Mongodb aggregate $facet

Question

我试图使用聚合管道的$facet阶段来匹配和分组文档，但我怀疑我的语法不正确。

有人能告诉我这个怎么了吗？继续获取消息"；流水线阶段规范对象必须包含恰好一个字段"；。

[
{
'$match': {
'Id': 59
}
}, {
'$unwind': {
'path': '$Vehicles'
}
}, {
// It's this stage that's playing up.
'$facet': {
'Offers': [
{
'$match': { 'Vehicles.VehicleGrouping': 'OOTW' }, 
'$group': {
'_id': '$Vehicles.Manufacturer', 
'count': { '$sum': 1 }
}
}
]
}
// End of problematic stage.
}
]

谢谢。

Answer 1

您已经将$match和$group放在一个对象中，请尝试以下操作：

db.collection.aggregate([
{
"$match": {
"Id": 59
}
},
{
"$unwind": {
"path": "$Vehicles"
}
},
{
// It's this stage that's playing up.
"$facet": {
"Offers": [
{
"$match": {
"Vehicles.VehicleGrouping": "OOTW"
}
},
{
"$group": {
"_id": "$Vehicles.Manufacturer",
"count": {
"$sum": 1
}
}
}
]
}  
}
])