Retrieve only ObjectIds that are embedded in an Array using MongoDB's .find() method

Question

Retrieve only ObjectIds that are embedded in an Array using MongoDB's .find() method

I am looking to extract only the ObjectIds from a specific document that is nested within the projects Array. I am working on creating a database where each user will have their own set of projects. Thank you!

db.users.find().pretty()
{
    "_id" : ObjectId("5762c0cf2b9a78006373a684"),
    "name" : "seq",
    "pass" : "seq",
    "projects" : [
        {
            "pid" : ObjectId("5762c0ba2b9a78006373a682"),
            "name" : "aaa"
        },
        {
            "pid" : ObjectId("5762c0ba2b9a78006373a683"),
            "name" : "bbb"
        }
    ]
}
{
    "_id" : ObjectId("5762c28d2b9a78006373a687"),
    "name" : "leq",
    "pass" : "leq",
    "projects" : [
        {
            "pid" : ObjectId("5762c2892b9a78006373a685"),
            "name" : "ccc"
        },
        {
            "pid" : ObjectId("5762c2892b9a78006373a686"),
            "name" : "ddd"
        }
    ]
}

javascript arrays mongodb

Answer 1

Answer №1

Let's consider the scenario where we need to retrieve two PIDs.

{"pid" : ObjectId("5762c0ba2b9a78006373a682")} and {"pid" : ObjectId("5762c2892b9a78006373a686"),}

Specifically, we are interested in extracting inner documents only.

Therefore, the expected response should be as follows:

{
    "_id" : ObjectId("5762c0ba2b9a78006373a682"),
    "name" : "aaa"
},{
    "_id" : ObjectId("5762c2892b9a78006373a686"),
    "name" : "ddd"
}

The Aggregation framework has the ability to manipulate documents, filter only the necessary ones, and alter the internal structure during the project phase:

var match = {
    $match : {
        "projects.pid" : {
            $in : [ObjectId("5762c0ba2b9a78006373a682"), 
                   ObjectId("5762c2892b9a78006373a686")]
        }
    }
}
var unwind = {
    $unwind : "$projects"
};

// move the array object to the top level
var project = {
    $project : {
        _id : "$projects.pid",
        name : "$projects.name",
        // include other fields as needed
    }
}
db.vic.aggregate([match, unwind, match, project])

Answer 2

Let's consider the scenario where we need to retrieve two PIDs.

{"pid" : ObjectId("5762c0ba2b9a78006373a682")} and {"pid" : ObjectId("5762c2892b9a78006373a686"),}

Specifically, we are interested in extracting inner documents only.

Therefore, the expected response should be as follows:

{
    "_id" : ObjectId("5762c0ba2b9a78006373a682"),
    "name" : "aaa"
},{
    "_id" : ObjectId("5762c2892b9a78006373a686"),
    "name" : "ddd"
}

The Aggregation framework has the ability to manipulate documents, filter only the necessary ones, and alter the internal structure during the project phase:

var match = {
    $match : {
        "projects.pid" : {
            $in : [ObjectId("5762c0ba2b9a78006373a682"), 
                   ObjectId("5762c2892b9a78006373a686")]
        }
    }
}
var unwind = {
    $unwind : "$projects"
};

// move the array object to the top level
var project = {
    $project : {
        _id : "$projects.pid",
        name : "$projects.name",
        // include other fields as needed
    }
}
db.vic.aggregate([match, unwind, match, project])

Retrieve only ObjectIds that are embedded in an Array using MongoDB's .find() method

Answer №1

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