Rust操作MongoDB更新模型时遭遇E0532编译错误求助

问题场景 #

想要在Rust中更新MongoDB的整个User模型，避免逐个字段编写$set语句，编写对应代码后出现编译错误。

原代码 #

use mongodb::{bson, bson::doc, Client, Collection};

let collection: Collection<User> =
               client.database(DB_NAME).collection(users::REPOSITORY_NAME);
let filter = doc! {"email": new_user_copy.email};
let new_user_bson = match bson::to_bson(&new_user_copy) {
    bson::Document(doc) => doc,
    _ => unreachable!(),
};
let update = doc! {"$set": new_user_bson};
let result = collection.update_one(filter, update, None).await;

编译错误 #

error[E0532]: expected tuple struct or tuple variant, found struct Document
--> src/controllers/users.rs:82:17
|
82 | Document(doc) => doc,
| ^^^^^^^^^^^^^
|
::: /Users/adrien/.cargo/registry/src/github.com-1ecc6299db9ec823/bson-2.6.1/src/document.rs:63:1
|
63 | pub struct Document {
| ------------------- Document defined here
|
help: use struct pattern syntax instead
|
82 | Document { inner } => doc,
| ~~~~~~~~~~~~~~~~~~
help: consider importing one of these items instead
|
1 | use crate::controllers::users::bson::Bson::Document;
|
1 | use crate::controllers::users::bson::RawBson::Document;
|
1 | use crate::controllers::users::bson::RawBsonRef::Document;
|
1 | use mongodb::options::UpdateModifications::Document;

错误原因 #

bson::to_bson返回的是Bson枚举类型，其中的Document是该枚举的一个变体，而非直接的bson::Document结构体。原代码中直接写bson::Document(doc)是在匹配结构体，而非枚举变体，导致编译错误。

解决方法 #

方法1：明确匹配Bson枚举的Document变体 #

修改match语句，指定枚举变体bson::Bson::Document：

use mongodb::{bson, bson::doc, Client, Collection};

let collection: Collection<User> =
               client.database(DB_NAME).collection(users::REPOSITORY_NAME);
let filter = doc! {"email": new_user_copy.email};
let new_user_bson = match bson::to_bson(&new_user_copy) {
    bson::Bson::Document(doc) => doc, // 明确指定枚举变体
    _ => unreachable!(),
};
let update = doc! {"$set": new_user_bson};
let result = collection.update_one(filter, update, None).await;

方法2：导入Bson枚举的Document变体简化代码 #

在开头导入bson::Bson::Document，匹配时可直接写Document(doc)：

use mongodb::{bson, bson::Bson::Document, bson::doc, Client, Collection};

let collection: Collection<User> =
               client.database(DB_NAME).collection(users::REPOSITORY_NAME);
let filter = doc! {"email": new_user_copy.email};
let new_user_bson = match bson::to_bson(&new_user_copy) {
    Document(doc) => doc,
    _ => unreachable!(),
};
let update = doc! {"$set": new_user_bson};
let result = collection.update_one(filter, update, None).await;

方法3：使用bson::to_document直接转换（更简洁） #

无需通过to_bson再匹配，直接用to_document将User实例转为Document：

use mongodb::{bson, bson::doc, Client, Collection};

let collection: Collection<User> =
               client.database(DB_NAME).collection(users::REPOSITORY_NAME);
let filter = doc! {"email": new_user_copy.email};
let new_user_doc = bson::to_document(&new_user_copy)?; // 直接转为Document，用?处理错误
let update = doc! {"$set": new_user_doc};
let result = collection.update_one(filter, update, None).await;

注：实际代码中建议用?替代unwrap()处理转换错误，提升程序健壮性。

内容的提问来源于stack exchange，提问作者Adrien Chapelet