MyBatis之自查询使用递归实现 N级联动效果(两种实现方式)

public class TestOne { public int TestSelf(int n){  if(n<0){   throw new IllegalArgumentException("n不能为负数");  }else if(n<=2){   return 1;  }else{   return TestSelf(n-2)+TestSelf(n-1);  } } @Test public void Test(){  System.out.println(TestSelf(30)); }}

public int TestSelfTwo(int n){  if(n<0){   throw new IllegalArgumentException("n不能为负数");  }else if(n<=1){ //递归前两个数 不管n是多少 为一   return 1;  }  int[] nums = new int[n+1]; //30位从零开始  nums[0]=1;  nums[1]=1;  for (int i =2;i<n;i++){   nums[i] = nums[i-2]+nums[i-1];  }  return nums[n-1]; } @Test public void Test(){  System.out.println(TestSelfTwo(30)); }

sql语句：select * from type where pid = 0;  首次指定pid值为0，然后下次根据pid为0的cid 作为下次查询的pid   public List<Category> getCategory(Integer pid); //接口层方法

<mapper namespace="dao.CateGoryDao"> <resultMap id="getSelf" type="entity.Category">   <id column="cid" property="cid"></id>   <result column="cname" property="cName"></result>   <collection property="categorySet" select="getCategory" column="cid"></collection> //这里可以不用指定oftype 使用反向查询select从另一个maper文件中取出数据时必须用ofType   <!--查到的cid作为下次的pid--> </resultMap> <select id="getCategory" resultMap="getSelf" >  select * from category where pid=#{pid} </select></mapper>

package entity;import java.util.HashSet;import java.util.Set;/** * Created by zhangyu on 2017/7/12. */public class Category { private Integer cid; private String cName; private Integer pid; private Set<Category> categorySet = new HashSet<Category>(); @Override public String toString() {  return "Category{" +    "cid=" + cid +    ", cName='" + cName + '/'' +    ", pid=" + pid +    ", categorySet=" + categorySet +    '}'; } public Integer getCid() {  return cid; } public void setCid(Integer cid) {  this.cid = cid; } public String getcName() {  return cName; } public void setcName(String cName) {  this.cName = cName; } public Integer getPid() {  return pid; } public void setPid(Integer pid) {  this.pid = pid; } public Set<Category> getCategorySet() {  return categorySet; } public void setCategorySet(Set<Category> categorySet) {  this.categorySet = categorySet; }}

 //测试自连接 @Test public void TestSelf(){  CateGoryDao dao = MyBatis.getSessionTwo().getMapper(CateGoryDao.class);  List<Category> list = dao.getCategory(0);  for (Category item:list ) {   System.out.println(item);  } }

Category{cid=1, cName='图书', pid=0, categorySet=[Category{cid=5, cName='期刊报纸', pid=1, categorySet=[]}, Category{cid=3, cName='青年图书', pid=1, categorySet=[Category{cid=6, cName='读者', pid=3, categorySet=[Category{cid=7, cName='12月份', pid=6, categorySet=[]}]}]}, Category{cid=4, cName='少儿图书', pid=1, categorySet=[]}]}Category{cid=2, cName='服装', pid=0, categorySet=[]}