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记一次mongodb聚合查询
来源：cnblogs　　作者：du_blog　　时间：2019/4/16 8:47:22　　对本文有异议

　　先说一下场景，产品中用到了简单的表单构造器，开始提供了一系列的控件，例如单行文本框、多行文本框、单选、复选、时间等，之后你可以拖拽控件自己组装你想要的表单……网上有很多的表单构造器，这里就不细说了，可能功能有多有少，但是原理类似。因为这种表单的这种实现方式，我们不单单要存储表单的真实数据，还要存储对应表单的配置数据来渲染表单的样子。这里不细说配置相关的事情，细说一下表单数据的存储和查询。

　　对于一条记录有很多共有属性：主键ID、创建用户ID、创建时间、表单ID（用于读取表单配置）等一些业务数据，这里着重说一下表单ID也就是下面演示中提到的TableCode,我们这种存储方式可以将业务上的多种表都存储在现在的一张表中，所以必须要一个字段来区分这条记录存储的具体是什么信息，以方便在查询时找到具体的数据；还有一些就是具体的表单项了。我们采用的是Mongodb存储，不用想肯定是复杂结构了，数组或者键值对对象……也不知道什么原因了，我们采用的是数组，这里记作FormItems，FormItems列中存储着所有的表单项，具体的看一下数据库的存储结构：

  1. {
  2.     "_id" : "1",
  3.     "CreateUserName" : "ddz1",
  4.     "CreateDate" : "2018-02-07",
  5.     "FormItems" : [ 
  6.         {
  7.             "key" : "CarBrand",
  8.             "value" : "红旗"
  9.         }, 
  10.         {
  11.             "key" : "VehicleType",
  12.             "value" : "H7"
  13.         }, 
  14.         {
  15.             "key" : "CarNum",
  16.             "value" : "京A00001"
  17.         }, 
  18.         {
  19.             "key" : "PurchaseDate",
  20.             "value" : "2019-01-01"
  21.         }
  22.     ],
  23.     "TableCode" : "CarInfo" 
  24. }

　　上面看到是一个缩减版的结构（为了方便演示），简单的介绍一下：TableCode-表单名称，FormItems数组中存储着所有的表单项，key本来是唯一值，这里仅仅为了演示所以如此，value就是具体的表单项的值了。查询演示用到了三张表，第一张表如上，车辆信息表：车牌子、车型、牌照、购买日期等；车辆维修表：车辆ID、花费、内容；出车记录表：车辆ID、收入、里程、备注。首先插入一些数据：

