使用查询MongoDb创建数组

Question

我有这个收藏

{
    "_id" : ObjectId("55555555ffffff000010200a"),  
    "name" : "foo"
}

{
    "_id" : ObjectId("55555555ffffff000010200e"),
    "name" : "bar"
}

{
    "_id" : ObjectId("55555555ffffff000010200f"),    
    "name" : "baz"
}


{
    "_id" : ObjectId("55555555ffffff000010200b"),
    "name" : "biz"
}

我想要一个数组ID

我这样做了

db.mycollection.find({}, {_id: 1})

并返回

{
    "_id" : ObjectId("55555555ffffff000010200a")
}

{
    "_id" : ObjectId("55555555ffffff000010200e")
}

{
    "_id" : ObjectId("55555555ffffff000010200f")
}

{
    "_id" : ObjectId("55555555ffffff000010200b")
}

{
    "_id" : ObjectId("55555555ffffff000010200c")
}

{
    "_id" : ObjectId("55555555ffffff0000103111")
}

我可以有阵列吗？ID [ '55555555ffffff0000103111', '55555555ffffff0000103111', '555555555ffffff0000103111', '55555555ffffff0000103111']

Answer 1

选项1:如果可以接受子文档数组,则只需将.toArray()附加到查询查询即可.

> db.test.find({}, {_id:1}).toArray()
[
        {
                "_id" : ObjectId("53270b12d111b9bf595f4270")
        },
        {
                "_id" : ObjectId("53270b14d111b9bf595f4271")
        },
        {
                "_id" : ObjectId("53270b16d111b9bf595f4272")
        }
]

选项2:另一种选择是使用聚合框架.

> db.test.aggregate([{$group:{_id:null, ids:{$push:"$_id"}}}, {$project:{_id:0, ids:1}}])
{
        "result" : [
                {
                        "ids" : [
                                ObjectId("53270b12d111b9bf595f4270"),
                                ObjectId("53270b14d111b9bf595f4271"),
                                ObjectId("53270b16d111b9bf595f4272")
                        ]
                }
        ],
        "ok" : 1
}

选项3:或者您可以在shell中使用forEach,如下所示:

> var myIds = new Array()
> db.test.find({},{_id:1}).forEach(function(myDoc){myIds.push(myDoc._id.str)})
> myIds
[
        "53270b12d111b9bf595f4270",
        "53270b14d111b9bf595f4271",
        "53270b16d111b9bf595f4272"
]