Mongodb Meteor Querying Array and getting object

Question

I have one collection called Resources with documents inside:

{
    "_id" : "fGR4ECcw5p2HFgxd3",
    "ownerId" : "J8MpsWChPQdET6jwQ",
    "inventory" : [ 
        {
            "_id" : ObjectId("5b537ef5895adfeae037e0a4"),
            "quantity" : 17
        }, 
        {
            "_id" : ObjectId("5b537d9c895adfeae037dbd2"),
            "quantity" : 6
        }, 
        {
            "_id" : ObjectId("5b5868e081702f675304290e"),
            "quantity" : 26
        }, 
        {
            "_id" : ObjectId("5b5eba8276dd90bd75e27f13"),
            "quantity" : 85
        }, 
        {
            "_id" : ObjectId("5b5ee58176dd90bd75e2f35f"),
            "quantity" : 5
        }, 
        {
            "_id" : ObjectId("5b62275686f92e050a9d50b2"),
            "quantity" : 3
        }
    ]
}

What i am trying to do is get object of inventory array with that objects id

I feel like this should work but its not

Resources.findOne({ownerId:userid,"inventory._id":ObjectId})

my expected output for example:

 {
            "_id" : ObjectId("5b537ef5895adfeae037e0a4"),
            "quantity" : 17
        }

I also tried this:

 console.log(Resources.findOne({ownerId:userid},{fields:{inventory:{$elemMatch:{_id:ids[i]}}}}));

Ashh · Accepted Answer · 2018-08-04 08:28:30Z

2

You can try this

db.collection.find({
  "ownerId": "J8MpsWChPQdET6jwQ"
},
{
  "inventory": {
    "$elemMatch": {
      "_id": ObjectId("5b537ef5895adfeae037e0a4")
    }
  }
})

Try it here

answered Aug 4, 2018 at 8:28

Ashh

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Comments

Carlo Espino · Accepted Answer · 2018-08-03 23:23:53Z

You can use MongoDB aggregations as per documetation:

Aggregation operations process data records and return computed results. Aggregation operations group values from multiple documents together, and can perform a variety of operations on the grouped data to return a single result.

Please make sure meteor has proper interface to MongoDB aggregations i.e. Resources.aggregate

Later mongo shell query works on my machine with the document you mentioned.

db.test.aggregate([
    {
        $match: {
            ownerId: "J8MpsWChPQdET6jwQ",
            inventory: {
                $elemMatch: {
                    "_id": ObjectId("5b537ef5895adfeae037e0a4")
                }
            }
        }
    },
    {
        $project: {
            _id: 0,
            inventory: 1
        }
    },
    {
        $project: {
            result:
            {
                $arrayElemAt: [
                    {
                        $filter: {
                            input: "$inventory",
                            as: "product",
                            cond: {
                                $eq: [
                                    "$$product._id",
                                    ObjectId("5b537ef5895adfeae037e0a4")
                                ]
                            }
                        }
                    },
                    0
                ]
            }
        }
    }
])

Result is:

{
        "result" : {
                "_id" : ObjectId("5b537ef5895adfeae037e0a4"),
                "quantity" : 17
        }
}

Kieran McWilliams · Accepted Answer · 2018-08-03 23:24:06Z

1

Assuming you just want to access that data, there is an easier way.

You can grab the resource, then run through it's inventory and find the object you want.

Try something like this (userId and objectId are your input/searching variables. I also camel-cased them):

var userId = "some id";
var objectId = "some id";

var resource = Resources.findOne({"ownerId": userId});
var inventory = resource.inventory;

var output = {};

for(var i = 0; i < inventory.length; i++) {
  if(inventory[i]._id == objectId) {
    output = inventory[i];
  }
}

answered Aug 3, 2018 at 23:24

Kieran McWilliams

1018 bronze badges

2 Comments

l0veisreal Over a year ago

first i was doing like that but what about speed isnt it faster with mongo query ?

Kieran McWilliams Over a year ago

Ah, that could be true, but I do not know for sure. Honestly unless you're dealing with some mammoth data it shouldn't be an issue, and this is cleaner code-wise imo. Maybe try both out and see

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