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:
[code:1]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);
[/code:1]

hibernate-mapping:
[code:1]
<?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>
[/code:1]

PO:
[code:1]
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();
        }
    }
}
[/code:1]

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:
[code:1]
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();
        }
    }
}[/code:1]