请教:这样查询如何处理?

实体:File
id  | parentid | filesize
1   |    0     |   100
2   |    1     |   75
3   |    1     |   25
4   |    2     |   50
5   |    2     |   25
6   |    5     |   20
7   |    6     |   5
1、求出所有id号为1的所有子对象数据（如上例显示包括：2,3,4,5,6,7）；
2、更新所有id号为1的所有子对象的filesize为0

比如同时更新子对象\子对象的子对象\....
应如何高效的处理呢?

这个问题看见好几次了，今天动手尝试了一下，这里是源程序：
Databas scheme:

use test;
drop table if exists file;
create table file(
    id int NOT NULL AUTO_INCREMENT,
    parentid int,
    filesize int NOT NULL DEFAULT 0,
    PRIMARY KEY (id);,
    INDEX (parentid);,
    FOREIGN KEY (parentid); REFERENCES file(id); ON DELETE CASCADE
);;
insert into file(id, filesize); values (1, 100);;
insert into file(id, parentid, filesize); values (2, 1, 75);;
insert into file(id, parentid, filesize); values (3, 1, 25);;
insert into file(id, parentid, filesize); values (4, 2, 50);;
insert into file(id, parentid, filesize); values (5, 2, 25);;
insert into file(id, parentid, filesize); values (6, 5, 20);;
insert into file(id, parentid, filesize); values (7, 6, 5);;

hibernate-mapping:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping
    PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>
    <class name="file.File" table="file">
        <id name="id" column="id" type="int" unsaved-value="null" >
            <generator class="identity"/>
        </id>
        <property name="parentID" column="parentid" type="int" not-null="false" insert="false" update="false"/>
        <property name="filesize" column="filesize" type="int" not-null="true"  />
        <many-to-one name="parent" column="parentid" update="false" not-null="false"/>
        <bag name="childs" inverse="true" lazy="false" cascade="all-delete-orphan" >
            <key column="parentid"/>
            <one-to-many class="file.File"/>
        </bag>
    </class>
</hibernate-mapping>

PO:

package file;

import java.util.List;
import java.util.ArrayList;

public class File {
    private Integer id;
    private Integer parentID;
    private Integer filesize;
    private File parent;
    private List children = new ArrayList();;

    public File(); {
    }

    public File(Integer fileSize); {
        this.filesize = fileSize;
    }

    public File(int size); {
        this.filesize = new Integer(size);;
    }

    public Integer getId(); {
        return id;
    }

    public void setId(Integer id); {
        this.id = id;
    }

    public Integer getParentID(); {
        return parentID;
    }

    public void setParentID(Integer parentID); {
        this.parentID = parentID;
    }

    public Integer getFilesize(); {
        return filesize;
    }

    public void setFilesize(Integer filesize); {
        this.filesize = filesize;
    }

    public File getParent(); {
        return parent;
    }

    public void setParent(File parent); {
        this.parent = parent;
    }

    public List getChildren(); {
        return children;
    }

    public void setChildren(List children); {
        this.children= children;
    }

    public void addChild(File child); {
        child.setParent(this);;
        this.children.add(child);;
    }

    public void printTree(); {
        System.out.println("ID: " + id + "\t" + "Parent: " + "\t" + "Filesize: " + filesize);;
        for (int i = 0; i < children.size();; i++); {
            ((File);children.get(i););.printTree();;
        }
    }

    public void resetFilesize(); {
        this.filesize = new Integer(0);;
        for (int i = 0; i < children.size();; i++); {
            ((File);children.get(i););.resetFilesize();;
        }
    }
}

DAO这里就省略了。如需要，我可以附上全部代码，包括ant build和junit test case.

database: MySQL, table type: InnoDB

为了便于大家读程序，再加上junit test case:

package file;

import junit.framework.TestCase;
import net.sf.hibernate.HibernateException;

public class TestFile extends TestCase {

    FileDAO fileDAO = new FileDAO();;
    File file1;
    File file2;
    File file3;

    public void setUp(); {
        file1 = new File(100);;
        file2 = new File(200);;
        file3 = new File(300);;
        file2.addChild(file3);;
        file1.addChild(file2);;
        try {
            fileDAO.saveFile(file1);;
        } catch (HibernateException e); {
            e.printStackTrace();;
            fail();;
        }
    }

    public void testSave(); {
        assertTrue(file1.getId();.intValue(); > 0);;
        assertTrue(file2.getId();.intValue(); > 0);;
        assertTrue(file3.getId();.intValue(); > 0);;
    }

    public void testDelete(); {
        Integer id1 = file1.getId();;
        Integer id2 = file2.getId();;
        Integer id3 = file1.getId();;
        try {
            fileDAO.deleteFile(file1);;
        } catch (HibernateException e); {
            e.printStackTrace();;
            fail();;
        }
        try {
            fileDAO.loadFile(id1);;
            fail("File1 should be deleted");;
        } catch (HibernateException e); {
        }

        try {
            fileDAO.loadFile(id2);;
            fail("File2 should be deleted");;
        } catch (HibernateException e); {
        }
        try {
            fileDAO.loadFile(id3);;
            fail("File3 should be deleted");;
        } catch (HibernateException e); {
        }
    }

    public void testLoad(); {
        try {
            File theFile1 = fileDAO.loadFile(file1.getId(););;
            File theFile2 = (File); theFile1.getChildren();.get(0);;
            File theFile3 = (File); theFile2.getChildren();.get(0);;
            assertTrue(theFile1.getId();.equals(file1.getId();););;
            assertTrue(theFile2.getId();.equals(file2.getId();););;
            assertTrue(theFile3.getId();.equals(file3.getId();););;
            theFile1.printTree();;
        } catch (HibernateException e); {
            e.printStackTrace();;
            fail();;
        }
    }

    public void testResetFilesize(); {
        file1.resetFilesize();;
        try {
            fileDAO.updateFile(file1);;
            File theFile1 = fileDAO.loadFile(file1.getId(););;
            File theFile2 = (File); theFile1.getChildren();.get(0);;
            File theFile3 = (File); theFile2.getChildren();.get(0);;
            assertTrue(theFile1.getFilesize();.intValue(); == 0);;
            assertTrue(theFile2.getFilesize();.intValue(); == 0);;
            assertTrue(theFile3.getFilesize();.intValue(); == 0);;
            theFile1.printTree();;
        } catch (HibernateException e); {
            e.printStackTrace();;
            fail();;
        }
    }

    public void tearDown(); {
        try {
            fileDAO.deleteFile(file1);;
        } catch (HibernateException e); {
            e.printStackTrace();;
        }
    }
}