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=[]}