在mongo中,对$lookup执行aggregation后,我希望请求仅返回某些字段,而不返回整个文档.
我有以下查询:
db.somecollection.aggregate([{ $lookup: { from: "campaigns", localField: "campId", foreignField: "_id", as: "campaign" } }, { $unwind: "$campaign" }, { $lookup: { from: "entities", localField: "campaign.clientid", foreignField: "_id", as: "campaign.client" } }]);此请求将向我返回此:
{ "_id" : ObjectId("56cc7cd1cc2cf62803ebfdc7"), "campId" : ObjectId("56c740e4479f46e402efda84"), "articleId" : ObjectId("56c742c06094640103ba3843"), "campaign" : { "_id" : ObjectId("56c740e4479f46e402efda84"), "clientid" : ObjectId("56c740b8479f46e402efda83"), "client" : [ { "_id" : ObjectId("56c740b8479f46e402efda83"), "username" : "someusername", "shhh" : "somehashedpassword", "email" : "mail@mail", } ] }该请求运行良好,但我想过滤campaign.client中的字段,以仅获取例如_id和username的字段.有没有办法在MongoDB aggregate请求中做到这一点?
解决方案@SiddhartAjmera只是为了帮助他人,我的答案是正确的,我只需要为"campaign.clientid"之类的嵌套值添加双引号即可. >
最终代码应为:
db.somecollection.aggregate([ { "$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 } } ]);In mongo, after doing an aggregation with $lookup, I would like the request to return only some fields and not the whole document.
I have the following query :
db.somecollection.aggregate([{ $lookup: { from: "campaigns", localField: "campId", foreignField: "_id", as: "campaign" } }, { $unwind: "$campaign" }, { $lookup: { from: "entities", localField: "campaign.clientid", foreignField: "_id", as: "campaign.client" } }]);This request will return me this :
{ "_id" : ObjectId("56cc7cd1cc2cf62803ebfdc7"), "campId" : ObjectId("56c740e4479f46e402efda84"), "articleId" : ObjectId("56c742c06094640103ba3843"), "campaign" : { "_id" : ObjectId("56c740e4479f46e402efda84"), "clientid" : ObjectId("56c740b8479f46e402efda83"), "client" : [ { "_id" : ObjectId("56c740b8479f46e402efda83"), "username" : "someusername", "shhh" : "somehashedpassword", "email" : "mail@mail", } ] }The request works well, but I would like to filter the fields in campaign.client to only get for example _id and username. Is there a way to do this in a MongoDB aggregate request?
解决方案Just to help others with this, @SiddhartAjmera has the right answer, I only needed to add double quotes for nested values like "campaign.clientid".
The final code should be:
db.somecollection.aggregate([ { "$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 } } ]);
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