在 MongoDB 的实例数组中仅拉取一项？

Question

I'm working with MongoDB (by using Mongoose on NodeJS).

{
"_id":{"$oid":"5fa4386f3a93dc470c920d76"},
"characters":[
    {"$oid":"5fa4389e3a93dc470c920d78"},
    {"$oid":"5fa4389e3a88888888888888"},
    {"$oid":"5fa4389e3a88888888888888"},
    {"$oid":"5fa4389e3a88888888888888"}
    ]
}

I tried to remove only one row of object id "5fa4389e3a88888888888888" in my characters array. By doing..

User.findByIdAndUpdate("5fa4386f3a93dc470c920d76", { $pull: { characters: "5fa4389e3a88888888888888" } }, (err) => {});

The problem is that every row with "5fa4389e3a88888888888888" value are removed. And I'd just like to pull 1.

Is it possible?

Thanks for helping

Answer 1

You can use update with aggregation pipeline , and use the $function operator to define custom functions to implement behavior not supported by the MongoDB Query Language. Starting from MongoDB v4.4,

User.findByIdAndUpdate("5fa4386f3a93dc470c920d76",
[
    {
        $set: {
            characters: {
                $function: {
                    body: function(characters) {
                        for (var i=0; i<characters.length; i++) {
                            if (characters[i] == "5fa4389e3a88888888888888") {
                                delete characters[i];
                                break;
                            }
                        }
                        return characters;
                    },
                    args: ["$characters"],
                    lang: "js"
                }
            }
        }
    }
])