  1. try{
  2.     db.t1.insertMany([{
  3.         "_id": "1",
  4.         "CreateUserName": "ddz1",
  5.         "CreateDate": "2018-02-07",
  6.         "FormItems": [{
  7.             "key": "CarBrand",
  8.             "value": "红旗"
  9.         },
  10.         {
  11.             "key": "VehicleType",
  12.             "value": "H7"
  13.         },
  14.         {
  15.             "key": "CarNum",
  16.             "value": "京A00001"
  17.         },
  18.         {
  19.             "key": "PurchaseDate",
  20.             "value": "2019-01-01"
  21.         }],
  22.         "TableCode": "CarInfo"
  23.     },{
  24.         "_id": "2",
  25.         "CreateUserName": "ddz1",
  26.         "CreateDate": "2018-02-08",
  27.         "FormItems": [{
  28.             "key": "CarBrand",
  29.             "value": "红旗"
  30.         },
  31.         {
  32.             "key": "VehicleType",
  33.             "value": "H5"
  34.         },
  35.         {
  36.             "key": "CarNum",
  37.             "value": "京A00002"
  38.         },
  39.         {
  40.             "key": "PurchaseDate",
  41.             "value": "2019-02-01"
  42.         }],
  43.         "TableCode": "CarInfo"
  44.     },{
  45.         "_id": "3",
  46.         "CreateUserName": "ddz1",
  47.         "CreateDate": "2018-02-09",
  48.         "FormItems": [{
  49.             "key": "CarBrand",
  50.             "value": "红旗"
  51.         },
  52.         {
  53.             "key": "VehicleType",
  54.             "value": "L5"
  55.         },
  56.         {
  57.             "key": "CarNum",
  58.             "value": "京A00003"
  59.         },
  60.         {
  61.             "key": "PurchaseDate",
  62.             "value": "2019-03-01"
  63.         }],
  64.         "TableCode": "CarInfo"
  65.     },
  66.     {
  67.         "_id": "4",
  68.         "CreateUserName": "ddz1",
  69.         "CreateDate": "2018-02-10",
  70.         "FormItems": [{
  71.             "key": "CarBrand",
  72.             "value": "长城"
  73.         },
  74.         {
  75.             "key": "VehicleType",
  76.             "value": "哈弗H6"
  77.         },
  78.         {
  79.             "key": "CarNum",
  80.             "value": "京A00004"
  81.         },
  82.         {
  83.             "key": "PurchaseDate",
  84.             "value": "2018-03-01"
  85.         }],
  86.         "TableCode": "CarInfo"
  87.     },{
  88.         "_id": "5",
  89.         "CreateUserName": "ddz1",
  90.         "CreateDate": "2018-02-09",
  91.         "FormItems": [{
  92.             "key": "CarBrand",
  93.             "value": "长城"
  94.         },
  95.         {
  96.             "key": "VehicleType",
  97.             "value": "哈弗H5"
  98.         },
  99.         {
  100.             "key": "CarNum",
  101.             "value": "京A00005"
  102.         },
  103.         {
  104.             "key": "PurchaseDate",
  105.             "value": "2018-03-01"
  106.         }],
  107.         "TableCode": "CarInfo"
  108.     },{
  109.         "_id": "6",
  110.         "CreateUserName": "ddz1",
  111.         "CreateDate": "2018-03-09",
  112.         "FormItems": [{
  113.             "key": "CarBrand",
  114.             "value": "长城"
  115.         },
  116.         {
  117.             "key": "VehicleType",
  118.             "value": "哈弗H4"
  119.         },
  120.         {
  121.             "key": "CarNum",
  122.             "value": "京A00006"
  123.         },
  124.         {
  125.             "key": "PurchaseDate",
  126.             "value": "2018-03-01"
  127.         }],
  128.         "TableCode": "CarInfo"
  129.     },{
  130.         "_id": "7",
  131.         "CreateUserName": "ddz100",
  132.         "CreateDate": "2018-06-06",
  133.         "FormItems": [{
  134.             "key": "CarId",
  135.             "value": "1"
  136.         },
  137.         {
  138.             "key": "Cost",
  139.             "value": 100
  140.         },
  141.         {
  142.             "key": "Contents",
  143.             "value": "喷漆"
  144.         }],
  145.         "TableCode": "MaintenanceRecord"
  146.     },{
  147.         "_id": "8",
  148.         "CreateUserName": "ddz100",
  149.         "CreateDate": "2018-08-06",
  150.         "FormItems": [{
