[英]associated type `Context` not found when implementing actix-web's Handler
I have the following code based on the actix-web Database Integration sample . 我有以下基于actix-web数据库集成示例的代码 。
extern crate actix;
extern crate actix_web;
extern crate serde_json;
#[macro_use]
extern crate serde_derive;
extern crate r2d2;
extern crate r2d2_mysql;
use actix::prelude::*;
use actix_web::{middleware::Logger, server, App, FutureResponse, HttpRequest, HttpResponse};
mod dbservices {
use actix::prelude::*;
use actix_web::dev::Handler;
use model::DataDictionary;
use r2d2::Pool;
use r2d2_mysql::*;
use std::io;
pub struct MysqlConnection {
db_pool: mysql::PooledConn,
}
impl Actor for MysqlConnection {
type Context = SyncContext<Self>;
}
impl MysqlConnection {
pub fn new(db_url: &str) -> MysqlConnection {
unimplemented!();
}
}
pub struct GetDD;
impl Message for GetDD {
type Result = io::Result<Vec<DataDictionary>>;
}
impl Handler<GetDD> for MysqlConnection {
type Result = io::Result<Vec<DataDictionary>>;
fn handle(&mut self, msg: GetDD, _: &mut Self::Context) -> Self::Result {
unimplemented!();
}
}
}
mod model {
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct DataDictionary {
id: i32,
name: String,
}
}
struct State {
db: Addr<MysqlConnection>,
}
fn get_dd(req: HttpRequest<State>) -> FutureResponse<HttpResponse> {
req.clone()
.state()
.db
.send(GetDD)
.from_err()
.and_then(|result| Ok.json(result))
.responder()
}
fn main() {
std::env::set_var("RUST_LOG", "actix_web=debug,info");
const db_url: str = "mysql://connstring";
let addr = SyncArbiter::start(3, move || dbservices::MysqlConnection::new(db_url));
server::new(|| {
App::new()
.middleware(Logger::default())
.middleware(Logger::new("%a %{User-Agent}i"))
.prefix("/api")
.scope("/dd", |dp_scope| {
dp_scope.resource("/", |r| r.h(dbservices::GetDD()))
})
}).bind("127.0.0.1:8088")
.unwrap()
.run();
}
I'm getting the following error when compiling. 编译时出现以下错误。 I'm not sure what I'm doing wrong:
我不确定自己在做什么错:
error[E0220]: associated type `Context` not found for `Self`
--> src/main.rs:43:50
|
43 | fn handle(&mut self, msg: GetDD, _: &mut Self::Context) -> Self::Result {
| ^^^^^^^^^^^^^ associated type `Context` not found
Here are my dependencies from Cargo.toml: 这是我对Cargo.toml的依赖:
[dependencies]
actix-web = "0.6.14"
actix = "0.6.1"
chrono = { version = "0.4.2", features = ["serde"] }
serde = "1.0.60"
serde_derive = "1.0.60"
serde_json = "1.0.17"
log = "0.4.1"
env_logger ="0.5.10"
futures = "0.2.1"
r2d2 = "*"
[dependencies.r2d2_mysql]
git = "https://github.com/outersky/r2d2-mysql"
version="*"
Creating a minimal MCVE almost always makes the problem easier to see: 创建最小的 MCVE几乎总是使问题更容易发现:
extern crate actix;
extern crate actix_web;
use actix::prelude::*;
use actix_web::dev::Handler;
use std::io;
pub struct MysqlConnection;
impl Actor for MysqlConnection {
type Context = SyncContext<Self>;
}
pub struct DummyMessage;
impl Message for DummyMessage {
type Result = io::Result<String>;
}
impl Handler<DummyMessage> for MysqlConnection {
type Result = io::Result<String>;
fn handle(&mut self, _: DummyMessage, _: &mut Self::Context) -> Self::Result {
unimplemented!();
}
}
fn main() {}
error[E0220]: associated type `Context` not found for `Self`
--> src/main.rs:22:53
|
22 | fn handle(&mut self, _: DummyMessage, _: &mut Self::Context) -> Self::Result {
| ^^^^^^^^^^^^^ associated type `Context` not found
actix-web = "0.6.14"
actix = "0.6.1"
This brings in two different versions of actix: 这带来了两个不同版本的actix:
$ cargo tree -d
actix v0.5.8
└── actix-web v0.6.14
└── repro v0.1.0 (file:///private/tmp/repro)
actix v0.6.1
└── repro v0.1.0 (file:///private/tmp/repro)
Pick a single one, actix 0.5.8. 选择一个,actix 0.5.8。
See also: 也可以看看:
You bring in actix_web::dev::Handler
: 您引入
actix_web::dev::Handler
:
pub trait Handler<S>: 'static {
type Result: Responder;
fn handle(&mut self, req: HttpRequest<S>) -> Self::Result;
}
You are implementing actix::Handler
: 您正在实现
actix::Handler
:
pub trait Handler<M>
where
Self: Actor,
M: Message,
{
type Result: MessageResponse<Self, M>;
fn handle(&mut self, msg: M, ctx: &mut Self::Context) -> Self::Result;
}
actix::Handler
has Actor
as its supertrait, which means that it can access the associated type Context
. actix::Handler
以Actor
为特征,这意味着它可以访问关联的Context
类型。 actix_web::dev::Handler
does not have the supertrait, so it doesn't know about Self::Context
. actix_web::dev::Handler
没有超级特性,因此它不了解Self::Context
。
Pick the appropriate trait and implement it correctly. 选择适当的特征并正确实施。
您可以使用SyncContext<Self>
替换Self::Context
This is actually strange since there is only single associated type Context
but for some reason Rust wants you to specify specifically associated type: <Self as Actor>::Context
which should not be required since you have single Context
type 这实际上很奇怪,因为只有单个关联类型
Context
但是出于某种原因Rust希望您指定专门关联的类型: <Self as Actor>::Context
由于您只有单个Context
类型,因此不需要
Are there any other errors that prevent your struct from compiling? 还有其他错误会阻止您的结构进行编译吗?
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