Question 213904 in Json Question posted in
Our archive of expertly curated questions and answers provides insights and solutions to common problems related to this popular data interchange format. From parsing and manipulating JSON data to integrating it with various programming languages and web services, our archive has got you covered. Start exploring today and take your JSON skills to the next level

Json – Expected `Result<Option<Value>, Error>`, found `Result<Option<&…>, …>` on MongoDB

I have this code to connect with MongoDB from rust run when I try to cargo run the code return an error in the if statement and I can’t figure out why. It has been days that I try to debug it.
This is the code:

use std::iter::FilterMap;
use rocket::serde::json::{json, Value};
use futures::{StreamExt};
use mongodb::{bson::doc, options::ClientOptions, Client};
use bson::{Document};
use warp::body::json;

/**
 * MongoDB client
 */
#[tokio::main]
pub async fn database_connection(key: &str, value: &str) -> Result<Option<Value>, mongodb::error::Error> {

    // uri to connect to the database
    let uri = "mongodb://admin:adminpassword@localhost:27017";
    
    // options to connect to the database
    let mut client_options =
        ClientOptions::parse(uri)
        .await?;

    // Create a new client and connect to the server with the given options
    let client = Client::with_options(client_options)?;

    //Connect to the BinGo! database
    let material = client.database("BinGo!");
    
    // Search thrue a collection
    let collection = material.collection::<Document>("bingo_materials");
    
    let filter = doc! {
        key: value
    };
    
    print!("Making the query to the database...n");
    
    println!("Filter: {:#?}", filter);
    print!("-------------------------n");

    let mut cursor = collection.
                find(filter, None)
                .await?;
    
    if let  Some(result) = cursor.next().await {
        println!("{:#?}", result);
        let result_json: &Result<Document, mongodb::error::Error> = &result;
        return Ok(Some(result_json));
    }else{
        return Ok(None);
    }

}

and the error is the following:

error[E0308]: mismatched types
  --> src/databases.rs:57:5
   |
25 |   pub async fn database_connection(key: &str, value: &str) -> Result<Option<Value>, mongodb::error::Error> {
   |                                                               -------------------------------------------- expected `Result<std::option::Option<rocket_dyn_templates::tera::Value>, mongodb::error::Error>` because of return type
...
57 | /     if let  Some(result) = cursor.next().await {
58 | |         println!("{:#?}", result);
59 | |         let result_json: &Result<Document, mongodb::error::Error> = &result;
60 | |         return Ok(Some(result_json));
61 | |     }else{
62 | |         return Ok(None);
63 | |     }
   | |_____^ expected `Result<Option<Value>, Error>`, found `Result<Option<&...>, ...>`
   |
   = note: expected enum `Result<std::option::Option<rocket_dyn_templates::tera::Value>, mongodb::error::Error>`
              found enum `Result<std::option::Option<&Result<bson::Document, mongodb::error::Error>>, _>`

Please be kind, I’m new to rust and I’m still learning.

I’m expecting to return the value of result_json, because database_connection() is called from a route in rocket.rs.

Tags:

2

Answers


  1. 0

    Here are a few tips…

    I suggest that you cargo add serde_json (if you haven’t already done that) and then simply convert your mongodb::bson::Document into serde_json::Value. Here is an example how:

    if let Some(doc) = cursor.try_next().await? {
    let v = serde_json::to_value(&doc).unwrap();
}

    You could also add the popular anyhow crate and make your return type anyhow::Result<Option<serde_json::Value>>. Then you could do something like this:

    if let Some(doc) = cursor.try_next().await? {
    let v = serde_json::to_value(&doc).unwrap();
    return Ok(Some(v));
}
    Login or Signup to reply.
  2. 0

    I think error is here:

    if let  Some(result) = cursor.next().await {
    println!("{:#?}", result);
    let result_json: &Result<Document, mongodb::error::Error> = &result;
    return Ok(Some(result_json));
}else{
    return Ok(None);
}

    in case of error you are returning return Ok(None); but you should be returning mongodb::error::Error> because this is what you added to the function definition:

    pub async fn database_connection(key: &str, value: &str) -> Result<Option<Value>, mongodb::error::Error> {
    Login or Signup to reply.
Please signup or login to give your own answer.

Back To Top
Search