在mongodb的另一个查询中使用上一个查询的结果 [英] Use result from previous query in another query in mongodb

问题描述

第一个查询:

    db.a.find({
    "type": ObjectId("50ed90f5a70defef23000002"),
    "config.name": "alpha"
 }, {
    "user": 1
 })

第一个查询结果:

{ "_id" : ObjectId("5684035c91b4693b39547591"), "user" : ObjectId("54ba80ac2735eea200623612") }

第二个查询:

   db.users.find({
    "_id": ObjectId("54ba80ac2735eea200623612")
}, {
    "lastname": 1
})

我可以将这两个查询合并为一个查询吗?第二查询使用第一查询结果的"user"值ObjectId("54ba80ac2735eea200623612")

can I combine these two queries into one query? 2st query uses 1st query result's "user" value ObjectId("54ba80ac2735eea200623612")

推荐答案

您可以使用带有$match的聚合来匹配您的条件，并且可以使用$lookup将本地字段user映射到您的user集合_id字段:

You can use an aggregation with a $match to match your condition and $lookup to map your local field user to your usercollection _id field :

db.a.aggregate(
    [{
        $match: {
            "type": ObjectId("50ed90f5a70defef23000002"),
            "config.name": "alpha"
        }
    }, {
        $lookup: {
            from: "users",
            localField: "user",
            foreignField: "_id",
            as: "users"
        }
    }, {
        $unwind: "$users"
    }]);

例如，在Javascript中，可以使用mongoose来完成此操作:

In Javascript, with mongoose for example you can do this with :

YourModel.aggregate(
    [{
        $match: {
            "type": ObjectId("50ed90f5a70defef23000002"),
            "config.name": "alpha"
        }
    }, {
        $lookup: {
            from: "users",
            localField: "user",
            foreignField: "_id",
            as: "users"
        }
    }, {
        $unwind: "$users"
    }],
    function(err, result) {
        console.log("lastname : " + result.users.lastname);
    });

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