mybatis 父子级树形结构查询

针对父子级数据目录查询, 以前都是逐级的去根据父级id查询子集目录, 查出后最后再在代码中拼成树形结构, 相当复杂,我们可以利用 mybatis 提供的 collection 标签自动组织树形结构, 接下来我们一步一步看该如何建立

1.建表语句

CREATE TABLE `parent_child` (`id` int(11) NOT NULL AUTO_INCREMENT,`name` varchar(255) NOT NULL,`parent_id` int(11) DEFAULT NULL COMMENT '父级id',`create_time` varchar(32) NOT NULL,PRIMARY KEY (`id`) USING BTREE,KEY `index_parent_child_id` (`id`) USING BTREE,KEY `index_type_name` (`name`) USING BTREE,KEY `index_parent_id` (`parent_id`) USING BTREE
) ENGINE=InnoDB AUTO_INCREMENT=23 DEFAULT CHARSET=utf8 ROW_FORMAT=DYNAMIC;INSERT INTO `parent_child` VALUES ('1', '0-1', '0', '2022-09-13 11:59:13');
INSERT INTO `parent_child` VALUES ('2', '0-2', '0', '2022-09-13 11:59:28');
INSERT INTO `parent_child` VALUES ('3', '0-3', '0', '2022-09-13 14:01:20');
INSERT INTO `parent_child` VALUES ('4', '1-1', '1', '2022-09-13 14:01:41');
INSERT INTO `parent_child` VALUES ('5', '1-2', '1', '2022-09-13 14:01:58');
INSERT INTO `parent_child` VALUES ('6', '1-3', '1', '2022-09-13 14:02:11');
INSERT INTO `parent_child` VALUES ('7', '2-1', '2', '2022-09-13 14:02:24');
INSERT INTO `parent_child` VALUES ('8', '2-2', '2', '2022-09-13 14:02:49');
INSERT INTO `parent_child` VALUES ('9', '2-3', '2', '2022-09-13 14:03:03');
INSERT INTO `parent_child` VALUES ('10', '3-1', '3', '2022-09-13 14:03:16');
INSERT INTO `parent_child` VALUES ('11', '3-2', '3', '2022-09-13 14:03:28');
INSERT INTO `parent_child` VALUES ('12', '3-3', '3', '2022-09-13 14:03:39');
INSERT INTO `parent_child` VALUES ('13', '1-1-1', '4', '2022-09-13 14:04:05');
INSERT INTO `parent_child` VALUES ('14', '1-1-2', '4', '2022-09-13 14:04:19');
INSERT INTO `parent_child` VALUES ('15', '1-3-1', '6', '2022-09-29 14:04:34');
INSERT INTO `parent_child` VALUES ('16', '1-3-2', '6', '2022-09-13 14:04:45');
INSERT INTO `parent_child` VALUES ('17', '3-2-1', '11', '2022-09-13 14:05:07');
INSERT INTO `parent_child` VALUES ('18', '3-2-2', '11', '2022-09-13 14:05:22');
INSERT INTO `parent_child` VALUES ('19', '3-3-1', '12', '2022-09-13 14:05:37');
INSERT INTO `parent_child` VALUES ('20', '3-2-1-1', '17', '2022-09-30 14:06:02');
INSERT INTO `parent_child` VALUES ('21', '3-2-1-1-1', '20', '2022-09-13 14:06:19');
INSERT INTO `parent_child` VALUES ('22', '3-2-1-1-2', '20', '2022-09-09 14:06:36');

2.建立返回数据结构 VO

get set方法这里省略自行补上就行

public class ParentChildVo {private Integer id;private String name;private Integer parentId;private Date createTime;private List<ParentChildVo> children;
}

3.mybatis 编写查询语句

3.1 mapper文件:

    /***  查询树形目录* @param parentId* @return*/List<ParentChildVo> getParentChildTree(int parentId);

3.2 mybatis文件

  <!-- 树形结构 --><resultMap id="ParentChildTreeMap" type="com.ashen.game.common.vo.ParentChildVo"><id column="id" jdbcType="VARCHAR" property="id" /><id column="name" jdbcType="VARCHAR" property="name" /><id column="parentId" jdbcType="INTEGER" property="parentId" /><id column="createTime" jdbcType="VARCHAR" property="createTime" /><collection property="children" ofType="com.ashen.game.common.vo.ParentChildVo" column="id" select="getParentChildTree" fetchType="eager"/></resultMap><!--查询树形分组--><select id="getParentChildTree" resultMap="ParentChildTreeMap">SELECTa.id,a.name,a.parent_id as  parentId,a.create_time as createTimeFROM parent_child AS aWHEREa.parent_id = #{parentId}</select>