  151.             "key": "CarId",
  152.             "value": "1"
  153.         },
  154.         {
  155.             "key": "Cost",
  156.             "value": 25
  157.         },
  158.         {
  159.             "key": "Contents",
  160.             "value": "洗车"
  161.         }],
  162.         "TableCode": "MaintenanceRecord"
  163.     },{
  164.         "_id": "9",
  165.         "CreateUserName": "ddz101",
  166.         "CreateDate": "2018-06-03",
  167.         "FormItems": [{
  168.             "key": "CarId",
  169.             "value": "2"
  170.         },
  171.         {
  172.             "key": "Cost",
  173.             "value": 1560
  174.         },
  175.         {
  176.             "key": "Contents",
  177.             "value": "换轮胎"
  178.         }],
  179.         "TableCode": "MaintenanceRecord"
  180.     },{
  181.         "_id": "10",
  182.         "CreateUserName": "ddz102",
  183.         "CreateDate": "2018-06-26",
  184.         "FormItems": [{
  185.             "key": "CarId",
  186.             "value": "3"
  187.         },
  188.         {
  189.             "key": "Cost",
  190.             "value": 36
  191.         },
  192.         {
  193.             "key": "Contents",
  194.             "value": "爆胎"
  195.         }],
  196.         "TableCode": "MaintenanceRecord"
  197.     },{
  198.         "_id": "11",
  199.         "CreateUserName": "ddz103",
  200.         "CreateDate": "2018-09-08",
  201.         "FormItems": [{
  202.             "key": "CarId",
  203.             "value": "3"
  204.         },
  205.         {
  206.             "key": "Cost",
  207.             "value": 1630
  208.         },
  209.         {
  210.             "key": "Contents",
  211.             "value": "换加速器"
  212.         }],
  213.         "TableCode": "MaintenanceRecord"
  214.     },{
  215.         "_id": "12",
  216.         "CreateUserName": "ddz10",
  217.         "CreateDate": "2018-06-06",
  218.         "FormItems": [{
  219.             "key": "CarId",
  220.             "value": "1"
  221.         },
  222.         {
  223.             "key": "Income",
  224.             "value": 106
  225.         },
  226.         {
  227.             "key": "Mileage",
  228.             "value": 50
  229.         },
  230.         {
  231.             "key": "Remarks",
  232.             "value": "123"
  233.         }],
  234.         "TableCode": "DispatchRecord"
  235.     },{
  236.         "_id": "13",
  237.         "CreateUserName": "ddz11",
  238.         "CreateDate": "2018-06-16",
  239.         "FormItems": [{
  240.             "key": "CarId",
  241.             "value": "1"
  242.         },
  243.         {
  244.             "key": "Income",
  245.             "value": 250
  246.         },
  247.         {
  248.             "key": "Mileage",
  249.             "value": 100
  250.         },
  251.         {
  252.             "key": "Remarks",
  253.             "value": "123"
  254.         }],
  255.         "TableCode": "DispatchRecord"
  256.     },{
  257.         "_id": "14",
  258.         "CreateUserName": "ddz12",
  259.         "CreateDate": "2018-06-16",
  260.         "FormItems": [{
  261.             "key": "CarId",
  262.             "value": "2"
  263.         },
  264.         {
  265.             "key": "Income",
  266.             "value": 1000
  267.         },
  268.         {
  269.             "key": "Mileage",
  270.             "value": 630
  271.         },
  272.         {
  273.             "key": "Remarks",
  274.             "value": "2345sfgfg"
  275.         }],
  276.         "TableCode": "DispatchRecord"
  277.     },{
  278.         "_id": "15",
  279.         "CreateUserName": "ddz12",
  280.         "CreateDate": "2018-08-16",
  281.         "FormItems": [{
  282.             "key": "CarId",
  283.             "value": "3"
  284.         },
  285.         {
  286.             "key": "Income",
  287.             "value": 1213
  288.         },
  289.         {
  290.             "key": "Mileage",
  291.             "value": 569
  292.         },
  293.         {
  294.             "key": "Remarks",
  295.             "value": "12asdfasdfasdf3"
  296.         }],
  297.         "TableCode": "DispatchRecord"
  298.     }]);
  299. }catch(e){
  300.     print(e);
  301. }
View Code

