MyBatis-映射树数据结构

Question

How can I map table id | parent_id | name id | parent_id | name id | parent_id | name to my pojo class:

public class Node {
  private Integer id;
  private Integer parentId;
  private String name;
  private List<Node> children;
  //getters and setters
}

I want to get list of root nodes (parent_id=null) with filled children list. No restriction in tree depth. I am thinking of something like:

<resultMap id="nodeResult" type="Node">
  <id property="id" column="id"/>
  <result property="parentId" column="parent_id"/>
  <result property="name" column="name"/>
  <collection property="children" resultMap="nodeResult"/>
</resultMap>
<select id="selectNode" resultMap="nodeResult">
  SELECT * FROM NODE
</select>

I don't know where to put restriction for children list: id=parentId. I don't want to use nested select

Answer 1

There won't be a way to get an arbitrarly deep tree to populate automagically in a ResultMap.

Are DB specific solutions an option? For example, with PostgreSQL you can use common table expressions to select the data into a ResultSet that may be applicable to be mapped into a tree.

Otherwise you should just change your collection definition in the ResultMap to point to a query to select the children, which can reuse the same resultmap to get the recursive behavior