• 【API要返回一棵树的结构】数据库表结构是平铺的数据，但是api要实现树状结构展示。api实现一棵树的结构，如何实现呢，递归？如何递归呢

    数据库中的数据是平铺的，一行行的，但是api要查询出来的数据要求是一棵树的结构，

    怎么把平铺的数据转换成树状结构呢？

    1.  
    2.     public List findCarbonRepo(Integer type){
    3.         // 1. 先查出所有数据。 baseFindList 方法就是查询数据库，返回一个list对象、CarbonRepo 就是数据库中某张表的数据实体
    4.  
    5.         List list = this.baseFindList(new CarbonRepo().setType(type).setActiveFlag(true));
    6.  
    7.         List collect = list.stream()
    8.                 // 2. 找出所有顶级（规定 2位code 为顶级）
    9.                 .filter(o -> o.getCode().length() == 2)
    10.                 // 3.给当前父级的 childList 设置子
    11.                 .peek(o -> {
    12.                     o.setChildList(getChildList(o, list));
    13.                     o.setKey(o.getId());
    14.                 })
    15.                 // 4.收集
    16.                 .collect(Collectors.toList());
    17.  
    18.         return  collect;
    19.     }
    1.  
    2.     // 通过递归的方式设置每个对象下的子属性。数据库中表的设计是通过code，parent
    3.     // 根据当前父类 找出子类， 并通过递归找出子类的子类
    4.     private List getChildList(CarbonRepo carbonRepo, List list) {
    5.         return list.stream()
    6.                 //筛选出父节点code == parentCode 的所有对象 => list
    7.                 .filter(o -> StringUtil.equals(carbonRepo.getCode(), o.getParentCode()))
    8.                 .peek(o -> {
    9.                     o.setChildList(getChildList(o, list));
    10.                     o.setKey(o.getId());
    11.                 })
    12.                 .collect(Collectors.toList());
    13.     }

    数据表结构：

    1. CREATE TABLE `data_carbon_repo` (
    2.   `id` int(11) NOT NULL AUTO_INCREMENT COMMENT 'id',
    3.   `code` varchar(32) NOT NULL COMMENT '编码',
    4.   `name` varchar(32) NOT NULL COMMENT '名称',
    5.   `parent_code` varchar(32) NOT NULL COMMENT '父编码',
    6.   `type` tinyint(4) NOT NULL DEFAULT '0' COMMENT '不同用途区分',
    7.   `active_flag` tinyint(4) NOT NULL DEFAULT '1' COMMENT '删除标识 1: 未删除 0:已删除',
    8.   `creator` bigint(20) DEFAULT NULL COMMENT '创建人id',
    9.   `modifier` bigint(20) DEFAULT NULL COMMENT '修改人id',
    10.   `create_time` datetime DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
    11.   `modify_time` datetime DEFAULT CURRENT_TIMESTAMP COMMENT '修改时间',
    12.   PRIMARY KEY (`id`)
    13. ) ENGINE=InnoDB AUTO_INCREMENT=344 DEFAULT CHARSET=utf8 COMMENT='材料库配置表'

