Rust CRUD新增接口出现`Bson: Borrow<News>` trait未满足错误

问题 #

使用Axum与MongoDB实现新闻新增接口post_news时，出现编译错误E0277：提示Bson未实现Borrow<News> trait，错误触发于coll.insert_one(serialized_news, None)代码行。已尝试为News结构体添加Clone和Debug trait，但问题未解决。

错误信息 #

error[E0277]: the trait bound `Bson: Borrow<News>` is not satisfied                                                                                                                               
    --> src\handlers.rs:46:36
     |
46   |     let inserted = coll.insert_one(serialized_news, None).await.unwrap();
     |                         ---------- ^^^^^^^^^^^^^^^ the trait `Borrow<News>` is not implemented for `Bson`
     |                         |
     |                         required by a bound introduced by this call
     |
note: required by a bound in `mongodb::Collection::<T>::insert_one`
    --> C:\Users\User\.cargo\registry\src\github.com-1ecc6299db9ec823\mongodb-2.3.1\src\coll\mod.rs:1279:19
     |
1279 |         doc: impl Borrow<T>,
     |                   ^^^^^^^^^ required by this bound in `mongodb::Collection::<T>::insert_one`

For more information about this error, try `rustc --explain E0277`.  
error: could not compile `backend` due to previous error

相关代码 #

use crate::structs::News;
use axum::{extract::Path, extract::State, http::StatusCode, response::IntoResponse, Json};
use bson::oid::ObjectId;
use futures::stream::StreamExt;
use mongodb::{bson::doc, options::FindOptions, Client, Collection};

pub async fn get_all(State(client): State<Client>) -> impl IntoResponse {
    let coll: Collection<News> = client.database("axum").collection::<News>("news");

    let mut options = FindOptions::default();
    options.limit = Some(1);
    options.sort = Some(doc! {
        "title": 1
    });

    let mut cursor = coll
        .find(None, options)
        .await
        .expect("could not load news data.");

    let mut rows: Vec<News> = Vec::new();

    while let Some(doc) = cursor.next().await {
        rows.push(doc.expect("could not load news info."));
    }

    (StatusCode::OK, Json(rows))
}

pub async fn get_one(Path(id): Path<u64>) {}

pub async fn post_news(
    State(client): State<Client>,
    Json(payload): Json<News>,
) -> impl IntoResponse {
    let coll: Collection<News> = client.database("axum").collection::<News>("news");

    let news = News {
        id: ObjectId::new(),
        title: payload.title.to_string(),
        short_description: payload.short_description.to_string(),
    };

    let serialized_news = bson::to_bson(&news).unwrap();

    let inserted = coll.insert_one(serialized_news, None).await.unwrap();

    (StatusCode::CREATED, Json(news))
}

pub async fn handler_404() -> impl IntoResponse {
    (StatusCode::NOT_FOUND, "nothing to see here")
}

mod structs {
    use bson::{self, oid::ObjectId};
    use serde::{Deserialize, Serialize};

    #[derive(Debug, Serialize, Deserialize)]
    #[serde(rename_all = "snake_case")]
    pub struct News {
        #[serde(rename = "_id")]
        pub id: ObjectId,
        pub title: String,
        pub short_description: String,
    }
}

错误触发代码行 #

let inserted = coll.insert_one(serialized_news, None).await.unwrap();

解决方案 #

错误核心原因：Collection<News>的insert_one方法要求参数实现Borrow<News>约束，但手动将News序列化为Bson后，Bson类型并不满足该约束。MongoDB Rust驱动会自动处理结构体的序列化/反序列化，无需手动转换为Bson。

修改post_news函数，删除手动序列化步骤，直接传入&news即可：

pub async fn post_news(
    State(client): State<Client>,
    Json(payload): Json<News>,
) -> impl IntoResponse {
    let coll: Collection<News> = client.database("axum").collection::<News>("news");

    let news = News {
        id: ObjectId::new(),
        title: payload.title.to_string(),
        short_description: payload.short_description.to_string(),
    };

    // 直接传入&news，驱动自动完成序列化
    let inserted = coll.insert_one(&news, None).await.unwrap();

    (StatusCode::CREATED, Json(news))
}

注：确保News结构体已正确实现Serialize和Deserialize trait（你的代码中已满足该条件），这是驱动自动序列化的前提。

内容的提问来源于stack exchange，提问作者Azashiro Merume