　　这种存储方式有一定的好处，但是弊端也很明显：查询、排序等很费劲，如果服务器端以这样的方式返回客户端，客户端还得解析FormItems，非常不友好（感觉自己在给自己找麻烦）……所以我就想看看能不能在所有的查询操作之前，首先处理一下数据，将FormItems中的表单项都提到文档的最外层和公共字段一个层次，之后在进行查询排序似乎就简单点了，为了实现这个目标真是废了九牛二虎之力，道路相当坎坷，经历的时间也很长，不过最终好在找到一个例子解决了我们的问题：https://jira.mongodb.org/browse/SERVER-5947 。在此表示感谢，非常感谢……在这之后又遇到了一个问题就是：在关联查询时mongodb的处理方式是将所有的相关联的数据存储在一个属性中，因为我们所有的“表”都存在这一个表中，所以关联的也是这一张表，也就是关联自己查询，结果得到关联的数据还是没有处理之前的样子，相同的数据最后的结构都不一样，都不好意思返回客户端，这个问题比之前的问题更费劲……不知道度过了多少天，我的一个同事说弄出来了，我就有点……所以我也想尝试一下，最后废了半天劲儿终于弄出来，不知道和同事弄的一样不一样，这里只能吐槽mongodb你怎么能这样……看一下代码：

