带有$lookup的MongoDB聚合只包括(或项目)从查询返回的一些字段
在mongo中,在使用带有$lookup的MongoDB聚合只包括(或项目)从查询返回的一些字段,mongodb,aggregation-framework,lookup,Mongodb,Aggregation Framework,Lookup,在mongo中,在使用$lookup进行聚合之后,我希望请求只返回一些字段,而不是整个文档 我有以下疑问: db.somecollection.aggregate([{ $lookup: { from: "campaigns", localField: "campId", foreignField: "_id", as: "campaign" } }, { $unwind: "$campaign" }, {
$lookup
进行聚合之后,我希望请求只返回一些字段,而不是整个文档
我有以下疑问:
db.somecollection.aggregate([{
$lookup: {
from: "campaigns",
localField: "campId",
foreignField: "_id",
as: "campaign"
}
}, {
$unwind: "$campaign"
}, {
$lookup: {
from: "entities",
localField: "campaign.clientid",
foreignField: "_id",
as: "campaign.client"
}
}]);
此请求将返回以下内容:
{
"_id" : ObjectId("56cc7cd1cc2cf62803ebfdc7"),
"campId" : ObjectId("56c740e4479f46e402efda84"),
"articleId" : ObjectId("56c742c06094640103ba3843"),
"campaign" : {
"_id" : ObjectId("56c740e4479f46e402efda84"),
"clientid" : ObjectId("56c740b8479f46e402efda83"),
"client" : [
{
"_id" : ObjectId("56c740b8479f46e402efda83"),
"username" : "someusername",
"shhh" : "somehashedpassword",
"email" : "mail@mail.com",
}
]
}
请求运行良好,但我想筛选活动.client
中的字段,以便仅获取例如\u id
和用户名
。在MongoDB聚合请求中是否有这样做的方法?为了帮助其他人,@SiddhartAjmera给出了正确的答案,我只需要为嵌套值添加双引号,如“campaign.clientid”
最终代码应为:
db.somecollection.aggregate([
{
"$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
}
}
]);
只需在前面的答案中添加一点:您可以将0添加到要忽略的项目项中,其余的将被检索,因此您不需要使用1来编写所有列表:
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"
}
},
{
"$project": {
"campaign.client.shhh": 0
}
}
])
在$lookup
db.somecollection.aggregate([{
$lookup: {
from: "campaigns",
localField: "campId",
foreignField: "_id",
as: "campaign"
}
}, {
$unwind: "$campaign"
}, {
$lookup: {
from: "entities",
let: { client_id: "$campaign.clientid" },
pipeline : [
{ $match: { $expr: { $eq: [ "$_id", "$$client_id" ] } }, },
{ $project : { _id:1, username:1 } }
],
as: "campaign.client"
}
}]);
我知道现在回答这个问题已经很晚了。但在我看来,更新有时是非常有益的。
项目阶段很好,但您仍然会在$lookup
阶段请求整个dock。字段仅在其后面的投影阶段中过滤。
MongoDB 3.6发布后,现在可以向$lookup
阶段添加管道,以指定多个连接条件。在他们的官方文档中查找更多详细信息。
您可以按如下方式转换聚合管道,以获得所需的结果:
db.somecollection.aggregate([{
$lookup: {
from: "campaigns",
localField: "campId",
foreignField: "_id",
as: "campaign"
}
}, {
$unwind: "$campaign"
}, {
$lookup: {
from: "entities",
let: {clientid: '$campaign.clientid'},
pipeline: [
{ '$match':
{ '$expr':
{
'$eq': ['$_id', '$$clientid']
}
}
},
{ '$project':
'_id': 1,
'username': 1
}
]
as: "campaign.client"
}
}]);
这样,您就可以在$lookup
阶段内过滤加入集合的字段。
请注意内部管道的$match
阶段内的$
符号。它用于表示在let
块中定义的自定义字段。
使用$project
阶段<代码>{$project:{{u id:1,campId:1,articleId:1,活动。{u id:1,campaign.clientid:1,campaign.client.{u id:1,campaign.client.username:1}}
@SiddharthAjmera你应该把它转换成一个答案,你刚刚救了我的一天!为什么我们要添加$unwind?为什么需要它?@Faisal它会以数组的形式返回活动,如果你不做$unwind…有没有办法只从父项返回所有内容(在项目中),从子项返回特定字段。(我用“*”作为指示符)例如:$project:{“*”:1,“campaign.\u id”:1,“campaign.clientid”:1,“campaign.client.\u id”:1,“campaign.client.username”:1}@mliscetrus你找到方法了吗?@mliscetrus AlpeshVasani你找到方法了吗?