Rust MongoDB API Not Updating Bson Array on Database

Question

So, I am making an API with actix and MongoDB, and I did some testing with the Rust MongoDB API beforehand, in which the basic code goes like this:

// Collections, basically just db names
let users = client.database("userAccounts").collection("users");
let items = client.database("userAccounts").collection("items");

let item: Document = items.find_one(doc!{"type": 0}, None).await?.unwrap();
let mut user: Document = users.find_one(doc!{"username": "Fyre"}, None).await?.unwrap();

let item_id = item.get("_id").unwrap();
let user_id_arr = user.get_array_mut("itemIds")?;

user_id_arr.append(&mut vec![item_id.clone()]);

This works as expected, but when I put very similar code into an Actix service, it doesn't do anything.

pub async fn add_item_to_user_id(path: web::Path<(String, String)>, app_state: web::Data<AppState>) -> impl Responder
{
    let (item_id, user_id) = path.into_inner(); // Same Collections as the Above Code
    if let Ok(id) = mongodb::bson::oid::ObjectId::from_str(&user_id)
    {
        match app_state.users.find_one(doc!("_id": id), None).await
        {
            Ok(opt) => {
                if let Some(mut doc) = opt
                {
                    if let Ok(ids) = doc.get_array_mut("itemIds")
                    {
                        ids.append(&mut vec![bson::Bson::String(item_id)]);
                        HttpResponse::Ok().body("Item Added!")
                    }
                    else
                    {
                        HttpResponse::InternalServerError().body("Failed to add item?")
                    }
                }
                else
                {
                    HttpResponse::InternalServerError().body("Error Adding Item!")
                }
            },
            Err(err) => HttpResponse::BadRequest().body(format!["Invalid ID!: {}", err])
        }
    }
    else
    {
        HttpResponse::BadRequest().body("Invalid ID!")
    }
}

In the database, the users are reperesented as:

{
    _id: ObjectId("64bef1dc19f7e4334f241ae8"),
    username: 'Fyre',
    email: '[REDACTED]',
    itemIds: []
}

But after the modifications, it should look like:

{
    _id: ObjectId("64bef1dc19f7e4334f241ae8"),
    username: 'Fyre',
    email: '[REDACTED]',
    itemIds: [ '64bef1dc19f7e4334f241ae9' /* Mongo ID of random item in DB */ ]
}

I have also tried to get the array, change in the rust code, and replace using the update() command, and that did work, but I'm wondering why the other method didn't.¯\(ツ)/¯