  1. db.getCollection('t1').aggregate([
  2.     {$addFields:
  3.         {
  4.             FormValueObj:{
  5.                 $arrayToObject:{
  6.                     $map:
  7.                      {
  8.                        input: "$FormItems",
  9.                        as: "field",
  10.                        in: ["$$field.key","$$field.value"]
  11.                      }
  12.                 }
  13.             }
  14.         }
  15.     },
  16.     {
  17.         $addFields:{
  18.             "FormValueObj._id":"$_id",
  19.             "FormValueObj.CreateUserName":"$CreateUserName",
  20.             "FormValueObj.CreateDate":"$CreateDate",
  21.             "FormValueObj.TableCode":"$TableCode"
  22.         }
  23.     },
  24.     {
  25.         $replaceRoot: { newRoot: "$FormValueObj" }
  26.     },
  27.     {
  28.         $lookup:{
  29.            from: "t1",
  30.            localField: "_id",
  31.            foreignField: "FormItems.value",
  32.            as: "RelationData1"
  33.         }
  34.     },
  35.     {
  36.         $addFields:{
  37.             RelationData1:{
  38.                  $map:
  39.                  {
  40.                     input: "$RelationData1",
  41.                     as: "tr",
  42.                     in: {
  43.                         $arrayToObject:{
  44.                             $map:
  45.                              {
  46.                                input:{ 
  47.                                    $concatArrays: [ 
  48.                                    [
  49.                                         {key:"_id",value:"$$tr._id"},
  50.                                         {key:"CreateUserName",value:"$$tr.CreateUserName"},
  51.                                         {key:"CreateDate",value:"$$tr.CreateDate"},
  52.                                         {key:"TableCode",value:"$$tr.TableCode"},
  53.                                    ], 
  54.                                    "$$tr.FormItems" ] 
  55.                                },
  56.                                as: "field",
  57.                                in: ["$$field.key","$$field.value"]
  58.                              }
  59.                         }
  60.                     }
  61.                  }
  62.             }
  63.         }
  64.     }
  65. ])
查询语句
  1. /* 1 */
  2. {
  3.     "CarBrand" : "红旗",
  4.     "VehicleType" : "H7",
  5.     "CarNum" : "京A00001",
  6.     "PurchaseDate" : "2019-01-01",
  7.     "_id" : "1",
  8.     "CreateUserName" : "ddz1",
  9.     "CreateDate" : "2018-02-07",
  10.     "TableCode" : "CarInfo",
  11.     "RelationData1" : [ 
  12.         {
  13.             "_id" : "7",
  14.             "CreateUserName" : "ddz100",
  15.             "CreateDate" : "2018-06-06",
  16.             "TableCode" : "MaintenanceRecord",
  17.             "CarId" : "1",
  18.             "Cost" : 100.0,
  19.             "Contents" : "喷漆"
  20.         }, 
  21.         {
  22.             "_id" : "8",
  23.             "CreateUserName" : "ddz100",
  24.             "CreateDate" : "2018-08-06",
  25.             "TableCode" : "MaintenanceRecord",
  26.             "CarId" : "1",
  27.             "Cost" : 25.0,
  28.             "Contents" : "洗车"
  29.         }, 
  30.         {
  31.             "_id" : "12",
  32.             "CreateUserName" : "ddz10",
  33.             "CreateDate" : "2018-06-06",
  34.             "TableCode" : "DispatchRecord",
  35.             "CarId" : "1",
  36.             "Income" : 106.0,
  37.             "Mileage" : 50.0,
  38.             "Remarks" : "123"
  39.         }, 
  40.         {
  41.             "_id" : "13",
  42.             "CreateUserName" : "ddz11",
  43.             "CreateDate" : "2018-06-16",
  44.             "TableCode" : "DispatchRecord",
  45.             "CarId" : "1",
  46.             "Income" : 250.0,
  47.             "Mileage" : 100.0,
  48.             "Remarks" : "123"
  49.         }
  50.     ]
  51. }
  53. /* 2 */
  54. {
  55.     "CarBrand" : "红旗",
  56.     "VehicleType" : "H5",
  57.     "CarNum" : "京A00002",
  58.     "PurchaseDate" : "2019-02-01",
  59.     "_id" : "2",
  60.     "CreateUserName" : "ddz1",
  61.     "CreateDate" : "2018-02-08",
  62.     "TableCode" : "CarInfo",
  63.     "RelationData1" : [ 
  64.         {
  65.             "_id" : "9",
  66.             "CreateUserName" : "ddz101",
  67.             "CreateDate" : "2018-06-03",
  68.             "TableCode" : "MaintenanceRecord",
  69.             "CarId" : "2",
  70.             "Cost" : 1560.0,
  71.             "Contents" : "换轮胎"
  72.         }, 
  73.         {
  74.             "_id" : "14",
  75.             "CreateUserName" : "ddz12",
  76.             "CreateDate" : "2018-06-16",
  77.             "TableCode" : "DispatchRecord",
  78.             "CarId" : "2",
  79.             "Income" : 1000.0,
  80.             "Mileage" : 630.0,
  81.             "Remarks" : "2345sfgfg"
  82.         }
  83.     ]
  84. }
  86. /* 3 */
  87. {
  88.     "CarBrand" : "红旗",
  89.     "VehicleType" : "L5",
