没有为“DbConnection”实现特征“diesel::Connection”

Question

我正在尝试使用柴油将 postgres 数据库添加到火箭应用程序。我的main.rs文件看起来像这样，但给出了错误“该特征diesel::Connection未实现DbConnection”.get_result(connection)

#[macro_use] extern crate diesel;
extern crate dotenv;
#[macro_use] extern crate rocket;
#[macro_use] extern crate rocket_contrib;

use diesel::prelude::*;
use rocket_contrib::database;
use rocket_contrib::json::JsonValue;

mod models;
mod schema;

use self::models::*;
use self::schema::*;

#[database("my_db")]
struct DbConnection(diesel::PgConnection);

#[get("/")]
fn index(connection: DbConnection) -> JsonValue {
    json!(all_bicycles(&connection))
}

fn create_bicycle<'a>(connection: &DbConnection, make: &'a str, model: &'a str, rider_type: &'a str, size: &'a str) -> Bicycle {
    let new_bicycle = NewBicycle {
        make,
        model,
        rider_type,
        size
    };

    diesel::insert_into(bicycles::table)
        .values(new_bicycle)
        // the error is on the following line, on `connection`
        .get_result(connection)
        .expect("Error saving bicycle")
}

fn main() {
    rocket::ignite()
        .attach(DbConnection::fairing())
        .mount("/", routes![index])
        .launch();
}

我的Cargo.toml（相关部分）

[dependencies]
diesel = { version = "1.4.4", features = ["postgres"] }
dotenv = "0.15.0"
rocket = { git = "https://github.com/SergioBenitez/Rocket" }
serde = { version = "1.0", features = ["derive"] }
serde_json = "1.0"

[dependencies.rocket_contrib]
git = "https://github.com/SergioBenitez/Rocket"
default-features = false
features = ["json", "diesel_postgres_pool"]

和我的Rocket.toml：

[global.databases]
my_db = { url = "postgres://postgres:@localhost/bikes" }

展开时错误如下所示：

&DbConnection
the trait bound `DbConnection: diesel::Connection` is not satisfied

the trait `diesel::Connection` is not implemented for `DbConnection`

我已经成功建立了与数据库的连接diesel setup。我还可以添加迁移 - 尽管我认为它们对于这个问题来说是不必要的。

我在这里做错了什么？

编辑

我再次浏览了 Rocket 文档，意识到我错过了use rocket_contrib::databases::diesel;与 冲突的行extern crate diesel;，所以我将数据库逻辑移到了一个新模块中 - database.rs。没有什么真正改变，但新模块看起来像这样：

[dependencies]
diesel = { version = "1.4.4", features = ["postgres"] }
dotenv = "0.15.0"
rocket = { git = "https://github.com/SergioBenitez/Rocket" }
serde = { version = "1.0", features = ["derive"] }
serde_json = "1.0"

[dependencies.rocket_contrib]
git = "https://github.com/SergioBenitez/Rocket"
default-features = false
features = ["json", "diesel_postgres_pool"]

它的使用方式如下：

main.rs

[global.databases]
my_db = { url = "postgres://postgres:@localhost/bikes" }

错误仍然相同。

Answer 1

根据Rocket文档，您需要将连接类型取消引用为某种类型，diesel::connection::Connection因为包装器类型没有实现必要的特征。因此，您需要将代码更改为以下内容：

    diesel::insert_into(bicycles::table)
        .values(new_bicycle)
        // the error is on the following line, on `connection`
        .get_result(&*connection)
        .expect("Error saving bicycle")

&*（请注意将连接传递到函数之前的附加内容get_result。）