Mybatis自查询递归查找子菜单

之前写过 java从数据库读取菜单，递归生成菜单树

今天才发现mybatis也可以递归查询子菜单

先看一下数据库

主键id，名称name，父id，和url

设计菜单类

public class Menu {
    // 菜单id
    private String id;
    // 父菜单id
    private String parentId;
    // 菜单名称
    private String name;
    // 菜单url
    private String url;
    // 子菜单
    private List<Menu> children;
    // 省去getter setter和toString方法
}

menuDao

public interface MenuDao {

    /**
     * 递归查找所有
     *
     * @return
     */
    public List<Menu> findAllRecursion();
}

mapper.xml

 <resultMap type="Menu" id="recursionMenuMap">
        <id column="id" property="id"/>
        <result column="name" property="name"/>
        <collection property="children" ofType="Menu" column="id" select="findMenuByParentId"/>
    </resultMap>

    <select id="findAllRecursion" resultMap="recursionMenuMap">
        SELECT id,`name`,parent_id,url FROM menu WHERE parent_id ='' or parent_id is NULL ORDER BY `order` ASC
    </select>

    <select id="findMenuByParentId" resultType="Menu">
        SELECT id,`name`,parent_id,url FROM menu WHERE parent_id = #{id} ORDER BY `order` ASC
    </select>

其中findAllRecursion会查询到所有的父菜单，

因为我们定义的

<select id="findAllRecursion" resultMap="recursionMenuMap">

而在recursionMenuMap中我们定义了如何去查找子菜单，调用findMenuByParentId