如何计算列表清单中的项目 [英] How to count items in list of lists

问题描述

我如何在"mol"列表中找到每个项目的长度:

How i can find length of each item in a "mol"list:

例如，如果我正在寻找"versionA" : "2.1.2"，我希望获得以下结果:

For example if I am looking for "versionA" : "2.1.2" I expect ot get following result:

{"project" : "A", "scene" : 13455312, mol:[3,2,1]},
{"project" : "B", "scene" : 13455344, mol:[3,3,3]}

我的数据:

{
        "project" : "A",
        "scene" : 13455312,
        "versionA" : "2.1.2",
        "versionB" : "2.1.9",
        "mol" : [ {"data" : [ { "tran" : 'A' }, { "tran" : 'B' }, { "tran" : 'C' }]}, {"data" : [ { "tran" : 'A' }, { "tran" : 'B' }]}, {"data" : [ { "tran" : 'A' }]}]
    },

    {
        "project" : "B",
        "scene" : 13455344,
        "versionA" : "2.1.2",
        "versionB" : "2.1.9",
        "mol" : [ {"data" : [ { "tran" : 'A' }, { "tran" : 'B' }, { "tran" : 'C' }]}, {"data" : [ { "tran" : 'A' }, { "tran" : 'B' }, { "tran" : 'C' }]}, {"data" : [ { "tran" : 'A' }, { "tran" : 'B' }, { "tran" : 'C' }]}]
    },
    {
        "project" : "C",
        "scene" : 135555,
        "versionA" : "2.1.3",
        "versionB" : "2.1.9",
        "mol" : [ {"data" : [ { "tran" : 'A' }]}, {"data" : [ { "tran" : 'A' }]}, {"data" : [ { "tran" : 'A' }]}]
    }

推荐答案

您可以$match到version字段，然后$map迭代mol和$size以计算数据字段的长度

You can $match to the version field and $map which iterates the mol and $size to calculate the the length of data field.

db.collection.aggregate(
    [{
        $match: {
            "versionA": "2.1.2"
        }
    }, {
        $project: {
            _id: 0,
            "project": 1,
            "scene": 1,
            "mol": {
                $map: {
                    input: "$mol",
                    as: "mo",
                    in: {
                        $size: "$$mo.data"
                    }
                }
            }
        }
    }]
)

这篇关于如何计算列表清单中的项目的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！