Mongodb按复杂的计算值对文档进行排序 [英] Mongodb sort documents by complex computed value

问题描述

items = collection.aggregate([
        {"$match": {}},
        {"$project": {
            'temp_score': {
                "$add": ["$total_score", 100],
            },
            'temp_votes': {
                "$add": ["$total_votes", 20],
            },
            'weight': {
                "$divide": ["$temp_score", "$temp_votes"]
            }

            }
        }
    ])

total_score和total_votes已存储在文档中，

The total_score and total_votes have stored in the document,

我可以按预期获得temp_score和temp_votes，但是没有重量，有什么建议吗?

I can get temp_score and temp_votes as expected, but can't get weight, any suggestion?

推荐答案

您的$divide中还不存在您的$temp_score和$temp_votes.

Your $temp_score and $temp_votes are not existing yet in your $divide.

您可以再做一个$project:

db.user.aggregate([{
    "$project": {
        'temp_score': {
            "$add": ["$total_score", 100],
        },
        'temp_votes': {
            "$add": ["$total_votes", 20],
        }
    }
}, {
    "$project": {
        'temp_score':1,
        'temp_votes':1,
        'weight': {
            "$divide": ["$temp_score", "$temp_votes"]
        }
    }
}])

或重新计算$divide中的temp_score和temp_votes:

db.user.aggregate([{
    "$project": {
        'temp_score': {
            "$add": ["$total_score", 100],
        },
        'temp_votes': {
            "$add": ["$total_votes", 20],
        },
        'weight': {
            "$divide": [
                { "$add": ["$total_score", 100] },
                { "$add": ["$total_votes", 20] }
            ]
        }
    }
}]);

您还可以使用 $let运算符，该运算符将用于创建2个变量temp_score和temp_votes.但是结果将可以在一个字段(此处为total)下访问:

You can also do this in one single $project using the $let operator that will be used to create 2 variables temp_score and temp_votes. But the results will be accessible under a single field (here total) :

db.user.aggregate([{
    $project: {
        total: {
            $let: {
                vars: {
                    temp_score: { $add: ["$total_score", 100] },
                    temp_votes: { $add: ["$total_votes", 20] }
                },
                in : {
                    temp_score: "$$temp_score",
                    temp_votes: "$$temp_votes",
                    weight: { $divide: ["$$temp_score", "$$temp_votes"] }
                }
            }
        }
    }
}])

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