MongoDB將對象ID從一個集合添加到另一個

Question

我有mongodb collection1 ，如下所示

{
        "_id" : ObjectId("5a7286c9bcf16750f621007b"),
        "host" : "host1",
        "column2" : "value2",
        "column3" : 6,
        "date_created" : "2015-01-25 00:00:00"
}

我有mongodb collection2 ，如下所示

{
        "_id" : ObjectId("5a728429bcf16750f62056e8"),
        "hostname" : "host1",
        "column2" : 322,
        "column3" : 81,
}

{
        "_id" : ObjectId("5a728429cde16750f62056e8"),
        "hostname" : "host1",
        "column2" : 312,
        "column3" : 89,
}

我想補充field在collection2命名為collection1_id ，使得hostname在collection2匹配host在collection1

我的輸出應該如下

{
        "_id" : ObjectId("5a728429bcf16750f62056e8"),
        "hostname" : "host1",
        "column2" : 322,
        "column3" : 81,
        "collection1_id" : ObjectId("5a7286c9bcf16750f621007b")  

}

{
        "_id" : ObjectId("5a728429cde16750f62056e8"),
        "hostname" : "host1",
        "column2" : 312,
        "column3" : 89,
        "collection1_id" : ObjectId("5a7286c9bcf16750f621007b") 
}

我現在所知道的是我將需要運行db.collection2.update()

Answer 1

您可以使用聚合管道$lookup並使用結果光標更新collection2中的_id

管道

db.co2.aggregate(
    [
        {$lookup : {from : "co1", localField : "hostname", foreignField : "host", as : "collection1_id"}},
        {$addFields : {collection1_id : {$arrayElemAt : ["$collection1_id._id" , 0]}}}
    ]
).pretty()

結果

> db.co2.aggregate([{$lookup : {from : "co1", localField : "hostname", foreignField : "host", as : "collection1_id"}},{$addFields : {collection1_id : {$arrayElemAt : ["$collection1_id._id" , 0]}}}]).pretty()
{
    "_id" : ObjectId("5a728429bcf16750f62056e8"),
    "hostname" : "host1",
    "column2" : 322,
    "column3" : 81,
    "collection1_id" : ObjectId("5a7286c9bcf16750f621007b")
}
{
    "_id" : ObjectId("5a728429cde16750f62056e8"),
    "hostname" : "host1",
    "column2" : 312,
    "column3" : 89,
    "collection1_id" : ObjectId("5a7286c9bcf16750f621007b")
}
> 

編輯

適用於mongo 3.4及更低版本

用$project代替$addFields

db.co2.aggregate(
    [
        {$lookup : {from : "co1", localField : "hostname", foreignField : "host", as : "collection1_id"}},
        {$project : {hostname : 1, column2 : 1, column3 : 1, collection1_id : {$arrayElemAt : ["$collection1_id._id" , 0]}}}
    ]
).pretty()