I’m not able to load just one element of an array at a lower level on mongodb

Question

Person I’m trying to pull just one helper, I’m doing the following,

db.colecao.find( { functio.nome : joão }, { 'functionary.helper. $' 1 } );

but always comes everyone, I’ve tried several ways, Bs there in helper could have much more and dynamic

{
    empresa : 'nome da empresa',
    funcionario : [
        {
            nome : 'joão',
            ajudante : [
                {
                    nome : manoel,
                    idade : 24
                },
                {
                    nome : joel,
                    idade : 20
                }
            ]
        }
    ]
}

Answer 1

From what I understand you want to return only the helpers(s) of some employee.

find will always return a document from Collection, returning the document and the structure to support your projection. If you run this query:

db.teste.find(
     {"funcionario.nome": "joão", "funcionario.ajudante.nome": 'manoel'}, 
     {"funcionario.ajudante.nome": 1}
)

The return will include the array with all elements, but showing only the name of each helper. This is because in the query you are asking for a document that has an employee with name "john", that has a helper with name "Manoel".

If you want to return only the helper in question, you need to use an aggregation:

db.teste.aggregate(
    {$match: {"funcionario.nome" : "joão"}}, 
    {$project: {"funcionario.nome" : 1, "funcionario.ajudante" : 1}}, 
    {$unwind: "$funcionario"}, 
    {$unwind: "$funcionario.ajudante"},
    {$match: {"funcionario.ajudante.nome" : "manoel"}}
)

If you are going to get helpers from someone who knows how often it is worth putting them in a separate Collection, and save only the names or _id in an array within the employee.

Most important: It makes no sense to keep the company, its employees and helpers in a document only if you don’t want to recover it at once from the bank.

Gives a research on modeling in Mongo, the most important thing is to think how you will access/modify the data.