Monodb query nested object by two fields

I need to get a document from "documents" by clientId and documentId. How can I retrieve the data?
Schema:

{
    _id: ObjectId('64cd1e1877dd3b45ce2715d4'),
    name: 'string',
    clientId: '79fc89fe-32de-11ee-be56-0242ac120002',
    dateBirth: ISODate('2023-08-04T10:49:30.594Z'),
    addressReg: 'string',
    addressFact: 'string',
    passportSeries: 'string',
    passportNumber: 'string',
    mobilePhone: 'string',
    anotherMobilePhone: 'string',
    email: 'string',
    oneMoreEmail: 'string',
    cardName: 'string',
    currencyName: 'string',
    paymentSystem: 'string',
    tariff: 'string',
    signingDate: ISODate('2023-08-04T10:49:30.594Z'),
    documents: [
        {
            clientId: '79fc89fe-32de-11ee-be56-0242ac120002',
            documentId: '64cd160a68f6d71fc5f68098',
            title: 'T_rules.md',
            signed: true
        }
    ],
    _class: 'com.example.mvpmongo.model.ClientData'
}

When I try this query I get null, though clientId and documentId are correct.

   @Query("{ $and: [{'documents' : { $elemMatch: {'documentId': ?1}}},{'clientId': ?0}]}")
    SignedDocument findDocument(String clientId, String documentId);

I'm new to mongo, could you please explain to me what I am doing wrong.

There are multiple solutions to your problem. I created a GitHub repo showing the different options:

1. Creating a custom query

In your case the query would look as follows:

@Query(value = "{ $and: [{'documents.clientId' :  ?0},{'documents.documentId' :  ?1}]}", fields = "{ 'documents' : 1}")
ClientData findDocument(String clientId, String documentId);

Note that this query returns ClientData (including the entire list of SignedDocument), so you still need to filter the result afterwards.

*the fields parameter is not mandatory, but in case there are many attributes you can use it to indicate which attributes you want to retrieve. The others are null.

2. Creating a custom method

ClientData findByDocuments_ClientIdAndDocuments_DocumentId(String clientId, String documentId);

In this case Spring derives the query from the method name directly.
Note that you still need to do the filtering, since you retrieve the ClientData object.

3. Use unwinding

This one is a bit more complex. Basically, you need to create a separate class SignedDocumentUnwinded and convert the result of your query to this class.

UnwindOperation unwind = Aggregation.unwind("documents");
MatchOperation match = Aggregation.match(Criteria.where("documents.clientId").is(requestedClientId).and("documents.documentId").is(requestedDocumentId));
Aggregation aggregation = Aggregation.newAggregation(unwind, match);
AggregationResults<SignedDocumentUnwind> results = mongoTemplate.aggregate(aggregation, "client_data",
                SignedDocumentUnwind.class);
return results.getMappedResults().stream().map(SignedDocumentUnwind::getDocuments).toList();

The advantage is that there's no need to filter for the requested SignedDocument.