$unwind and $lookup with php mongodb

Question

我有一张桌子 TblStudent in mongodb 喜欢

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

我有另一个表 TblRoute 像

{
"_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!!

$query = ['_id' => new MongoDBBSONObjectID($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' ]
]]
]);

它抛出错误消息未捕获异常"MongoDB\驱动程序\异常\运行时异常"，消息"字段'学生详细信息.学生 ID'必须是累加器对象"

基本上，我想使用查找聚合从另一个表中获取数据。因此，经过在线帮助和进一步研究，我能够编写上面的代码。这里的主要问题是语句$unwind之前的代码将输出生成为单独的数组。如果我们在$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(的丢失。我要 保存它们。因此，经过研究，我尝试添加$group以将其放回StudentDetails嵌入式文档中。

期望的输出

{
"_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":...
]
}
]
}

请帮我解决问题

Answer 1

你可以做这样的事情

$cursor = $this->db->TblRoute->aggregate([
[ "$match" => $query ],
[ "$unwind": "$StudentDetails" ],
[ "$lookup" => [
"from" => "TblStudent",
"let" => [ "studentid" => "$StudentDetails.StudentId" ],
"pipeline" => [
[ "$match" => [ "$expr"=> [ "$eq" => [ "$_id", "$$studentid" ]]]],
[ "$project" => [ "Name"=> 1, "RollNo" => 1, "_id"=> 1 ]]
],
"as" => "StudentDetails.StudentId"
]],
[ "$unwind": "$StudentDetails.StudentId" ],
[ "$group"=> [
"_id"=> "$_id",
"Name": [ "$first"=> "$Name" ],
"StopDetails": [ "$first"=> "$StopDetails" ],
"StudentDetails"=> [ "$push"=> "$StudentDetails" ]
]]
])