MONGODB Aggregate pipeline

having the following doc :

{ 
"_id" : ObjectId("xxx"), 
"seller" : {
    "phone" : {
        "number" : "xx"
    }, 
    "nickname" : "xx"
}, 
"shipping" : {
    "id" : xx
}, 
"id" : yyy, 
"order_items" : {
    "item" : {
        "title" : "xxxyy"
    }, 
    "quantity" : 1
}}

and i need to convert to this output

{ 
"_id" : ObjectId("xxx"), 
"seller.phone.number" : "xx",
"seller.nickname" : "xx", 
"shipping.id" : "xx",
"id" : yyy, 
"order_items.item.title" :"xxxyy",
"order_items.quantity" : 1
}

As you can see what i need to do is to flatten the document to a single level Im triying with the following code but mi output stills get nested

db.getCollection("collection").aggregate(
    [
        { 
            "$unwind" : { 
                "path" : "$order_items"
            }
        }, 
        { 
            "$project" : { 
                "seller.phone.number" : 1.0, 
                "seller.nickname" : 1.0, 
                "shipping.id" : 1.0, 
                "id" : 1.0, 
                "order_items.item.title" : 1.0, 
                "order_items.quantity" : 1.0
            }
        }
    ], 
    { 
        "allowDiskUse" : false
    }
);

Im starting to work with mongodb and studio3t any help would be appreciate regards

From the Mongo docs:

Otherwise, starting in MongoDB 3.6, the server permits storage of field names that contain dots (i.e. .) and dollar signs (i.e. $).

So while Mongo v3.6+ does allow for field names to contain dots they still provide the following warning:

Until support is added in the query language, the use of $ and . in field names is not recommended and is not supported by the official MongoDB drivers.

So studio3t has a custom driver they use as you can write queries in multiple languages but I believe they do just use the core drivers adjusted to your query language.

So what does this mean? this means the driver parses seller.phone.number as a nested object.

What you can do is change the field names in the project stage:

{
    "$project" : {
        "seller_phone_number": "$seller.phone.number",
        "seller_nickname": "$seller.nickname",
        "id": 1,
        "shipping_id": "$shipping.id",
        "order_item_quantity": "$order_items.quantity",
        "order_item_title": "$order_items.item.title",
    }
}