    api返回的数据：

    1. {
    2.     "code": 100,
    3.     "message": "成功",
    4.     "data": [
    5.         {
    6.             "id": 279,
    7.             "code": "01",
    8.             "name": "国标数据",
    9.             "parentCode": "0",
    10.             "type": 2,
    11.             "activeFlag": 1,
    12.             "creator": null,
    13.             "modifier": null,
    14.             "createTime": "2023-08-18 16:40:46",
    15.             "modifyTime": "2023-08-18 16:40:46",
    16.             "childList": [
    17.                 {
    18.                     "id": 280,
    19.                     "code": "0101",
    20.                     "name": "材料碳排放计算标准",
    21.                     "parentCode": "01",
    22.                     "type": 2,
    23.                     "activeFlag": 1,
    24.                     "creator": null,
    25.                     "modifier": null,
    26.                     "createTime": "2023-08-18 16:40:46",
    27.                     "modifyTime": "2023-08-18 16:40:46",
    28.                     "childList": [
    29.                         {
    30.                             "id": 281,
    31.                             "code": "010101",
    32.                             "name": "水泥混凝土类",
    33.                             "parentCode": "0101",
    34.                             "type": 2,
    35.                             "activeFlag": 1,
    36.                             "creator": null,
    37.                             "modifier": null,
    38.                             "createTime": "2023-08-18 16:40:46",
    39.                             "modifyTime": "2023-08-18 16:40:46",
    40.                             "childList": [],
    41.                             "key": 281
    42.                         },
    43.                         {
    44.                             "id": 282,
    45.                             "code": "010102",
    46.                             "name": "建材制品类",
    47.                             "parentCode": "0101",
    48.                             "type": 2,
    49.                             "activeFlag": 1,
    50.                             "creator": null,
    51.                             "modifier": null,
    52.                             "createTime": "2023-08-18 16:40:46",
    53.                             "modifyTime": "2023-08-18 16:40:46",
    54.                             "childList": [],
    55.                             "key": 282
    56.                         },
    57.                         {
    58.                             "id": 283,
    59.                             "code": "010103",
    60.                             "name": "钢铁金属类",
    61.                             "parentCode": "0101",
    62.                             "type": 2,
    63.                             "activeFlag": 1,
    64.                             "creator": null,
    65.                             "modifier": null,
    66.                             "createTime": "2023-08-18 16:40:46",
    67.                             "modifyTime": "2023-08-18 16:40:46",
    68.                             "childList": [],
    69.                             "key": 283
    70.                         },
    71.                         {
    72.                             "id": 284,
    73.                             "code": "010104",
    74.                             "name": "玻璃及门窗类",
    75.                             "parentCode": "0101",
    76.                             "type": 2,
    77.                             "activeFlag": 1,
    78.                             "creator": null,
    79.                             "modifier": null,
    80.                             "createTime": "2023-08-18 16:40:46",
    81.                             "modifyTime": "2023-08-18 16:40:46",
    82.                             "childList": [],
    83.                             "key": 284
    84.                         },
    85.                         {
    86.                             "id": 285,
    87.                             "code": "010105",
    88.                             "name": "其他",
    89.                             "parentCode": "0101",
    90.                             "type": 2,
    91.                             "activeFlag": 1,
    92.                             "creator": null,
    93.                             "modifier": null,
    94.                             "createTime": "2023-08-18 16:40:46",
    95.                             "modifyTime": "2023-08-18 16:40:46",
    96.                             "childList": [],
    97.                             "key": 285
    98.                         }
    99.                     ],
    100.                     "key": 280
    101.                 }
    102.             ],
    103.             "key": 279
    104.         },
    105.         {
    106.             "id": 286,
    107.             "code": "02",
    108.             "name": "省标数据",
    109.             "parentCode": "0",
    110.             "type": 2,
    111.             "activeFlag": 1,
    112.             "creator": null,
    113.             "modifier": null,
    114.             "createTime": "2023-08-18 16:40:46",
    115.             "modifyTime": "2023-08-18 16:40:46",
    116.             "childList": [
    117.                 {
    118.                     "id": 287,
    119.                     "code": "0201",
    120.                     "name": "江苏省民用建筑碳排放规则（征求意见稿）",
    121.                     "parentCode": "02",
    122.                     "type": 2,
    123.                     "activeFlag": 1,
    124.                     "creator": null,
    125.                     "modifier": null,
    126.                     "createTime": "2023-08-18 16:40:46",
    127.                     "modifyTime": "2023-08-18 16:40:46",
    128.                     "childList": [
    129.                         {
    130.                             "id": 288,
    131.                             "code": "020101",
    132.                             "name": "水泥及其制品类",
    133.                             "parentCode": "0201",
    134.                             "type": 2,
    135.                             "activeFlag": 1,
    136.                             "creator": null,
    137.                             "modifier": null,
    138.                             "createTime": "2023-08-18 16:40:46",
    139.                             "modifyTime": "2023-08-18 16:40:46",
    140.                             "childList": [],
    141.                             "key": 288
    142.                         },
    143.                         {
    144.                             "id": 289,
    145.                             "code": "020102",
    146.                             "name": "地方材料及建材制品类",
