatherId">
</many-to-one>
</class>
</hibernate-mapping>public class Son {
    private Set grandson = new HashSet();
    private Father father = null;
    /**
     * @return Returns the father.
     */
    public Father getFather() {
        return father;
    }
    /**
     * @param father The father to set.
     */
    public void setFather(Father father) {
        this.father = father;
    }
    private Integer sonId;
    private Integer fatherId;
    private String sonName = null;
    
    /**
     * @return Returns the fatherId.
     */
    public Integer getFatherId() {
        return fatherId;
    }
    /**
     * @param fatherId The fatherId to set.
     */
    public void setFatherId(Integer fatherId) {
        this.fatherId = fatherId;
    }
    /**
     * @return Returns the grandson.
     */
    public Set getGrandson() {
        return grandson;
    }
    /**
     * @param grandson The grandson to set.
     */
    public void setGrandson(Set grandson) {
        this.grandson = grandson;
    }
    /**
     * @return Returns the sonId.
     */
    public Integer getSonId() {
        return sonId;
    }
    /**
     * @param sonId The sonId to set.
     */
    public void setSonId(Integer sonId) {
        this.sonId = sonId;
    }
    
    /**
     * @return Returns the sonname.
     */
    public String getSonName() {
        return sonName;
    }
    /**
     * @param sonname The sonname to set.
     */
    public void setSonName(String sonName) {
        this.sonName = sonName;
    }
}

Answer 7

<?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.softbrain.wangzl.hibernate.children.Grandson" table="grandson">
<id name="grandsonId" column="grand_id">
<generator class="increment">
</generator>
</id>
<property name="grandsonName">
</property>
<many-to-one name="son" class="com.softbrain.wangzl.hibernate.children.Son" column="sonId">
</many-to-one>
</class>
</hibernate-mapping>public class Grandson {
    private Integer grandsonId;
    private Integer sonId;
    private String grandsonName = null;
    private Son son = null;
    
    /**
     * @return Returns the son.
     */
    public Son getSon() {
        return son;
    }
    /**
     * @param son The son to set.
     */
    public void setSon(Son son) {
        this.son = son;
    }    /**
     * @return Returns the sonId.
     */
    public Integer getSonId() {
        return sonId;
    }
    /**
     * @param sonId The sonId to set.
     */
    public void setSonId(Integer sonId) {
        this.sonId = sonId;
    }
    /**
     * @return Returns the grandsonId.
     */
    public Integer getGrandsonId() {
        return grandsonId;
    }
    /**
     * @param grandsonId The grandsonId to set.
     */
    public void setGrandsonId(Integer grandsonId) {
        this.grandsonId = grandsonId;
    }
    /**
     * @return Returns the grandsonName.
     */
    public String getGrandsonName() {
        return grandsonName;
    }
    /**
     * @param grandsonName The grandsonName to set.
     */
    public void setGrandsonName(String grandsonName) {
        this.grandsonName = grandsonName;
    }
}

Answer 8

Configuration conf = new Configuration().configure();
        SessionFactory sf = conf.buildSessionFactory();
        
        Session session = sf.openSession();
        Transaction t = session.beginTransaction();
        
//        Father father = new Father();
//        father.setFatherName("father");
//        
//        Son son1 = new Son();
//        Son son2 = new Son();
//        son1.setSonName("son1");
//        son1.setFather(father);
//        son2.setSonName("son2");
//        son2.setFather(father);
//        
//        Grandson grandson1 = new Grandson();
//        Grandson grandson2 = new Grandson();
//        Grandson grandson3 = new Grandson();
//        Grandson grandson4 = new Grandson();
//        
//        grandson1.setGrandsonName("grandson1");
//        grandson1.setSon(son1);
//        grandson2.setGrandsonName("grandson2");
//        grandson2.setSon(son1);
//        grandson3.setGrandsonName("grandson3");
//        grandson3.setSon(son2);
//        grandson4.setGrandsonName("grandson4");
//        grandson4.setSon(son2);
//        
//        son1.getGrandson().add(grandson1);
//        son1.getGrandson().add(grandson2);
//        son2.getGrandson().add(grandson3);
//        son2.getGrandson().add(grandson4);
//        
//        father.getSon().add(son1);
//        father.getSon().add(son2);
//        
//        session.save(father);
//        t.commit();
        
        String hql = "from Father f left join fetch f.son as s left join fetch s.grandson as g";
        
        Query query = session.createQuery(hql);
        
        List list = query.list(); 
        Son son = ((Son)(((Father)list.get(0)).getSon().toArray()[0]));
        Grandson grandson = (Grandson) son.getGrandson().toArray()[0];
        
        System.out.println(grandson.getGrandsonName());