Mysql闭包表之关于国家区域的一个实践

在电商系统中，我们总是会遇到一些树形结构数据的存储需求。如地理区域、位置信息存储，地理信息按照层级划分，会分为很多层级，就拿中国的行政区域划分为例，简单的省-市-县-镇-村就要五个级别。如果系统涉及到跨境的国际贸易，那么存储的地理信息层级会更加深。那么如何正确合理地存储这些数据，并且又能很好的适应各种查询场景就成了我们需要考虑的问题，这次我们来考虑通过闭包表方案，来达到我们的存储及查询需求。

一、设计闭包表

闭包表由Closure Table翻译而来，通过父节点、子节点、两节点距离来描述一棵树空间换时间的思想，Closure Table，一种更为彻底的全路径结构，分别记录路径上相关结点的全展开形式。能明晰任意两结点关系而无须多余查询，级联删除和结点移动也很方便。但是它的存储开销会大一些，除了表示结点的Meta信息，还需要一张专用的关系表。

区域基础信息表结构如下

CREATE TABLE `area_base` (
  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT COMMENT '自增主键',
  `area_name` varchar(50) NOT NULL COMMENT '区域名称',
  `sequence` int(11) DEFAULT NULL COMMENT '排序号，越小越靠前',
  `created_by` bigint(20) NOT NULL COMMENT '创建人',
  `created_time` bigint(20) NOT NULL COMMENT '创建时间',
  `updated_by` bigint(20) DEFAULT NULL COMMENT '更新人',
  `updated_time` bigint(20) NOT NULL DEFAULT '0' COMMENT '更新时间',
  `is_del` tinyint(2) NOT NULL DEFAULT '0' COMMENT '状态：0 正常，-1 已删除',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=56 DEFAULT CHARSET=utf8mb4 COMMENT='区域表';

区域之间指向关系的闭包表结构如下

CREATE TABLE `area_closure` (
`id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '自增长Id',
`ancestor` bigint(20) NOT NULL COMMENT '祖先',
`descendant` bigint(20) NOT NULL COMMENT '后代',
`distance` int(11) DEFAULT NULL COMMENT '祖先到后代之间的距离',
PRIMARY KEY (`id`),
UNIQUE KEY `id_ancedesc` (`ancestor`,`descendant`) USING BTREE,
KEY `idx_ancestor` (`ancestor`,`distance`) USING BTREE,
KEY `idx_descendant` (`descendant`,`distance`) USING BTREE
) ENGINE=InnoDB AUTO_INCREMENT=259 DEFAULT CHARSET=utf8mb4 COMMENT='区域的树形结构闭包表';

模拟一些示范数据，如下所示

mysql> select * from area_base;
+----+-----------+----------+------------+----------------+------------+---------------+--------+
| id | area_name | sequence | created_by | created_time   | updated_by | updated_time  | is_del |
+----+-----------+----------+------------+----------------+------------+---------------+--------+
|  1 | 根节点    |        0 |        123 | 15679841561561 |        990 | 1539175879690 |      0 |
| 29 | 亚洲      |       96 |        123 | 15679841561561 |        990 | 1540031478909 |      0 |
| 30 | 美洲      |       33 |        123 | 15679841561561 |        990 | 1540031478923 |      0 |
| 31 | 欧洲      |        0 |        123 | 15679841561561 |        990 | 1539175879690 |      0 |
| 35 | 中国      |        0 |        123 | 15679841561561 |        990 | 1539175879690 |      0 |
| 36 | 日本      |        0 |        123 | 15679841561561 |        990 | 1539175879690 |      0 |
| 37 | 朝鲜      |        0 |        123 | 15679841561561 |        990 | 1539175879690 |      0 |
| 38 | 广东省    |        0 |        123 | 15679841561561 |        990 | 1539175879690 |      0 |
| 39 | 新疆省    |        0 |        123 | 15679841561561 |        990 | 1539175879690 |      0 |
| 40 | 广西省    |        0 |        123 | 15679841561561 |        990 | 1539175879690 |      0 |
| 41 | 深圳市    |        0 |        123 | 15679841561561 |        990 | 1539175879690 |      0 |
| 42 | 广州市    |        0 |        123 | 15679841561561 |        990 | 1539175879690 |      0 |
| 43 | 佛山市    |        0 |        123 | 15679841561561 |        990 | 1539175879690 |      0 |
+----+-----------+----------+------------+----------------+------------+---------------+--------+
13 rows in set

