How to use Mongodb::cursor in Rust? - mongodb

Question

It's a very simple project to learn how to use mongodb with Rust. I'm using the official mongodb driver here: https://github.com/mongodb/mongo-rust-driver. The problem is that if I'm using aggregate, I cannot read the result
// main.rs
use mongodb::bson::{doc, Bson};
use mongodb::{options::AggregateOptions, options::ClientOptions, Client};
use std::error::Error;
use tokio;
#[tokio::main]
async fn main() -> Result<(), Box<dyn Error>> {
// Load the MongoDB connection string:
let client_uri = "mongodb://127.0.0.1:27017";
// A Client is needed to connect to MongoDB:
let mut options = ClientOptions::parse(&client_uri).await?;
options.app_name = Some("testing".to_string());
let client = Client::with_options(options)?;
// get the collection here
let items = client.database("my_database").collection("inventory");
// aggregate options and pipeline
let pipeline = vec![doc! {"$match": {"name": "FOO"}}];
let options = AggregateOptions::builder().allow_disk_use(true).build();
// I'm using tokio for async-await library
let data = items
.aggregate(pipeline, options)
.await
.map_err(|e| println!("{}", e));
// data is a Result<mongodb::Cursor> type
match data {
Ok(cursor) => {
// I want to iterate the returned documents here
// this doesn't compiles
while let Some(doc) = cursor.next().await {
println!("{}", doc?)
}
},
Err(e) => println!("{:?}", e),
}
The code above returns an error. It complains that the cursor has no next() function within.
while let Some(doc) = cursor.next().await {
| ^^^^ method not found in `mongodb::Cursor`
I read the manual book for mongodb::Cursor here: https://docs.rs/mongodb/1.2.1/mongodb/struct.Cursor.html
and aggregate function here https://docs.rs/mongodb/1.2.1/mongodb/struct.Collection.html#method.aggregate
As you can see the aggregate method should return Result<Cursor>. As the manual stated:
A cursor can be used like any other Stream. The simplest way is just
to iterate over the documents it yields:
while let Some(doc) = cursor.next().await {
println!("{}", doc?)
}
So why is it doesn't work ?
My dependencies in Cargo.toml:
[dependencies]
tokio = { version = "0.2", features = ["macros", "rt-threaded"] }
serde = { version = "1.0", features = ["derive"] }
mongodb = "1.2.0"
If I print the cursor println!("{:?}", cursor);. It contains data in it. How to get the data out from this cursor ?

Answer 1

I found it! Just add use tokio::stream::StreamExt; on top of the file and the rest is good to go.
...all the other methods that an Stream has are available on Cursor as
well. This includes all of the functionality provided by StreamExt,
which provides similar functionality to the standard library Iterator
trait.
// main.rs
use mongodb::bson::{doc, Bson};
use mongodb::{options::AggregateOptions, options::ClientOptions, Client};
use std::error::Error;
use tokio;
// don't forget this!
use tokio::stream::StreamExt;

Answer 2

Fixed it by adding use futures::stream::StreamExt;