Mongo DB - Filter data element in nested array

Question

Query :

db.DEFAULT.find({ "bookStore.books.book.bookId":7501},{"bookStore.books.book.bookId" :1});

Collection :

{
"_id" : ObjectId("5988814feb46972540cebccd"),
"bookStore" : [ 
    {
        "books" : [ 
            {
                "book" : {
                    "bookId" : 7501
                }
            }, 
            {
                "book" : {
                    "bookId" : 7502
                }
            }, 
            {
                "book" : {
                    "bookId" : 7500
                }
            }
        ]
    }
]
}

When I run the query, it displays all the 3 records. Is there anyway only the matching record will be displayed in the results.

mickl · Accepted Answer · 2019-11-12 00:03:54Z

2

You need $map with $filter since your arrays have more than one level of nestings:

db.collection.aggregate([
    {
        $addFields: {
            bookStore: {
                $map: {
                    input: "$bookStore",
                    as: "bs",
                    in: {
                        books: {
                            $filter: {
                                input: "$$bs.books",
                                as: "b",
                                cond: {
                                    $eq: [ "$$b.book.bookId", 7501 ]
                                }
                            }
                        }
                    }
                }
            }
        }
    }
])

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answered Nov 12, 2019 at 0:03

mickl

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