  90.     "CarNum" : "京A00003",
  91.     "PurchaseDate" : "2019-03-01",
  92.     "_id" : "3",
  93.     "CreateUserName" : "ddz1",
  94.     "CreateDate" : "2018-02-09",
  95.     "TableCode" : "CarInfo",
  96.     "RelationData1" : [ 
  97.         {
  98.             "_id" : "10",
  99.             "CreateUserName" : "ddz102",
  100.             "CreateDate" : "2018-06-26",
  101.             "TableCode" : "MaintenanceRecord",
  102.             "CarId" : "3",
  103.             "Cost" : 36.0,
  104.             "Contents" : "爆胎"
  105.         }, 
  106.         {
  107.             "_id" : "11",
  108.             "CreateUserName" : "ddz103",
  109.             "CreateDate" : "2018-09-08",
  110.             "TableCode" : "MaintenanceRecord",
  111.             "CarId" : "3",
  112.             "Cost" : 1630.0,
  113.             "Contents" : "换加速器"
  114.         }, 
  115.         {
  116.             "_id" : "15",
  117.             "CreateUserName" : "ddz12",
  118.             "CreateDate" : "2018-08-16",
  119.             "TableCode" : "DispatchRecord",
  120.             "CarId" : "3",
  121.             "Income" : 1213.0,
  122.             "Mileage" : 569.0,
  123.             "Remarks" : "12asdfasdfasdf3"
  124.         }
  125.     ]
  126. }
  128. /* 4 */
  129. {
  130.     "CarBrand" : "长城",
  131.     "VehicleType" : "哈弗H6",
  132.     "CarNum" : "京A00004",
  133.     "PurchaseDate" : "2018-03-01",
  134.     "_id" : "4",
  135.     "CreateUserName" : "ddz1",
  136.     "CreateDate" : "2018-02-10",
  137.     "TableCode" : "CarInfo",
  138.     "RelationData1" : []
  139. }
  141. /* 5 */
  142. {
  143.     "CarBrand" : "长城",
  144.     "VehicleType" : "哈弗H5",
  145.     "CarNum" : "京A00005",
  146.     "PurchaseDate" : "2018-03-01",
  147.     "_id" : "5",
  148.     "CreateUserName" : "ddz1",
  149.     "CreateDate" : "2018-02-09",
  150.     "TableCode" : "CarInfo",
  151.     "RelationData1" : []
  152. }
  154. /* 6 */
  155. {
  156.     "CarBrand" : "长城",
  157.     "VehicleType" : "哈弗H4",
  158.     "CarNum" : "京A00006",
  159.     "PurchaseDate" : "2018-03-01",
  160.     "_id" : "6",
  161.     "CreateUserName" : "ddz1",
  162.     "CreateDate" : "2018-03-09",
  163.     "TableCode" : "CarInfo",
  164.     "RelationData1" : []
  165. }
  167. /* 7 */
  168. {
  169.     "CarId" : "1",
  170.     "Cost" : 100.0,
  171.     "Contents" : "喷漆",
  172.     "_id" : "7",
  173.     "CreateUserName" : "ddz100",
  174.     "CreateDate" : "2018-06-06",
  175.     "TableCode" : "MaintenanceRecord",
  176.     "RelationData1" : []
  177. }
  179. /* 8 */
  180. {
  181.     "CarId" : "1",
  182.     "Cost" : 25.0,
  183.     "Contents" : "洗车",
  184.     "_id" : "8",
  185.     "CreateUserName" : "ddz100",
  186.     "CreateDate" : "2018-08-06",
  187.     "TableCode" : "MaintenanceRecord",
  188.     "RelationData1" : []
  189. }
  191. /* 9 */
  192. {
  193.     "CarId" : "2",
  194.     "Cost" : 1560.0,
  195.     "Contents" : "换轮胎",
  196.     "_id" : "9",
  197.     "CreateUserName" : "ddz101",
  198.     "CreateDate" : "2018-06-03",
  199.     "TableCode" : "MaintenanceRecord",
  200.     "RelationData1" : []
  201. }
  203. /* 10 */
  204. {
  205.     "CarId" : "3",
  206.     "Cost" : 36.0,
  207.     "Contents" : "爆胎",
  208.     "_id" : "10",
  209.     "CreateUserName" : "ddz102",
  210.     "CreateDate" : "2018-06-26",
  211.     "TableCode" : "MaintenanceRecord",
  212.     "RelationData1" : []
  213. }
  215. /* 11 */
  216. {
  217.     "CarId" : "3",
  218.     "Cost" : 1630.0,
  219.     "Contents" : "换加速器",
  220.     "_id" : "11",
  221.     "CreateUserName" : "ddz103",
  222.     "CreateDate" : "2018-09-08",
  223.     "TableCode" : "MaintenanceRecord",
  224.     "RelationData1" : []
  225. }
  227. /* 12 */
  228. {
  229.     "CarId" : "1",
  230.     "Income" : 106.0,
  231.     "Mileage" : 50.0,
  232.     "Remarks" : "123",
  233.     "_id" : "12",
  234.     "CreateUserName" : "ddz10",
  235.     "CreateDate" : "2018-06-06",
  236.     "TableCode" : "DispatchRecord",
  237.     "RelationData1" : []
  238. }
  240. /* 13 */
  241. {
  242.     "CarId" : "1",
  243.     "Income" : 250.0,
  244.     "Mileage" : 100.0,
  245.     "Remarks" : "123",
  246.     "_id" : "13",
  247.     "CreateUserName" : "ddz11",
  248.     "CreateDate" : "2018-06-16",
  249.     "TableCode" : "DispatchRecord",
  250.     "RelationData1" : []
  251. }
  253. /* 14 */
  254. {
  255.     "CarId" : "2",
  256.     "Income" : 1000.0,
  257.     "Mileage" : 630.0,
  258.     "Remarks" : "2345sfgfg",
  259.     "_id" : "14",
  260.     "CreateUserName" : "ddz12",
  261.     "CreateDate" : "2018-06-16",
  262.     "TableCode" : "DispatchRecord",
  263.     "RelationData1" : []
  264. }
  266. /* 15 */
  267. {
  268.     "CarId" : "3",
  269.     "Income" : 1213.0,
  270.     "Mileage" : 569.0,
  271.     "Remarks" : "12asdfasdfasdf3",
  272.     "_id" : "15",
  273.     "CreateUserName" : "ddz12",
  274.     "CreateDate" : "2018-08-16",
  275.     "TableCode" : "DispatchRecord",
  276.     "RelationData1" : []
  277. }
查询结果

