Question

我在mongodb中有一个表TblStudent，如

       {
      "_id": ObjectId("5baa85041d7859f40d000029"),
       "Name": "John Doe",
       "RollNo": 12,
       "Class": "Ist"
        ....
       }

我还有另一个表TblRoute之类的

   {
   "_id": ObjectId("5baa818d1d78594010000029"),
   "Name": "New york City",
   "StopDetails": [
   {
    "StopId": "abc777",
    "Name": "Block no 3"
   },
   {
   "StopId": "abc888",
   "Name": "Block no 4"
   }
 ],
"NumberOfSeats": "10",
"StudentDetails": [
 {
   "StudentId": ObjectId("5baa85041d7859f40d000029"),
   "VehicleId": "7756"
  },
  {
   "StudentId": ObjectId("5baa85f61d7859401000002a"),
   "VehicleId": "7676"
 }
 ]
}

我正在使用mongodb 3.6平台。获得在线帮助后，我正在使用以下代码行！！！

      $query = ['_id' => new MongoDB\BSON\ObjectID($this->id)];
      $cursor = $this->db->TblRoute->aggregate([
      ['$match' => $query],
      ['$lookup' => [
         'from' => "TblStudent",
         'let' => ['studentid' => '$StudentDetails.StudentId'],
         'pipeline' => [
         ['$match' => ['$expr'=> ['$in' => ['$_id','$$studentid' ]]]],
         ['$project' => ['Name'=> 1,'RollNo' => 1, '_id'=> 1]]
         ],
         'as' => 'studentObjects',
       ]],
       ['$unwind'=> '$studentObjects' ],
        // Group back to arrays
       [ '$group'=> [
               'StudentDetails.StudentId'=> '$_id',
                'StudentDetails.StudentData'=> [ '$push'=> '$studentObjects' ]
       ]]

     ]);

它抛出错误消息，消息为“ StudentDetails.StudentId”字段必须是累加器对象”，未捕获的异常“ MongoDB \ Driver \ Exception \ RuntimeException”

基本上，我想使用查找聚合从另一个表中获取数据。因此，在获得在线帮助和进一步研究之后，我能够编写以上代码。这里的主要问题是$ unwind语句之前的代码将输出生成为单独的数组。如果我们在$ lookup中写'as'=>'StudentDetails.studentObjects'，则数据将被新数据覆盖，从而导致其他字段（如Vehicleid等）丢失。保存它们。因此，在研究之后，我尝试添加$ group将其放回StudentDetails嵌入式文档中。

所需的输出

        {
"_id": ObjectId("5baa818d1d78594010000029"),
"Name": "New york City",
"StopDetails": [
     .....
  ],
   "StudentDetails": [
   {
   "StudentId": ObjectId("5baa85041d7859f40d000029"),
   "VehicleId": "7756",
   "StudentData": [
      "Name": ..
      "RollNo":...
    ]
    },
    {
    "StudentId": ObjectId("5baa85f61d7859401000002a"),
    "VehicleId": "7676",
     "StudentData": [
      "Name": ..
      "RollNo":...
    ]
   }
   ]
  }

请帮助我解决问题

Answer 1

您可以执行以下操作

myop

$ unwind和$ lookup与php mongodb

1 个答案: