Mongodb returning multiple sub array results and e

问题:

I have the following collection with a node array:

{
"_id" : ObjectId("55acf6187d4c31475417fa62"),
"node" : [
    {
        "-id" : "29331496",
        "-uid" : "1899168",
        "-changeset" : "26313303",
        "-lat" : "-37.6104102",
        "-lon" : "144.9459817",
        "-timestamp" : "2014-10-25T03:36:51Z",
        "-user" : "heyitsstevo",
        "-visible" : "true",
        "-version" : "6"
    },
    {
        "-id" : "29331497",
        "-uid" : "1899168",
        "-version" : "2",
        "-lon" : "144.9451088",
        "-timestamp" : "2014-10-25T03:36:51Z",
        "-user" : "heyitsstevo",
        "-visible" : "true",
        "-changeset" : "26313303",
        "-lat" : "-37.601881"
    },
    {
        "-id" : "29331498",
        "-timestamp" : "2014-10-25T03:36:51Z",
        "-version" : "3",
        "-uid" : "1899168",
        "-user" : "heyitsstevo",
        "-visible" : "true",
        "-changeset" : "26313303",
        "-lat" : "-37.6011267",
        "-lon" : "144.9448575"
    },
    {
        "-lon" : "144.943302",
        "-id" : "29331499",
        "-timestamp" : "2011-11-23T03:21:40Z",
        "-user" : "melb_guy",
        "-version" : "9",
        "-uid" : "11111",
        "-visible" : "true",
        "-changeset" : "9916439",
        "-lat" : "-37.5983291"
    },
    {
        "-id" : "60648717",
        "-uid" : "46482",
        "-user" : "Zulu99",
        "-lat" : "-37.6796337",
        "-lon" : "144.9220639",
        "-timestamp" : "2009-12-12T21:29:36Z",
        "-visible" : "true",
        "-version" : "2",
        "-changeset" : "3358816"
    },
    {
        "-id" : "60648718",
        "-timestamp" : "2009-12-12T21:29:35Z",
        "-uid" : "46482",
        "-version" : "2",
        "-changeset" : "3358816",
        "-user" : "Zulu99",
        "-visible" : "true",
        "-lat" : "-37.6787103",
        "-lon" : "144.9224609"
    },
    {
        "-id" : "60648719",
        "-timestamp" : "2009-12-12T21:28:58Z",
        "-user" : "Leon K",
        "-version" : "2",
        "-changeset" : "3358816",
        "-uid" : "Zulu99",
        "-visible" : "true",
        "-lat" : "-37.677841",
        "-lon" : "144.9227344"
    }
]
}

How do I return all nodes that have the "-user" = "Zulu99" and exclude anything else?

I have tried the following query but it only returns the first node it finds with "Zulu99":

db.osm.find( { }, { node: {$elemMatch: {'-user': 'Zulu99'}}} )

回答1:

If your documents size more then aggregation $unwind creates Cartesian Product problem i.e every array object creates multiple documents so it creates slow down aggregation query, If you want avoid this problem use $redact as like below :

db.collectionName.aggregate({
  "$match": {
    "node.-user": "Zulu99"
  }
}, {
  "$redact": {
    "$cond": {
      "if": {
        "$eq": [{
          "$ifNull": ["$-user", "Zulu99"]
        }, "Zulu99"]
      },
      "then": "$$DESCEND",
      "else": "$$PRUNE"
    }
  }
}).pretty()

---

EDIT

If you want to multiple conditions then used $cond with $and like this

db.collectionName.aggregate({
  "$match": {
    "node.-user": "Zulu99",
    "node.-lat": "-37.6787103"
  }
}, {
  "$redact": {
    "$cond": {
      "if": {
        "$and": [{
          "$eq": [{
            "$ifNull": ["$-user", "Zulu99"]
          }, "Zulu99"]
        }, {
          "$eq": [{
            "$ifNull": ["$-lat", "-37.6787103"]
          }, "-37.6787103"]
        }]
      },
      "then": "$$DESCEND",
      "else": "$$PRUNE"
    }
  }
}).pretty()

In above query you get that lat check whether is equal to -37.6787103 or not, if you want to check -lat and -lon to $gt or $lt then first you should changed your data type of both lat and lon in your documents it looks like String so first changed data type String to number then used comparison operator.

Second things if you want only matched node array object then used group after readact like this :

db.collectionName.aggregate({
  "$match": {
    "node.-user": "Zulu99",
    "node.-lat": "-37.6787103"
  }
}, {
  "$redact": {
    "$cond": {
      "if": {
        "$and": [{
          "$eq": [{
            "$ifNull": ["$-user", "Zulu99"]
          }, "Zulu99"]
        }, {
          "$eq": [{
            "$ifNull": ["$-lat", "-37.6787103"]
          }, "-37.6787103"]
        }]
      },
      "then": "$$DESCEND",
      "else": "$$PRUNE"
    }
  }
}, {
  "$group": {
    "_id": "$_id",
    "node": {
      "$first": "$node" // use $first 
    }
  }
}).pretty()

New Edit

If you want to find out gte and lte condition then follow this aggregation :

db.collectionName.aggregate({
"$project": {
 "check": {
  "$setDifference": [{
      "$map": {
        "input": "$node",
        "as": "node1",
        "in": {
          "$cond": {
            "if": {
              "$and": [{
                "$and": [{
                  "$gte": ["$$node1.-lon", 100]
                }, {
                  "$lte": ["$$node1.-lon", 150]
                }]
              }, {
                "$and": [{
                  "$gte": ["$$node1.-lat", -50]
                }, {
                  "$lte": ["$$node1.-lat", -10]
                }]
              }]
            },
            "then": "$$node1",
            "else": false
          }
        }
      }
    },
    [false]
  ]
 }
}
}).pretty()

回答2:

What you need is "aggregation" and the $map and the $setDifference operators

db.collection.aggregate([ 
    { 
        "$match": { 
            "node.-user": "Zulu99", 
            "node.-lat": "-37.6787103" 
        }
    },
    { 
        "$project": { 
            "node": { 
                "$setDifference": [{ 
                    "$map": { 
                        "input": "$node",
                        "as": "n", 
                        "in": { 
                            "$cond": [
                                { "$eq": [ "$$n.-user", "Zulu99" ]}, 
                                "$$n", 
                                false 
                            ]
                        } 
                    }
                }, 
                [false]]
            }
        }
    }
])

---

From MongoDB 3.2 you can use the $filter operator

db.collection.aggregate([
    { 
        "$match":  { 
            "node.-user": "Zulu99",
            "node.-lat": "-37.6787103"
        }
    }, 
    { "$project": {
        "node": {
            "$filter": {
                "input": "$node",
                "as": "n",
                "cond": { "$eq": [ "$$node.n", "Zulu99" ] }
            }
        }
    }}
])

which yields:

{
        "_id" : ObjectId("55acf6187d4c31475417fa62"),
        "node" : [
                {
                        "-id" : "60648717",
                        "-uid" : "46482",
                        "-user" : "Zulu99",
                        "-lat" : "-37.6796337",
                        "-lon" : "144.9220639",
                        "-timestamp" : "2009-12-12T21:29:36Z",
                        "-visible" : "true",
                        "-version" : "2",
                        "-changeset" : "3358816"
                },
                {
                        "-id" : "60648718",
                        "-timestamp" : "2009-12-12T21:29:35Z",
                        "-uid" : "46482",
                        "-version" : "2",
                        "-changeset" : "3358816",
                        "-user" : "Zulu99",
                        "-visible" : "true",
                        "-lat" : "-37.6787103",
                        "-lon" : "144.9224609"
                }
        ]
}