　　你可能看到了查询语句太长了，这还是最基本的，幸好3.4之后提供了视图的功能，我们可以创建一个视图，弄成我们想要的样子：

  1. db.createView("t1view","t1",[
  2.     {$addFields:
  3.         {
  4.             FormValueObj:{
  5.                 $arrayToObject:{
  6.                     $map:
  7.                      {
  8.                        input: "$FormItems",
  9.                        as: "field",
  10.                        in: ["$$field.key","$$field.value"]
  11.                      }
  12.                 }
  13.             }
  14.         }
  15.     },
  16.     {
  17.         $addFields:{
  18.             "FormValueObj._id":"$_id",
  19.             "FormValueObj.CreateUserName":"$CreateUserName",
  20.             "FormValueObj.CreateDate":"$CreateDate",
  21.             "FormValueObj.TableCode":"$TableCode"
  22.         }
  23.     },
  24.     {
  25.         $replaceRoot: { newRoot: "$FormValueObj" }
  26.     }
  27. ])
创建视图

　　之后我们就是在视图中查询了

  1. db.getCollection('t1view').aggregate([
  2.     {$match:{_id:"1"}},
  3.     {
  4.         $lookup:{
  5.            from: "t1view",
  6.            localField: "_id",
  7.            foreignField: "CarId",
  8.            as: "RelationData1"
  9.         }
  10.     }
  11. ])
视图查询
  1. /* 1 */
  2. {
  3.     "CarBrand" : "红旗",
  4.     "VehicleType" : "H7",
  5.     "CarNum" : "京A00001",
  6.     "PurchaseDate" : "2019-01-01",
  7.     "_id" : "1",
  8.     "CreateUserName" : "ddz1",
  9.     "CreateDate" : "2018-02-07",
  10.     "TableCode" : "CarInfo",
  11.     "RelationData1" : [ 
  12.         {
  13.             "CarId" : "1",
  14.             "Cost" : 100.0,
  15.             "Contents" : "喷漆",
  16.             "_id" : "7",
  17.             "CreateUserName" : "ddz100",
  18.             "CreateDate" : "2018-06-06",
  19.             "TableCode" : "MaintenanceRecord"
  20.         }, 
  21.         {
  22.             "CarId" : "1",
  23.             "Cost" : 25.0,
  24.             "Contents" : "洗车",
  25.             "_id" : "8",
  26.             "CreateUserName" : "ddz100",
  27.             "CreateDate" : "2018-08-06",
  28.             "TableCode" : "MaintenanceRecord"
  29.         }, 
  30.         {
  31.             "CarId" : "1",
  32.             "Income" : 106.0,
  33.             "Mileage" : 50.0,
  34.             "Remarks" : "123",
  35.             "_id" : "12",
  36.             "CreateUserName" : "ddz10",
  37.             "CreateDate" : "2018-06-06",
  38.             "TableCode" : "DispatchRecord"
  39.         }, 
  40.         {
  41.             "CarId" : "1",
  42.             "Income" : 250.0,
  43.             "Mileage" : 100.0,
  44.             "Remarks" : "123",
  45.             "_id" : "13",
  46.             "CreateUserName" : "ddz11",
  47.             "CreateDate" : "2018-06-16",
  48.             "TableCode" : "DispatchRecord"
  49.         }
  50.     ]
  51. }
视图查询结果

　　这样在操作就简单多了，还避免了上面的第二个问题,??????，不知道你有没有发现一个问题，在上面的查询结果中“RelationData1”中冗余了车辆维护表和车辆出车记录的所有相关记录，这不是我们想要的，我们想要的是RelationData1是相关的“车辆维护记录”，RelationData2是相关的“车辆出车记录”，出现这种问题的原因是关联查询时，关联的表不允许过滤，3.4版本之前就这样了，不知道大神们有没有好的办法，我只能用升级来解决了，3.6之后就可以了……

　　暂时就记到这里吧！有时间在补充。

原文链接：http://www.cnblogs.com/du-blog/p/10713312.html

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