MongoDB returns only the specified query - mongodb

Question

db.customerOrder.insert({
firstName: "Andrew",
lastName: "Lee",
DOB: ISODate("1974-10-28T00:00:00Z"),
phone: "[phone]",
email: "mark#gmail.com",
address: {
street: "Cornish Street, Victoria",
houseNumber: "68",
postalCode: "3024",
country: "Australia",
},
language: ["English", "Mandarin"],
balance: 0,
orders: [
{
orderNumber: "ord003",
orderDate: ISODate("2020-01-10T00:00:00Z"),
staffNumber: "stf789"
}
]
});
Given the document above, and other documents which contain other orders and order number, how do i specify an aggregation so that it will only list all orderNumbers that's handled by a staffNumber x?
Example, orderNumber ord004 and ord005 is handled by staffNumber stf890
I tried doing
db.customerOrder.aggregate([ {"$match":{"orders.staffNumber":"stf890"}}, {"$project":{"orders.orderNumber":1, "_id":0}} ])
but the result was
{
"orders" : [
{
"orderNumber" : "ord003"
},
{
"orderNumber" : "ord003"
},
{
"orderNumber" : "ord005"
}
]
}
{
"orders" : [
{
"orderNumber" : "ord001"
},
{
"orderNumber" : "ord005"
}
]
}
{
"orders" : [
{
"orderNumber" : "ord003"
},
{
"orderNumber" : "ord004"
}
]
}
I expect the result to output only ord004 and ord005
How do i achieve this?
Thank you for your help

Answer 1

Try this! your query is almost correct but you're missing the case of matching orderNumber.
db.customerOrder.aggregate([
{
"$match":{
"orders.staffNumber":"stf890"
}
},
{
$unwind:{
"path":"$orders"
}
},
{
"$match":{
"orders.orderNumber":{$in:["ord004","ord005"]}
}
},
{
"$project":{
"orders.orderNumber":1,
"_id":0
}
}
])

Answer 2

If you don't care about the structure you can just $unwind and then match. otherwise you need to use something like $filter
Option 1:
db.customerOrder.aggregate([
{
"$match": {
"orders.staffNumber": "stf890"
}
},
{
"$unwind": "$orders"
},
{
"$match": {
"orders.staffNumber": "stf890"
}
},
{
"$project": {"orders.orderNumber": 1, "_id": 0}
}])
Option 2:
db.customerOrder.aggregate([
{
"$match": {
"orders.staffNumber": "stf890"
}
},
{
$project: {
orders: {
$filter: {
input: "$orders",
as: "order",
cond: {
$eq: ["$$order.staffNumber", "stf890"]
}
}
}
}
},
{
"$project": {
"orders.orderNumber": 1,
"_id": 0
}
}
])