MongoDb-如何精确搜索BSON复合密钥？

Question

I have a collection that stored information about devices like the following:

/* 1 */
{
  "_id" : {
    "startDate" : "2012-12-20",
    "endDate" : "2012-12-30",
    "dimensions" : ["manufacturer", "model"],
    "metrics" : ["deviceCount"]
  },
  "data" : {
    "results" : "1"
  }
}

/* 2 */
{
  "_id" : {
    "startDate" : "2012-12-20",
    "endDate" : "2012-12-30",
    "dimensions" : ["manufacturer", "model"],
    "metrics" : ["deviceCount", "noOfUsers"]
  },
  "data" : {
    "results" : "2"
  }
}

/* 3 */
{
  "_id" : {
    "dimensions" : ["manufacturer", "model"],
    "metrics" : ["deviceCount", "noOfUsers"]
  },
  "data" : {
    "results" : "3"
  }
}

And I am trying to query the documents using the _id field which will be unique. The problem I am having is that when I query for all the different attributes as in:

db.collection.find({$and: [{"_id.dimensions":{ $all: ["manufacturer","model"], $size: 2}}, {"_id.metrics": { $all:["noOfUsers","deviceCount"], $size: 2}}]});

This matches 2 and 3 documents (I don't care about the order of the attributes values), but I would like to only get 3 back. How can I say that there should not be any other attributes to _id than those that I specify in the search query?

Please advise. Thanks.

Answer 1

Unfortunately, I think the closest you can get to narrowing your query results to just unordered _id.dimensions and unordered _id.metrics requires you to know the other possible fields in the _id subdocument field, eg. startDate and endDate .

db.collection.find({$and: [
    {"_id.dimensions":{ $all: ["manufacturer","model"], $size: 2}}, 
    {"_id.metrics": { $all:["noOfUsers","deviceCount"], $size: 2}},
    {"_id.startDate":{$exists:false}},
    {"_id.endDate":{$exists:false}} 
]});

If you don't know the set of possible fields in _id , then the other possible solution would be to specify the exact _id that you want, eg.

db.collection.find({"_id" : {
    "dimensions" : ["manufacturer", "model"],
    "metrics" : ["deviceCount", "noOfUsers"]
}})

but this means that the order of _id.dimensions and _id.metrics is significant. This last query does a document match on exact BSON representation of _id .