mybatis递归查询所有子节点总结

查找所有资讯种类，并将他们映射到对应节点中，然后找出子节点，返给前端。

数据库结构：

NewsType：

public class NewsType{

   private String TypeId;
   private String ParentId;
   private String TypeName;
   private String State;
   private String SortNum;
   private String parentTypeName;

   public String getTypeId() {
      return TypeId;
   }

   public void setTypeId(String typeId) {
      TypeId = typeId;
   }

   public String getParentId() {
      return ParentId;
   }

   public void setParentId(String parentId) {
      ParentId = parentId;
   }

   public String getTypeName() {
      return TypeName;
   }

   public void setTypeName(String typeName) {
      TypeName = typeName;
   }

   public String getState() {
      return State;
   }

   public void setState(String state) {
      State = state;
   }

   public String getSortNum() {
      return SortNum;
   }

   public void setSortNum(String sortNum) {
      SortNum = sortNum;
   }

   public String getParentTypeName() {
      return parentTypeName;
   }

   public void setParentTypeName(String parentTypeName) {
      this.parentTypeName = parentTypeName;
   }
}

NewsTypeCustom：

public class NewsTypeCustom extends NewsType{
    private List children;

    public List getChildren() {
        return children;
    }

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

xml文件中，如下代码所示 ：

id="findAllRecursion" resultMap="recursionNewsTypeMap">
    SELECT * FROM tblnewstype WHERE  ParentId ='' or ParentId is NULL ORDER BY `SortNum` ASC


id="findNewsByParentId" resultMap="recursionNewsTypeMap">
    SELECT * FROM tblnewstype WHERE ParentId = #{TypeId} ORDER BY `SortNum` ASC


id="recursionNewsTypeMap" type="NewsTypeCustom">
    column="TypeId" property="TypeId"/>
    column="ParentId" property="ParentId"/>
    column="TypeName" property="TypeName"/>
    column="State" property="State"/>
    column="SortNum" property="SortNum"/>
    property="children" ofType="NewsTypeCustom"
                column="TypeId" select="findNewsByParentId">
    

注：

特别注意递归，要两个select标签都是这一个resultmap，第一个是查找根节点，第二个是递归查找节点 。

serviceimpl中，如下代码所示 ：

@Override
public List findAllLeafNewsTypes() {
    List newsTypesList = null;
    List finalNewsTypesList = new ArrayList<>();
    List newsTypesTree = appNewsMapper.findAllRecursion();
    for (NewsTypeCustom newsTypeCustom:newsTypesTree) {
        System.out.println("One Traversal");
        if(newsTypeCustom.getParentId() == null || newsTypeCustom.getParentId() == "") {
            System.out.println("newsTypeRootNode:" + newsTypeCustom.toString());
            newsTypesList = getLeafNode(newsTypeCustom.getChildren());
        }
        for (NewsTypeCustom finalnewsTypeCustom:newsTypesList) {
            finalNewsTypesList.add(finalnewsTypeCustom);
        }
    }
    return finalNewsTypesList;
}

/**
 * 获取资讯父节点下面的所有子节点
 * @param NewsTypeCustomList
 * @return List<NewsTypeCustom>
 */
public static List getLeafNode( List NewsTypeCustomList){
    List newsTypeLeafNode = new ArrayList<>();
    for(NewsTypeCustom newsTypeCustom: NewsTypeCustomList){
        System.out.println("One ChildTraversal:"+newsTypeCustom.toString());
        //子节点为空的话，add进叶子节点集合
        if(newsTypeCustom.getChildren().size() != 0){
            System.out.println("newsTypeCustom.getChildren()!!!!!"+newsTypeCustom.getChildren());
                newsTypeLeafNode.addAll(getLeafNode(newsTypeCustom.getChildren()));
        }else{
            //递归遍历下一级
            newsTypeLeafNode.add(newsTypeCustom);
        }
    }
    return newsTypeLeafNode;
}

注：

同样，注意在静态方法中的递归，一定要每一次都将得出的子节点加入到newsTypeLeafNode中（我在写的时候忘掉了，发现只有根节点下面的子节点，而没有将孙子等节点纳入集合中 ） 。

newsTypeLeafNode.addAll(getLeafNode(newsTypeCustom.getChildren()));

不要写成：

getLeafNode(newsTypeCustom.getChildren());