Help - some direction? Futures, mongodb, stream::collect()

help
1

I'm trying to figure out how to use the mongodb driver 1.1.1

I have not included code, because I am hoping just for a nudge in the right direction.

I've got a function with a client with a connection to the Database and collection (that seems to be fine), but when I try to use the supposed returned cursor from a find method, I am getting a future, not a cursor. Now I accept that that is how futures work, but I can't find any information in how to get the actual cursor. I need the future to complete and I can't seem to find anything that says how to do that.

I watched the rustfest barcelona video on async that suggests using task::block_on, but either that isn't right or more likely I am using it completely wrong.

Can kind soul please point me in the right direction? I'm spinning my wheels here feeling like I'm going to go insane.

2

Could you post your code where you're using block_on? That does sound like the right approach for your use-case, but it's hard to tell what's going wrong.

3

If you are not already using async/await for some other reason, I recommend using the mongodb::sync module, which does not require messing with block_on and the likes.

1 Like
4

Sorry, due to work conditions I have been afk for a couple days.
But I got it working! Turns out I forgot to await inside the task. I also decided not to use collect(). Here is the code that works(as in compiles and does reach out to the mongo db), it's really bad as I am just starting out, so feel free to point me to any improvements.

pub async fn get_data(datb: &str, col:&str, docu: Document)->Vec<String>{
let client = match Client::with_uri_str("mongodb://localhost:27017").await {
    Ok(c)=>c,
    Err(e)=>panic!("Could not reach client"),
};
let coll = client.database(datb).collection(col);
let mut cursor = match coll.find(docu,None).await{
    Ok(cursor)=>cursor,
    Err(e)=>panic!("Problem with the database"),
};
let mut docs= Vec::new();
while let Some(result) = cursor.next().await {
    match result {
        Ok(document) => {
            if let Some(title) = document.get("author").and_then(Bson::as_str) {
                docs.push(String::from(title));
            }  else {
                println!("no titles found");
            }
        }
        Err(e) => panic!("error getting data:{}",e ),
    }
}
docs
}

fn main() {
let data = task::block_on(async{get_data("library","books"|,doc!{"author":"test"}).await});
    println!("{:?}",data);
}
5

Whenever you have

match x {
    Ok(val) => do_something_with(val),
    Err(_) => panic!("oh no"),
}

you can instead use the shorter and more idiomatic

do_something_with(x.expect("oh no"))

See Result::expect and the book chapter on error handling. (There is also Option::expect, which works similarly.)

6

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