3.3 查询结果

{"data": [{"id": 1,"name": "0-1","parentId": 0,"createTime": "2022-09-13 11:59:13","children": [{"id": 4,"name": "1-1","parentId": 1,"createTime": "2022-09-13 14:01:41","children": [{"id": 13,"name": "1-1-1","parentId": 4,"createTime": "2022-09-13 14:04:05","children": []},{"id": 14,"name": "1-1-2","parentId": 4,"createTime": "2022-09-13 14:04:19","children": []}]},{"id": 5,"name": "1-2","parentId": 1,"createTime": "2022-09-13 14:01:58","children": []},{"id": 6,"name": "1-3","parentId": 1,"createTime": "2022-09-13 14:02:11","children": [{"id": 15,"name": "1-3-1","parentId": 6,"createTime": "2022-09-29 14:04:34","children": []},{"id": 16,"name": "1-3-2","parentId": 6,"createTime": "2022-09-13 14:04:45","children": []}]}]},{"id": 2,"name": "0-2","parentId": 0,"createTime": "2022-09-13 11:59:28","children": [{"id": 7,"name": "2-1","parentId": 2,"createTime": "2022-09-13 14:02:24","children": []},{"id": 8,"name": "2-2","parentId": 2,"createTime": "2022-09-13 14:02:49","children": []},{"id": 9,"name": "2-3","parentId": 2,"createTime": "2022-09-13 14:03:03","children": []}]},{"id": 3,"name": "0-3","parentId": 0,"createTime": "2022-09-13 14:01:20","children": [{"id": 10,"name": "3-1","parentId": 3,"createTime": "2022-09-13 14:03:16","children": []},{"id": 11,"name": "3-2","parentId": 3,"createTime": "2022-09-13 14:03:28","children": [{"id": 17,"name": "3-2-1","parentId": 11,"createTime": "2022-09-13 14:05:07","children": [{"id": 20,"name": "3-2-1-1","parentId": 17,"createTime": "2022-09-30 14:06:02","children": [{"id": 21,"name": "3-2-1-1-1","parentId": 20,"createTime": "2022-09-13 14:06:19","children": []},{"id": 22,"name": "3-2-1-1-2","parentId": 20,"createTime": "2022-09-09 14:06:36","children": []}]}]},{"id": 18,"name": "3-2-2","parentId": 11,"createTime": "2022-09-13 14:05:22","children": []}]},{"id": 12,"name": "3-3","parentId": 3,"createTime": "2022-09-13 14:03:39","children": [{"id": 19,"name": "3-3-1","parentId": 12,"createTime": "2022-09-13 14:05:37","children": []}]}]}],"message": "ok","code": 0,"count": null,"token": null
}

4.常见报错

服务处理异常:

Type definition error: [simple type, class org.apache.ibatis.executor.loader.javassist.JavassistProxyFactory$EnhancedResultObjectProxyImpl];
nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class org.apache.ibatis.executor.loader.javassist.JavassistProxyFactory$EnhancedResultObjectProxyImpl and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS)
(through reference chain: com.dataojo.docloud.model.vo.ResultMap[\"data\"]->java.util.ArrayList[0]->com.dataojo.docloud.model.vo.DirectoryGroupTreeVo_$$_jvstb9_0[\"children\"]->java.util.ArrayList[0]->com.dataojo.docloud.model.vo.DirectoryGroupTreeVo_$$_jvstb9_0[\"children\"]->java.util.ArrayList[0]->com.dataojo.docloud.model.vo.DirectoryGroupTreeVo_$$_jvstb9_0[\"handler\"])

报错原因：在mabatis中sql查询时，使用了进行一对多的查询，而collection默认的为懒加载，所以导致return 给前端时报错, 加上 fetchType=“eager” 即可。

完整示例代码

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mybatis 父子级树形结构查询

1.建表语句

2.建立返回数据结构 VO

3.mybatis 编写查询语句

3.1 mapper文件:

3.2 mybatis文件

3.3 查询结果

4.常见报错

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