MongoDB 聚合与 $lookup 限制某些字段从查询返回
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MongoDB aggregation with $lookup limit some fields to return from query
提问by Samuel Rondeau-Millaire
In mongo, after doing an aggregationwith $lookup, I would like the request to return only some fields and not the whole document.
在 mongo 中，在执行aggregationwith 之后$lookup，我希望请求仅返回某些字段而不是整个文档。
I have the following query :
我有以下查询：
db.somecollection.aggregate([{
$lookup: {
from: "campaigns",
localField: "campId",
foreignField: "_id",
as: "campaign"
}
}, {
$unwind: "$campaign"
}, {
$lookup: {
from: "entities",
localField: "campaign.clientid",
foreignField: "_id",
as: "campaign.client"
}
}]);
This request will return me this :
此请求将返回给我：
{
"_id" : ObjectId("56cc7cd1cc2cf62803ebfdc7"),
"campId" : ObjectId("56c740e4479f46e402efda84"),
"articleId" : ObjectId("56c742c06094640103ba3843"),
"campaign" : {
"_id" : ObjectId("56c740e4479f46e402efda84"),
"clientid" : ObjectId("56c740b8479f46e402efda83"),
"client" : [
{
"_id" : ObjectId("56c740b8479f46e402efda83"),
"username" : "someusername",
"shhh" : "somehashedpassword",
"email" : "[email protected]",
}
]
}
The request works well, but I would like to filter the fields in campaign.clientto only get for example _idand username. Is there a way to do this in a MongoDB aggregaterequest?
该请求运行良好，但我想过滤字段campaign.client以仅获取例如_id和username. 有没有办法在 MongoDBaggregate请求中做到这一点？
回答by Rodrigo Lopetegui
Just to help others with this, @SiddhartAjmera has the right answer, I only needed to add double quotes for nested values like "campaign.clientid".
只是为了帮助其他人，@SiddhartAjmera 有正确的答案，我只需要为“campaign.clientid”等嵌套值添加双引号。
The final code should be:
最终的代码应该是：
db.somecollection.aggregate([
{
"$lookup": {
"from": "campaigns",
"localField": "campId",
"foreignField": "_id",
"as": "campaign"
}
},
{
"$unwind": "$campaign"
},
{
"$lookup": {
"from": "entities",
"localField": "campaign.clientid",
"foreignField": "_id",
"as": "campaign.client"
}
},
{
"$project": {
"_id": 1,
"campId": 1,
"articleId": 1,
"campaign._id": 1,
"campaign.clientid": 1,
"campaign.client._id": 1,
"campaign.client.username": 1
}
}
]);
