mongoDb embedded query to find list of data

Question

I have the following embedded data And I am trying to get all the transactions which have a same week number for a particular saved account based on the accountId . I tried the following query but it returns an empty array.

savingsAccount.find({accountId: "123456789012345678", transactions: {weekNumber: 32}})

Any Ideas? Thanks so much in advance.

    "savingsAccount":
    {
        "_id": "598cb8686739d49a6f59dbb4",
        "accountId": "123456789012345678",
        "__v": 2,
        "transactions": [
            {
                "_id": "598cb8a86739d49a6f59dbb5",
                "amount": 1234,
                "weekNumber": 32,
                "date": "2017-08-10T19:48:56.347Z"
            },
            {
                "_id": "598cbb70a4a8f89c18309d87",
                "amount": 1234,
                "weekNumber": 32,
                "date": "2017-08-10T20:00:48.241Z"
            }
        ]
    }

Answer 1

This ...

savingsAccount.find({
    accountId: "123456789012345678", 
    'transactions.weekNumber': 32
})

... will return all documents for which accountId is "123456789012345678" and the weekNumber attribute of at least one subdocument in the transactions array is 32.

Your original query returned no matches because the second predicate ( transactions: {weekNumber: 32} ) was attempting to match elements of the transactions array with the value: {weekNumber: 32} and, since that only represents part of a transactions document, no match was found.

Edit 1 : if you want to go further than this to only return the subdocuments in the transactions array which have weekNumber=32 then you have to project and filter (available in versions >= 3.2). Here's an example:

db.savingsAccount.aggregate([
    {$match: { accountId: "123456789012345678" }},
    {$project: {
        accountId: 1,
        __v: 1,
        transactions: {$filter: {
            input: '$transactions',
            as: 't',
            cond: {$eq: ['$$t.weekNumber', 32]}
        }}
    }}
])

This will return all documents for which accountId is "123456789012345678" and the weekNumber attribute of at least one subdocument in the transactions array is 32 and for each matched document it will filter the transactions array such that only those subdocuments having weekNumber=32 are returned.