我有mongodb中的TblStudent
集合
{
"_id": ObjectId("5baa85041d7859f40d000029"),
"Name": "John Doe",
"RollNo": 12,
"Class": "Ist"
....
}
我有另一个集合TblRoute
喜欢
{
"_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。我使用下面的代码行
$query = ['_id' => new MongoDB\BSON\ObjectID($this->id)];
$cursor = $this->db->TblRoute->aggregate([
['$match' => $query],
[
'$lookup' =>
[
'from' => "TblStudent",
'let' => ['StudentId' => '$StudentDetails.StudentId'],
'pipeline' => [
[ '$match' =>
['$expr' =>
['$eq' => ['$StudentId', '$$StudentId' ] ]
]
],
[ '$project' => ['Name' => 1, 'RollNo' => 1 ] ]
],
'as' => "StudentDetails.StudentData"
]
]
]);
我一直在尝试从另一个集合中获取数据,但仅限于某些字段。我试图从TblRoute中的TblStudent获取学生名称和RollNo字段,以使文档阵列重量轻。通常,$ lookup阶段从另一个集合中获取所有字段。
我正在尝试上面的代码。它会抛出错误消息
"StudentDetails.StudentData" is coming empty 'StudentDetails' => MongoDB\Model\BSONDocument::__set_state(array( 'StudentData' => MongoDB\Model\BSONArray::__set_state(array( )), )),
但我认为代码编写不正确。实际方法可能有所不同。请帮我解决问题。
我希望输出类似于
{
"_id": ObjectId("5baa818d1d78594010000029"),
"Name": "New york City",
"StopDetails": [
.....
],
"StudentDetails": [
{
"StudentId": ObjectId("5baa85041d7859f40d000029"),
"VehicleId": "7756",
"StudentData": [
"Name": ..
"RollNo":...
]
},
{
"StudentId": ObjectId("5baa85f61d7859401000002a"),
"VehicleId": "7676",
"StudentData": [
"Name": ..
"RollNo":...
]
}
]
}
使用以下聚合。
来自文档的说明
用户变量名必须以小写的ascii字母[a-z]或非ascii字符开头。
因此,将$let
变量更改为studentid
,并修复代码中的其他问题。
db.TblRoute.aggregate([
{"$match":ObjectId("5baa818d1d78594010000029")},
{"$lookup":{
"from":"TblStudent",
"let":{"studentid":"$StudentDetails.StudentId"},
"pipeline":[
{"$match":{"$expr":{"$in":["$_id","$$studentid"]}}},
{"$project":{"Name":1,"RollNo":1}}
],
"as":"StudentDetails.StudentData"
}}
])