如何从mongodb游标获取文档集合? [英] How to get collection of document from mongodb cursor?

问题描述

我有以下代码应该从 mongodb 返回一个文档列表.

I have the following code which should return a list of documents from mongodb.

struct Vehicle{
    id: String,
    name: String
}

pub async fn list_all() -> Vec<Vehicle>{
    let mongodb = connection_bd::connection_mongodb().await;
    let mongodb_collection = mongodb.collection("Vehicle");
    let result = mongodb_collection.find(None, None).await; //result: Result<Cursor<Document>, Error>
    let cursor = match result { //cursor: Cursor<Document>
        Ok(x) => x,
        Err(_) => return vec![]
    };
    //...
}

我无法完成代码，因为我不知道如何将Cursor 转换为Vec，这是我第一次看到光标<文档>，我不知道它是什么.

I can't finish the code because I don't know how to convert Cursor<Document> to Vec<T>, it's my first time seeing Cursor<Document> and I don't know what it is.

更新
错误信息:

error[E0308]: mismatched types
  --> src\vehicle_repo.rs:77:40
   |
77 |   pub async fn list_all() -> Vec<Vehicle>{
   |  ________________________________________^
78 | |     let mongodb = connection_bd::connection_mongodb().await;
79 | |     let mongodb_collection = mongodb.collection("Vehicle");
...  |
84 | |     };
85 | | }
   | |_^ expected struct `Vec`, found `()`
   |
   = note: expected struct `Vec<Vehicle>`
           found unit type `()`

推荐答案

一个 mongodb Cursor 实现了 futures 板条箱.docs 中提到了这一点:

A mongodb Cursor implements Stream from the futures crate. This is mentioned in the docs:

此外，Stream 也可以在 Cursor 上使用.这包括 StreamExt，它提供了与标准库 Iterator trait 类似的功能.例如，如果已知查询的结果数量很少，则将它们收集到一个向量中可能是有意义的:

Additionally, all the other methods that a 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. For instance, if the number of results from a query is known to be small, it might make sense to collect them into a vector:

let results: Vec<Result<Document>> = cursor.collect().await;

我实际上建议使用 TryStreamExt trait 来获取 Result> 代替.然后您可以使用 unwrap_or_else() 返回列表.您还应该使用 collection_with_type() 方法来获取集合，以便您的结果将自动反序列化为正确的类型，而不仅仅是 Document(只需确保它实现了 Debug、Serialize 和 Deserialize).

I would actually recommend using the try_collect() function from the TryStreamExt trait to get a Result<Vec<Document>> instead. Then you can use unwrap_or_else() to return the list. You should also use the collection_with_type() method to get the collection so that your results will be automatically deserialized to the proper type instead of just Document (just make sure it implements Debug, Serialize and Deserialize).

这是一个工作示例

use futures::TryStreamExt;
use mongodb::Client;
use serde::{Deserialize, Serialize};

#[derive(Debug, Serialize, Deserialize)]
struct Vehicle {
    id: String,
    name: String,
}

async fn list_all() -> Vec<Vehicle> {
    let client = Client::with_uri_str("mongodb://example.com").await.unwrap();
    let database = client.database("test");
    let collection = database.collection_with_type::<Vehicle>("vehicles");
    let cursor = match collection.find(None, None).await {
        Ok(cursor) => cursor,
        Err(_) => return vec![],
    };

    cursor.try_collect().await.unwrap_or_else(|_| vec![])
}

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