MongoDB Querying Nested Arrays

Question

I'm having some trouble with querying a Mongo Collection.

I have a Collection like this:

{
"_id" : "555bd34329de3cf232434ef2",
"cars" : [ 
    {
        "0" : {
            "parts" : [ 
                {
                    "name" : "x1",
                    "price" : 12
                },
                {
                    "name" : "x2",
                    "price" : 14
                }
            ]
        },
        "1" : {
            "parts" : [ 
                {
                    "name" : "y1",
                    "price" : 8
                },
                {
                    "name" : "y2",
                    "price" : 12
                }
            ]
        } 
    }
]
}

I'd like to return just the following:

"parts" : [ 
    {
        "name" : "x1",
        "price" : 12
    },
    {
        "name" : "x2",
        "price" : 14
    }
]

In other words, I need to figure out how to query the Collection by two parameters at the same time:

where the ID matches "555bd34329de3cf232434ef2"
where the "name" of the part matches "x1"

Does anyone know how to do this kind of nested query?

Don't hesitate to create multiple collections, you could have a collection Parts, Cars and GroupsOfCars. It is a good practice adviced by Meteor: https://guide.meteor.com/collections.html#schema-design And it makes the query easier — Gaëtan Rouziès, Feb 07 '18 at 12:26
That "0" and "1" inside your "cars" array... Should that be array indices or are those really fields in a single nested document that you keep inside your "cars" array? — dnickless, Feb 07 '18 at 12:43
It looks like you don't need the `cars` array, doesn't it? The `parts` array could be at the document root, or at least that's what appears from your code. That would simplify things. — Miguel Calderón, Feb 07 '18 at 12:47
There are other fields at the document root that I have excluded for the sake of example. In any case, I agree it's best that I move "cars" to a separate Collection. — Nick Andrews, Feb 07 '18 at 12:51

score 0 · Accepted Answer · answered Feb 07 '18 at 12:52

Assuming a document structure like this:

{
    "_id" : ObjectId("555bd34329de3cf232434ef2"),
    "cars" : [ 
        {
            "parts" : [ 
                {
                    "name" : "x1",
                    "price" : 12
                }, 
                {
                    "name" : "x2",
                    "price" : 14
                }
            ]
        }, 
        {
            "parts" : [ 
                {
                    "name" : "y1",
                    "price" : 8
                }, 
                {
                    "name" : "y2",
                    "price" : 12
                }
            ]
        }
    ]
}

you can run the following query:

db.collection.find({ "_id": ObjectId("555bd34329de3cf232434ef2"), "cars.parts.name" : "x1" }, { "_id": 0, "cars.$": 1 })

which will get you pretty close to where you want to be:

{
    "cars" : [ 
        {
            "parts" : [ 
                {
                    "name" : "x1",
                    "price" : 12
                }, 
                {
                    "name" : "x2",
                    "price" : 14
                }
            ]
        }
    ]
}

You could get closer using the aggregation framework if that's not good enough...

MongoDB Querying Nested Arrays

1 Answers1