[英]How to return a State value from a Rocket endpoint?
我将来自外部服务的数据存储在本地缓存中,我想创建一个端点来返回当前缓存中的数据。
#![feature(proc_macro_hygiene, decl_macro)]
#[macro_use]
extern crate rocket;
use rocket::{Route, State};
use rocket_contrib::json::Json;
use serde::{Deserialize, Serialize};
#[derive(Serialize, Deserialize)]
pub struct Post {
pub title: String,
pub body: String,
}
impl Post {
pub fn new(title: String, body: String) -> Post {
Post { title, body }
}
}
pub struct Cache {
pub posts: Vec<Post>,
}
impl Cache {
pub fn new() -> Cache {
let mut posts = vec![
Post::new(String::from("Article1"), String::from("Blah")),
Post::new(String::from("Article2"), String::from("Blah")),
Post::new(String::from("Article3"), String::from("Blah")),
Post::new(String::from("Article4"), String::from("Blah")),
Post::new(String::from("Article5"), String::from("Blah")),
];
Cache { posts }
}
}
#[derive(Responder)]
pub enum IndexResponder {
#[response(status = 200)]
Found(Json<Vec<Post>>),
#[response(status = 404)]
NotFound(String),
}
#[get("/")]
pub fn index(cache: State<Cache>) -> IndexResponder {
return IndexResponder::Found(Json(cache.posts));
}
fn main() {
rocket::ignite()
.mount("/", routes![index])
.manage(Cache::new())
.launch();
}
编译器抱怨:
error[E0507]: cannot move out of dereference of `rocket::State<'_, Cache>`
--> src/main.rs:50:39
|
50 | return IndexResponder::Found(Json(cache.posts));
| ^^^^^^^^^^^ move occurs because value has type `std::vec::Vec<Post>`, which does not implement the `Copy` trait
我的Cargo.toml文件:
[package]
name = "debug-project"
version = "0.1.0"
authors = ["Varkal <mail@example.com>"]
edition = "2018"
[dependencies]
rocket = "0.4.0"
rocket_contrib = "0.4.0"
serde = { version = "1.0.90", features = ["derive"] }
serde_json = "1.0.39"
您的端点不拥有该状态,因此无法返回拥有的Vec<Post>
。 从概念上讲,这是有道理的,因为如果您确实拥有它,那么下次调用端点时会出现什么值?
您可以做的最简单的事情是克隆数据:
#[get("/")]
pub fn index(cache: State<Cache>) -> IndexResponder {
IndexResponder::Found(Json(cache.posts.clone()))
}
这将要求您实现Clone
for Post
,或者可能更改您的状态以保存类似Arc
。
性能略高的解决方案是返回引用状态的切片。 这不需要克隆,但需要使用State::inner
方法:
#[derive(Responder)]
pub enum IndexResponder<'a> {
#[response(status = 200)]
Found(Json<&'a [Post]>),
#[response(status = 404)]
NotFound(String),
}
#[get("/")]
pub fn index<'a>(cache: State<'a, Cache>) -> IndexResponder<'a> {
IndexResponder::Found(Json(&cache.inner().posts))
}
也可以看看:
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