cannot infer type for type parameter `T` declared on the associated function `collection`-CodePudding

I am trying to connect to Mongo DB from rust. I am following the tutorial here. But I am getting the below error. I did run rustup update and I have the latest 1.59 version.

error[E0282]: type annotations needed for `mongodb::Collection<T>`
  --> src/main.rs:27:46
   |
27 | let movies = client.database("sample_mflix").collection("movies");
   |     ------                                   ^^^^^^^^^^ cannot infer type for type parameter `T` declared on the associated function `collection`
   |     |
   |     consider giving `movies` the explicit type `mongodb::Collection<T>`, where the type parameter `T` is specified

For more information about this error, try `rustc --explain E0282`.
error: could not compile `try-mongo` due to previous error

Below is the code I have written.

use mongodb::{Client, options::{ClientOptions, ResolverConfig}};
use std::env;
use std::error::Error;
use tokio;

#[tokio::main]
async fn main() -> Result<(), Box<dyn Error>> {
   // Load the MongoDB connection string from an environment variable:
   let client_uri =
      env::var("MONGODB_URI").expect("You must set the MONGODB_URI environment var!");

   // A Client is needed to connect to MongoDB:
   // An extra line of code to work around a DNS issue on Windows:
   let options =
      ClientOptions::parse_with_resolver_config(&client_uri, ResolverConfig::cloudflare())
         .await?;
   let client = Client::with_options(options)?;

   // Print the databases in our MongoDB cluster:
   println!("Databases:");
   for name in client.list_database_names(None, None).await? {
      println!("- {}", name);
   }


   // Get the 'movies' collection from the 'sample_mflix' database:
let movies = client.database("sample_mflix").collection("movies");

   Ok(())
}

In Cargo.toml I have the below dependecies added -

[package]
name = "try-mongo"
version = "0.1.0"
edition = "2021"

[dependencies]
mongodb = "2.1"
bson = { version = "2", features = ["chrono-0_4"] } # Needed for using chrono datetime in doc
tokio = "1"
chrono = "0.4" # Used for setting DateTimes
serde = "1" # Used in the Map Data into Structs section`

CodePudding user response：

Did you try specifying the type let movies: mongodb::Collection<_>?

CodePudding user response：

So the solution to this is to specify the mongodb::bson::Document type to the collection function call. Like below -

let movies = client.database("sample_mflix").collection::<Document>("movies");