CODEWITHSUNDEEP
mongodbmongodb-queryaggregation-frameworkaggregation
user1408681
user1408681

Reputation:

MongoDB - use document field as variable

I have documents with structure similar to this:

{
    users_ids: [
        "122djdj-sdsddsl-3232323",
        "2332333-443rdds-sdadads"
    ],
    users_roles: {
        "122djdj-sdsddsl-3232323": "admin",
        "2332333-443rdds-sdadads": "moderator"
    },
    users_names: {
        "122djdj-sdsddsl-3232323": "John Smith",
        "2332333-443rdds-sdadads": "Paul Newman"
    }
}

users_ids is array with users, then are objects with different properties. Now, I would like to make query and get document with additional fields like:

adminId: 122djdj-sdsddsl-3232323
adminName: John Smith

All these fields will be non-dynamic, i.e. will be defined in query. I need them to sort values using for example admin name (so I first must know, who is admin, then add field with admin name). My question: how can I use field from document in other expressions? I though about first add fields:

{
    $addFields: {
        userA: { $arrayElemAt: ["$users_ids", 0] },
        userB: { $arrayElemAt: ["$users_ids", 1] },
    }
}

And then use $userA and $userB in other conditions - but any method doesn't work, also tried $objectToArray without success:

{
    $addFields: {
        roles: { $objectToArray: "$users_roles" }
    }
},
{
    $addFields: {
        // Doesnt work
        adminName: {
            $cond: {
                if: {
                    $eq: ["$roles[0].v", 'admin']
                },
                then: "$roles[0].k",
                else: "$roles[1].k"
            }
        }
    }
}

Upvotes: 1

Views: 220

Answers (1)

mickl
mickl

Reputation: 49945

You have to start with $objectToArray since your key names are dynamic (you can rethink that design). Then you need to run a combination of $arrayElemAt and $filter to get first matching element:

db.collection.aggregate([
    {
        $addFields: {
            user_roles_arr: { $objectToArray: "$users_roles" },
            user_names_arr: { $objectToArray: "$users_names" },
        }
    },
    {
        $addFields: {
            admin: {
                $arrayElemAt: [
                    { $filter: { input: "$user_roles_arr", cond: { $eq: [ "$$this.v", "admin" ] } } }, 0
                ]
            }
        }
    },
    {
        $addFields: {
            adminId: "$admin.k",
            adminName: {
                $let: {
                    vars: { adm: { $arrayElemAt: [ { $filter: { input: "$user_names_arr", cond: { $eq: [ "$admin.k", "$$this.k" ] } } }, 0 ]  } },
                    in: "$$adm.v"
                }
            }
        }
    },
    {
        $project: {
            user_roles_arr: 0,
            user_names_arr: 0,
            admin: 0
        }
    }
])

Mongo Playground

Upvotes: 0

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