How to change the type of field in an array of sub-documents - mongodb

Question

I have a collection of documents, each of which possesses an array of subdocuments (ranging from 1-10,000 objects). In a small portion of these documents, a field in the arrayed sub-documents has been set to a string instead of an integer and I need to convert these values to an Integer
Here is a structural sample. Note that the DB Admin built the database and collection names with a '.' notation which has complicated some of my work thus far:
Collection Name: "employee.roster"
{
"_id" : ObjectId("5f11d4c28663f32e940696e0"),
"PdfId" : NumberInt(100),
"Staff" : [
{
"StaffId" : NumberInt(1),
"StaffName" : "John Doe"
},
{
"StaffId" : NumberInt(2),
"StaffName" : "John Smith"
},
{
"StaffId" : "3",
"StaffName" : "John Jones"
}
]
}
{
"_id" : ObjectId("5f11d4c28663f32e940696e1"),
"PdfId" : NumberInt(110),
"Staff" : [
{
"StaffId" : "4",
"StaffName" : "Bob Loblaw"
},
{
"StaffId" : NumberInt(5),
"StaffName" : "Edward Nigma"
},
{
"StaffId" : "6",
"StaffName" : "Hugh Mongus"
}
]
}
I have tried a variety of methods without success. Based on other posts, I thought something like this should work but I've generated nothing but errors:
db.getCollection("staff.roster").update(
{},
[{ $set: { "Staff.$[elem].StaffId": { $toInt: "$Staff.$[elem].StaffId" } } }],
{ "arrayFilters": [{ "elem.StaffId": { $type: 2 } } ], "multi": true }
)
ERROR MESSAGE:
WriteResult({
"nMatched" : 0,
"nUpserted" : 0,
"nModified" : 0,
"writeError" : {
"code" : 9,
"errmsg" : "arrayFilters may not be specified for pipeline-syle updates"
}
})
I've also tried this but I believe my notation is wrong because of the sub-documents:
db.getCollection("staff.roster").find( { "Staff.StaffId" : { $type : 2 } } ).forEach( function (x) {
x."Staff.StaffId" = new NumberInt(x."Staff.StaffId");
db.getCollection("staff.roster").save(x);
});
My output should look like this:
{
"_id" : ObjectId("5f11d4c28663f32e940696e0"),
"PdfId" : NumberInt(100),
"Staff" : [
{
"StaffId" : NumberInt(1),
"StaffName" : "John Doe"
},
{
"StaffId" : NumberInt(2),
"StaffName" : "John Smith"
},
{
"StaffId" : NumberInt(3),
"StaffName" : "John Jones"
}
]
}
{
"_id" : ObjectId("5f11d4c28663f32e940696e1"),
"PdfId" : NumberInt(110),
"Staff" : [
{
"StaffId" : NumberInt(4),
"StaffName" : "Bob Loblaw"
},
{
"StaffId" : NumberInt(5),
"StaffName" : "Edward Nigma"
},
{
"StaffId" : NumberInt(6),
"StaffName" : "Hugh Mongus"
}
]
}

Answer 1

You can use update with aggregation pipeline starting from MongoDB 4.2,
$map to iterate loop of Staff array, change the type of StaffId and merge objects with other fields using $mergeObjects
db.getCollection("staff.roster").update({},
[{
$set: {
Staff: {
$map: {
input: "$Staff",
in: {
$mergeObjects: [
"$$this",
{ StaffId: { $toInt: "$$this.StaffId" } }
]
}
}
}
}
}]
)
Playground