二、闭包表中的递归操作

如何递归构造出一颗全区域的返回树

    public AreaTreeResponse getAreaTree(Long areaId) {
        String cacheKey = BasicConst.Cache.AREA_TREE_KEY + BasicConst.AreaInfo.ROOT_NODE_ID;
        AreaTreeResponse areaTreeResponse = cache.get(cacheKey);
        if(areaTreeResponse != null){
            return areaTreeResponse;
        }
        // 递归生成
        areaTreeResponse = newAreaTreeByRecur(areaId);
        // 加入缓存，并设置超时时间
        cache.set(cacheKey, areaTreeResponse, BasicConst.Cache.AREA_CACHE_TTL);
        return areaTreeResponse;
    }
    /**
     * 根据父节点构造返回子树
     *
     * @param parentId
     * @return
     */
    private AreaTreeResponse newAreaTreeByRecur(Long parentId){
        // 初始化返回结果
        AreaTreeResponse areaTree = new AreaTreeResponse();
        // 获取直接子节点
        List<AreaTree> areaChildList = areaClosureMapper.getAreaTree(parentId, 1);
        if(areaChildList == null || areaChildList.size() == 0){
            return areaTree;
        } else {
            // 初始化当前节点的id和name
            Long curNodeId = null;
            String curNodeName = null;
            // 初始化当前节点对应的childList
            List<AreaTreeResponse> childList = new ArrayList<>();
            for (AreaTree areaChildNode : areaChildList) {
                curNodeId = areaChildNode.getParentId();
                curNodeName = areaChildNode.getParentName();
                // 递归，将子节点当成父节点向下递归
                AreaTreeResponse child = newAreaTreeByRecur(areaChildNode.getChildrenId());
                // 叶子节点设置child
                child.setAreaId(areaChildNode.getChildrenId());
                child.setAreaName(areaChildNode.getChildrenName());
                childList.add(child);
            }
            // 将childList传给上一节点
            areaTree.setAreaId(curNodeId);
            areaTree.setAreaName(curNodeName);
            areaTree.setChildren(childList);
            return areaTree;
        }
    }

写一个测试用例进行测试

@Test
public void getCurrentNodeTree(){
    AreaTreeResponse areaTreeResponse = areaService.getAreaTree(1L);
    // 模拟返回树
    String jsonObject = JSONObject.toJSONString(areaTreeResponse);
    System.out.println("lingyejun test result :"+jsonObject);
}

递归生成的树状Json如下

{
    "areaId":1,
    "areaName":"根节点",
    "children":[
        {
            "areaId":31,
            "areaName":"欧洲"
        },
        {
            "areaId":30,
            "areaName":"美洲"
        },
        {
            "areaId":29,
            "areaName":"亚洲",
            "children":[
                {
                    "areaId":35,
                    "areaName":"中国",
                    "children":[
                        {
                            "areaId":38,
                            "areaName":"广东省",
                            "children":[
                                {
                                    "areaId":41,
                                    "areaName":"深圳市"
                                },
                                {
                                    "areaId":42,
                                    "areaName":"广州市"
                                },
                                {
                                    "areaId":43,
                                    "areaName":"佛山市"
                                }
                            ]
                        },
                        {
                            "areaId":39,
                            "areaName":"新疆省"
                        },
                        {
                            "areaId":40,
                            "areaName":"广西省"
                        }
                    ]
                },
                {
                    "areaId":36,
                    "areaName":"日本"
                },
                {
                    "areaId":37,
                    "areaName":"朝鲜"
                }
            ]
        }
    ]
}

参考文章：https://www.biaodianfu.com/closure-table.html