    147.                             "parentCode": "0201",
    148.                             "type": 2,
    149.                             "activeFlag": 1,
    150.                             "creator": null,
    151.                             "modifier": null,
    152.                             "createTime": "2023-08-18 16:40:46",
    153.                             "modifyTime": "2023-08-18 16:40:46",
    154.                             "childList": [],
    155.                             "key": 289
    156.                         },
    157.                         {
    158.                             "id": 290,
    159.                             "code": "020103",
    160.                             "name": "黑色及有色金属类",
    161.                             "parentCode": "0201",
    162.                             "type": 2,
    163.                             "activeFlag": 1,
    164.                             "creator": null,
    165.                             "modifier": null,
    166.                             "createTime": "2023-08-18 16:40:46",
    167.                             "modifyTime": "2023-08-18 16:40:46",
    168.                             "childList": [],
    169.                             "key": 290
    170.                         },
    171.                         {
    172.                             "id": 291,
    173.                             "code": "020104",
    174.                             "name": "玻璃及门窗",
    175.                             "parentCode": "0201",
    176.                             "type": 2,
    177.                             "activeFlag": 1,
    178.                             "creator": null,
    179.                             "modifier": null,
    180.                             "createTime": "2023-08-18 16:40:46",
    181.                             "modifyTime": "2023-08-18 16:40:46",
    182.                             "childList": [],
    183.                             "key": 291
    184.                         },
    185.                         {
    186.                             "id": 292,
    187.                             "code": "020105",
    188.                             "name": "化学制品",
    189.                             "parentCode": "0201",
    190.                             "type": 2,
    191.                             "activeFlag": 1,
    192.                             "creator": null,
    193.                             "modifier": null,
    194.                             "createTime": "2023-08-18 16:40:46",
    195.                             "modifyTime": "2023-08-18 16:40:46",
    196.                             "childList": [],
    197.                             "key": 292
    198.                         },
    199.                         {
    200.                             "id": 293,
    201.                             "code": "020106",
    202.                             "name": "自来水",
    203.                             "parentCode": "0201",
    204.                             "type": 2,
    205.                             "activeFlag": 1,
    206.                             "creator": null,
    207.                             "modifier": null,
    208.                             "createTime": "2023-08-18 16:40:46",
    209.                             "modifyTime": "2023-08-18 16:40:46",
    210.                             "childList": [],
    211.                             "key": 293
    212.                         },
    213.                         {
    214.                             "id": 294,
    215.                             "code": "020107",
    216.                             "name": "装饰面层",
    217.                             "parentCode": "0201",
    218.                             "type": 2,
    219.                             "activeFlag": 1,
    220.                             "creator": null,
    221.                             "modifier": null,
    222.                             "createTime": "2023-08-18 16:40:46",
    223.                             "modifyTime": "2023-08-18 16:40:46",
    224.                             "childList": [],
    225.                             "key": 294
    226.                         },
    227.                         {
    228.                             "id": 295,
    229.                             "code": "020108",
    230.                             "name": "油漆、涂料类",
    231.                             "parentCode": "0201",
    232.                             "type": 2,
    233.                             "activeFlag": 1,
    234.                             "creator": null,
    235.                             "modifier": null,
    236.                             "createTime": "2023-08-18 16:40:46",
    237.                             "modifyTime": "2023-08-18 16:40:46",
    238.                             "childList": [],
    239.                             "key": 295
    240.                         },
    241.                         {
    242.                             "id": 296,
    243.                             "code": "020109",
    244.                             "name": "预制构件",
    245.                             "parentCode": "0201",
    246.                             "type": 2,
    247.                             "activeFlag": 1,
    248.                             "creator": null,
    249.                             "modifier": null,
    250.                             "createTime": "2023-08-18 16:40:46",
    251.                             "modifyTime": "2023-08-18 16:40:46",
    252.                             "childList": [],
    253.                             "key": 296
    254.                         },
    255.                         {
    256.                             "id": 297,
    257.                             "code": "020110",
    258.                             "name": "环保建材",
    259.                             "parentCode": "0201",
    260.                             "type": 2,
    261.                             "activeFlag": 1,
    262.                             "creator": null,
    263.                             "modifier": null,
    264.                             "createTime": "2023-08-18 16:40:46",
    265.                             "modifyTime": "2023-08-18 16:40:46",
    266.                             "childList": [],
    267.                             "key": 297
    268.                         }
    269.                     ],
    270.                     "key": 287
    271.                 }                 
    272.             ],
    273.             "key": 286
    274.         }         
    275.     ],
    276.     "success": true
    277. }

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  • 原文地址：https://blog.csdn.net/xzb5566/article/details/133673902