基于注解自身OneToMany
直接看代码：
package net.mai123.bean;import java.util.List;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.OneToMany;import javax.persistence.Table;@Entity@Table(name="TYPE_INF")public class TypeInf {@Id@Column(name="TYPE_ID")private int typeId;@Column(name="TYPE_NAME")private String typeName;@Column(name="PARENT_ID")private int parentId;@OneToMany(targetEntity=TypeInf.class)@JoinColumn(name="PARENT_ID")private List<TypeInf> childrens;@Column(name="SHOWABLE")private int showAble;@Column(name="REMARK")private String remark;public int getTypeId() {return typeId;}/************* 省略掉setter和getter **************/}DROP TABLE IF EXISTS TYPE_INF;CREATE TABLE TYPE_INF(TYPE_ID INT AUTO_INCREMENT PRIMARY KEY,TYPE_NAME VARCHAR(40),PARENT_ID INT,SHOWABLE INT DEFAULT 0,REMARK VARCHAR(400));
package net.mai123.dao.impl;import java.util.List;import net.mai123.bean.TypeInf;public class TypeInfDao extends CommonDao<TypeInf> {/************* 省略掉无关的代码 **************/@SuppressWarnings("unchecked")public List<TypeInf> doQuery() {//加上select distinct是为了去除重复的parent//left join fetch 可以不延迟加载List<TypeInf> lst = find("select distinct t from TypeInf t left join fetch t.childrens where t.parentId=0");for(TypeInf t : lst){System.out.println(t.getTypeName()+":"+t.getChildrens().size());}return lst;}}Hibernate: select distinct typeinf0_.TYPE_ID as TYPE1_1_0_, childrens1_.TYPE_ID as TYPE1_1_1_, typeinf0_.PARENT_ID as PARENT2_1_0_, typeinf0_.REMARK as REMARK1_0_, typeinf0_.SHOWABLE as SHOWABLE1_0_, typeinf0_.TYPE_NAME as TYPE5_1_0_, childrens1_.PARENT_ID as PARENT2_1_1_, childrens1_.REMARK as REMARK1_1_, childrens1_.SHOWABLE as SHOWABLE1_1_, childrens1_.TYPE_NAME as TYPE5_1_1_, childrens1_.PARENT_ID as PARENT2_0__, childrens1_.TYPE_ID as TYPE1_0__ from TYPE_INF typeinf0_ left outer join TYPE_INF childrens1_ on typeinf0_.TYPE_ID=childrens1_.PARENT_ID where typeinf0_.PARENT_ID=0家具/日用品:6二手笔记本:13电子数码:6图书/音乐/运动 :5家用电器:9台式电脑/网络:4服饰/箱包/化妆品:6商用/办公:4闲置礼品:3手机/通讯相关:5母婴/儿童用品:5